Add support to create device_links between dmaengine suppliers and the
dma consumers. This shifts the device dep-chain teardown/bringup logic
to the driver core.
Moving this to the core allows the dmaengine drivers to simplify the
.remove() hooks and also to ensure that no dmaengine driver is ever
removed before the consumer is removed.
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
---
drivers/dma/dmaengine.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
struct fwnode_handle *fwnode = dev_fwnode(dev);
struct dma_device *d, *_d;
struct dma_chan *chan = NULL;
+ struct device_link *dl;
if (is_of_node(fwnode))
chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
@@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
/* No functional issue if it fails, users are supposed to test before use */
#endif
+ dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
+ if (!dl) {
+ dev_err(dev, "failed to create device link to %s\n",
+ dev_name(chan->device->dev));
+ return ERR_PTR(-EINVAL);
+ }
+
chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
if (!chan->name)
return chan;
--
2.47.2On Wed, Sep 03, 2025 at 03:06:17PM +0200, Marco Felsch wrote:
> Add support to create device_links between dmaengine suppliers and the
> dma consumers. This shifts the device dep-chain teardown/bringup logic
> to the driver core.
>
> Moving this to the core allows the dmaengine drivers to simplify the
> .remove() hooks and also to ensure that no dmaengine driver is ever
> removed before the consumer is removed.
>
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
Thank you work for devlink between dmaengine and devices. I have similar
idea.
This patch should be first patch.
The below what planned commit message in my local tree.
Implementing runtime PM for DMA channels is challenging. If a channel
resumes at allocation and suspends at free, the DMA engine often remains on
because most drivers request a channel at probe.
Tracking the number of pending DMA descriptors is also problematic, as some
consumers append new descriptors in atomic contexts, such as IRQ handlers,
where runtime resume cannot be called.
Using a device link simplifies this issue. If a consumer requires data
transfer, it must be in a runtime-resumed state, ensuring that the DMA
channel is also active by device link. This allows safe operations, like
appending new descriptors. Conversely, when the consumer no longer requires
data transfer, both it and the supplier (DMA channel) can enter a suspended
state if no other consumer is using it.
Introduce the `create_link` flag to enable this feature.
also suggest add create_link flag to enable this feature in case some
side impact to other dma-engine. After some time test, we can enable it
default.
> drivers/dma/dmaengine.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> struct fwnode_handle *fwnode = dev_fwnode(dev);
> struct dma_device *d, *_d;
> struct dma_chan *chan = NULL;
> + struct device_link *dl;
>
> if (is_of_node(fwnode))
> chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> /* No functional issue if it fails, users are supposed to test before use */
> #endif
>
> + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
chan->device->dev is dmaengine devices. But some dmaengine's each channel
have device, consumer should link to chan's device, not dmaengine device
because some dmaengine support per channel clock\power management.
chan's device's parent devices is dmaengine devices. it should also work
for sdma case
if (chan->device->create_devlink) {
u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
if (pm_runtime_active(dev))
flags |= DL_FLAG_RPM_ACTIVE;
When create device link (apply channel), consume may active.
dl = device_link_add(chan->slave, &chan->dev->device, flags);
}
Need update kernel doc
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index bb146c5ac3e4c..ffb3a8f0070ba 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -323,7 +323,8 @@ struct dma_router {
* @cookie: last cookie value returned to client
* @completed_cookie: last completed cookie for this channel
* @chan_id: channel ID for sysfs
- * @dev: class device for sysfs
+ * @dev: class device for sysfs, also use for pre channel runtime pm and
+ * use custom/different dma-mapping
Frank
> + if (!dl) {
> + dev_err(dev, "failed to create device link to %s\n",
> + dev_name(chan->device->dev));
> + return ERR_PTR(-EINVAL);
> + }
> chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
> if (!chan->name)
> return chan;
>
> --
> 2.47.2
>
Hi Frank,
On 25-09-03, Frank Li wrote:
> On Wed, Sep 03, 2025 at 03:06:17PM +0200, Marco Felsch wrote:
> > Add support to create device_links between dmaengine suppliers and the
> > dma consumers. This shifts the device dep-chain teardown/bringup logic
> > to the driver core.
> >
> > Moving this to the core allows the dmaengine drivers to simplify the
> > .remove() hooks and also to ensure that no dmaengine driver is ever
> > removed before the consumer is removed.
> >
> > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > ---
>
> Thank you work for devlink between dmaengine and devices. I have similar
> idea.
>
> This patch should be first patch.
I can shuffle it of course!
> The below what planned commit message in my local tree.
Okay, so you focused on runtime PM handling. Not quite sure if I can
test this feature with the SDMA engine. I also have limited time for
this feature.
Is it okay for you and the DMA maintainers to add the runtime PM feature
as separate patch (provided by NXP/Frank)?
> Implementing runtime PM for DMA channels is challenging. If a channel
> resumes at allocation and suspends at free, the DMA engine often remains on
> because most drivers request a channel at probe.
>
> Tracking the number of pending DMA descriptors is also problematic, as some
> consumers append new descriptors in atomic contexts, such as IRQ handlers,
> where runtime resume cannot be called.
>
> Using a device link simplifies this issue. If a consumer requires data
> transfer, it must be in a runtime-resumed state, ensuring that the DMA
> channel is also active by device link. This allows safe operations, like
> appending new descriptors. Conversely, when the consumer no longer requires
> data transfer, both it and the supplier (DMA channel) can enter a suspended
> state if no other consumer is using it.
>
> Introduce the `create_link` flag to enable this feature.
>
> also suggest add create_link flag to enable this feature in case some
> side impact to other dma-engine. After some time test, we can enable it
> default.
What regressions do you have in mind? I wouldn't hide the feature behind
a flag because this may slow done the convert process, because no one is
interessted in, or has no time for testing, ...
> > drivers/dma/dmaengine.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > --- a/drivers/dma/dmaengine.c
> > +++ b/drivers/dma/dmaengine.c
> > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > struct dma_device *d, *_d;
> > struct dma_chan *chan = NULL;
> > + struct device_link *dl;
> >
> > if (is_of_node(fwnode))
> > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > /* No functional issue if it fails, users are supposed to test before use */
> > #endif
> >
> > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
>
> chan->device->dev is dmaengine devices. But some dmaengine's each channel
> have device, consumer should link to chan's device, not dmaengine device
> because some dmaengine support per channel clock\power management.
I get your point. Can you give me some pointers please? To me it seems
like the dma_chan_dev is only used for sysfs purpose according the
dmaengine.h.
> chan's device's parent devices is dmaengine devices. it should also work
> for sdma case
I see, this must be tested of course.
> if (chan->device->create_devlink) {
> u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
According device_link.rst: using DL_FLAG_STATELESS and
DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> if (pm_runtime_active(dev))
> flags |= DL_FLAG_RPM_ACTIVE;
This is of course interessting, thanks for the hint.
> When create device link (apply channel), consume may active.
I have read it as: "resue the supplier and ensure that the supplier
follows the consumer runtime state".
> dl = device_link_add(chan->slave, &chan->dev->device, flags);
Huh.. you used the dmaengine device too?
Regards,
Marco
> }
>
> Need update kernel doc
>
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index bb146c5ac3e4c..ffb3a8f0070ba 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -323,7 +323,8 @@ struct dma_router {
> * @cookie: last cookie value returned to client
> * @completed_cookie: last completed cookie for this channel
> * @chan_id: channel ID for sysfs
> - * @dev: class device for sysfs
> + * @dev: class device for sysfs, also use for pre channel runtime pm and
> + * use custom/different dma-mapping
>
> Frank
>
>
> > + if (!dl) {
> > + dev_err(dev, "failed to create device link to %s\n",
> > + dev_name(chan->device->dev));
> > + return ERR_PTR(-EINVAL);
> > + }
> > chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
> > if (!chan->name)
> > return chan;
> >
> > --
> > 2.47.2
> >
>
On Tue, Sep 09, 2025 at 02:03:09PM +0200, Marco Felsch wrote:
> Hi Frank,
>
> On 25-09-03, Frank Li wrote:
> > On Wed, Sep 03, 2025 at 03:06:17PM +0200, Marco Felsch wrote:
> > > Add support to create device_links between dmaengine suppliers and the
> > > dma consumers. This shifts the device dep-chain teardown/bringup logic
> > > to the driver core.
> > >
> > > Moving this to the core allows the dmaengine drivers to simplify the
> > > .remove() hooks and also to ensure that no dmaengine driver is ever
> > > removed before the consumer is removed.
> > >
> > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > ---
> >
> > Thank you work for devlink between dmaengine and devices. I have similar
> > idea.
> >
> > This patch should be first patch.
>
> I can shuffle it of course!
>
> > The below what planned commit message in my local tree.
>
> Okay, so you focused on runtime PM handling. Not quite sure if I can
> test this feature with the SDMA engine. I also have limited time for
> this feature.
>
> Is it okay for you and the DMA maintainers to add the runtime PM feature
> as separate patch (provided by NXP/Frank)?
we can support runtime pm later.
>
> > Implementing runtime PM for DMA channels is challenging. If a channel
> > resumes at allocation and suspends at free, the DMA engine often remains on
> > because most drivers request a channel at probe.
> >
> > Tracking the number of pending DMA descriptors is also problematic, as some
> > consumers append new descriptors in atomic contexts, such as IRQ handlers,
> > where runtime resume cannot be called.
> >
> > Using a device link simplifies this issue. If a consumer requires data
> > transfer, it must be in a runtime-resumed state, ensuring that the DMA
> > channel is also active by device link. This allows safe operations, like
> > appending new descriptors. Conversely, when the consumer no longer requires
> > data transfer, both it and the supplier (DMA channel) can enter a suspended
> > state if no other consumer is using it.
> >
> > Introduce the `create_link` flag to enable this feature.
> >
> > also suggest add create_link flag to enable this feature in case some
> > side impact to other dma-engine. After some time test, we can enable it
> > default.
>
> What regressions do you have in mind? I wouldn't hide the feature behind
> a flag because this may slow done the convert process, because no one is
> interessted in, or has no time for testing, ...
Unlike other devices, like phys, regulator, mailbox..., which auto create
devlink at probe. I am not clear why dma skip this one. So I think there
should be some reason behind. Maybe other people, rob or Vinod Koul know
the reason.
static const struct supplier_bindings of_supplier_bindings[] = {
...
{ .parse_prop = parse_dmas, .optional = true, },
If remove "optional = true", devlink will auto create. I am not sure why
set true here.
>
> > > drivers/dma/dmaengine.c | 8 ++++++++
> > > 1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > --- a/drivers/dma/dmaengine.c
> > > +++ b/drivers/dma/dmaengine.c
> > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > struct dma_device *d, *_d;
> > > struct dma_chan *chan = NULL;
> > > + struct device_link *dl;
> > >
> > > if (is_of_node(fwnode))
> > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > /* No functional issue if it fails, users are supposed to test before use */
> > > #endif
> > >
> > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> >
> > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > have device, consumer should link to chan's device, not dmaengine device
> > because some dmaengine support per channel clock\power management.
>
> I get your point. Can you give me some pointers please? To me it seems
> like the dma_chan_dev is only used for sysfs purpose according the
> dmaengine.h.
Not really, there are other dma engineer already reuse it for other purpose.
So It needs update kernel doc for dma_chan_dev.
>
> > chan's device's parent devices is dmaengine devices. it should also work
> > for sdma case
>
> I see, this must be tested of course.
> > > if (chan->device->create_devlink) {
> > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
>
> According device_link.rst: using DL_FLAG_STATELESS and
> DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
>
> > if (pm_runtime_active(dev))
> > flags |= DL_FLAG_RPM_ACTIVE;
>
> This is of course interessting, thanks for the hint.
>
> > When create device link (apply channel), consume may active.
>
> I have read it as: "resue the supplier and ensure that the supplier
> follows the consumer runtime state".
>
> > dl = device_link_add(chan->slave, &chan->dev->device, flags);
>
> Huh.. you used the dmaengine device too?
/**
* struct dma_chan_dev - relate sysfs device node to backing channel device
* @chan: driver channel device
* @device: sysfs device
* @dev_id: parent dma_device dev_id
* @chan_dma_dev: The channel is using custom/different dma-mapping
* compared to the parent dma_device
*/
struct dma_chan_dev {
struct dma_chan *chan;
struct device device;
int dev_id;
bool chan_dma_dev;
};
struct dma_chan {
struct dma_device *device; /// this one should be dmaengine
struct dma_chan_dev *dev; /// this one is pre-chan device.
}
Frank
>
> Regards,
> Marco
>
>
> > }
> >
> > Need update kernel doc
> >
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index bb146c5ac3e4c..ffb3a8f0070ba 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -323,7 +323,8 @@ struct dma_router {
> > * @cookie: last cookie value returned to client
> > * @completed_cookie: last completed cookie for this channel
> > * @chan_id: channel ID for sysfs
> > - * @dev: class device for sysfs
> > + * @dev: class device for sysfs, also use for pre channel runtime pm and
> > + * use custom/different dma-mapping
> >
> > Frank
> >
> >
> > > + if (!dl) {
> > > + dev_err(dev, "failed to create device link to %s\n",
> > > + dev_name(chan->device->dev));
> > > + return ERR_PTR(-EINVAL);
> > > + }
> > > chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
> > > if (!chan->name)
> > > return chan;
> > >
> > > --
> > > 2.47.2
> > >
> >
On 25-09-09, Frank Li wrote:
...
> > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > --- a/drivers/dma/dmaengine.c
> > > > +++ b/drivers/dma/dmaengine.c
> > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > struct dma_device *d, *_d;
> > > > struct dma_chan *chan = NULL;
> > > > + struct device_link *dl;
> > > >
> > > > if (is_of_node(fwnode))
> > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > #endif
> > > >
> > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > >
> > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > have device, consumer should link to chan's device, not dmaengine device
> > > because some dmaengine support per channel clock\power management.
> >
> > I get your point. Can you give me some pointers please? To me it seems
> > like the dma_chan_dev is only used for sysfs purpose according the
> > dmaengine.h.
>
> Not really, there are other dma engineer already reuse it for other purpose.
> So It needs update kernel doc for dma_chan_dev.
Can you please provide me some pointers? I checked the kernel code base
for the struct::dma_chan_dev. I didn't found any references within the
dmaengine drivers. The only usage I found was for the sysfs purpose.
> > > chan's device's parent devices is dmaengine devices. it should also work
> > > for sdma case
> >
> > I see, this must be tested of course.
> > > > if (chan->device->create_devlink) {
> > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> >
> > According device_link.rst: using DL_FLAG_STATELESS and
> > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> >
> > > if (pm_runtime_active(dev))
> > > flags |= DL_FLAG_RPM_ACTIVE;
> >
> > This is of course interessting, thanks for the hint.
> >
> > > When create device link (apply channel), consume may active.
> >
> > I have read it as: "resue the supplier and ensure that the supplier
> > follows the consumer runtime state".
> >
> > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> >
> > Huh.. you used the dmaengine device too?
>
> /**
> * struct dma_chan_dev - relate sysfs device node to backing channel device
> * @chan: driver channel device
> * @device: sysfs device
> * @dev_id: parent dma_device dev_id
> * @chan_dma_dev: The channel is using custom/different dma-mapping
> * compared to the parent dma_device
> */
> struct dma_chan_dev {
> struct dma_chan *chan;
> struct device device;
> int dev_id;
> bool chan_dma_dev;
> };
>
> struct dma_chan {
> struct dma_device *device; /// this one should be dmaengine
> struct dma_chan_dev *dev; /// this one is pre-chan device.
> }
I've tested your approach but it turns out that teh dma_chan_dev has no
driver. Of course we could use the DL_FLAG_STATELESS flag but this is
described as:
| When driver presence on the supplier is irrelevant and only correct
| suspend/resume and shutdown ordering is needed, the device link may
| simply be set up with the ``DL_FLAG_STATELESS`` flag. In other words,
| enforcing driver presence on the supplier is optional.
I want to enforce the driver presence, therefore I used the manged flags
which excludes the DL_FLAG_STATELESS, if I get it right.
Please see the below the debug output:
** use the dmaengine device as supplier **
device_link_init_status: supplier.dev:30bd0000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
device_link_init_status: supplier.dev:30e10000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30c20000.sai consumer.drv:fsl-sai consumer.status:0x1
** use the dma channel device as supplier **
device_link_init_status: supplier.dev:dma0chan0 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
device_link_init_status: supplier.dev:dma0chan1 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
------------[ cut here ]------------
WARNING: CPU: 0 PID: 51 at /drivers/base/core.c:1387 device_links_driver_bound+0x170/0x3a0
...
---[ end trace 0000000000000000 ]---
------------[ cut here ]------------
As said, I get your point regarding the usage of the dma-channel device
but I didn't found any reference to a driver which used the dma-channel
device. Also since I want to have the supply driver to enforced by the
devlink I don't want to use the DL_FLAG_STATELESS flag.
Regarding your point, that some DMA controllers may have seperate clocks
for each channel: I think this can be handled by the dmaengine driver,
e.g. via the device_alloc_chan_resources() hook.
@all
I'm pleased about any input :)
Regards,
Marco
On Wed, Sep 10, 2025 at 09:35:45PM +0200, Marco Felsch wrote:
> On 25-09-09, Frank Li wrote:
>
> ...
>
> > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > > --- a/drivers/dma/dmaengine.c
> > > > > +++ b/drivers/dma/dmaengine.c
> > > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > struct dma_device *d, *_d;
> > > > > struct dma_chan *chan = NULL;
> > > > > + struct device_link *dl;
> > > > >
> > > > > if (is_of_node(fwnode))
> > > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > > #endif
> > > > >
> > > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > >
> > > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > > have device, consumer should link to chan's device, not dmaengine device
> > > > because some dmaengine support per channel clock\power management.
> > >
> > > I get your point. Can you give me some pointers please? To me it seems
> > > like the dma_chan_dev is only used for sysfs purpose according the
> > > dmaengine.h.
> >
> > Not really, there are other dma engineer already reuse it for other purpose.
> > So It needs update kernel doc for dma_chan_dev.
>
> Can you please provide me some pointers? I checked the kernel code base
> for the struct::dma_chan_dev. I didn't found any references within the
> dmaengine drivers. The only usage I found was for the sysfs purpose.
static void k3_configure_chan_coherency(struct dma_chan *chan, u32 asel)
{
struct device *chan_dev = &chan->dev->device;
...
}
>
> > > > chan's device's parent devices is dmaengine devices. it should also work
> > > > for sdma case
> > >
> > > I see, this must be tested of course.
> > > > > if (chan->device->create_devlink) {
> > > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> > >
> > > According device_link.rst: using DL_FLAG_STATELESS and
> > > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> > >
> > > > if (pm_runtime_active(dev))
> > > > flags |= DL_FLAG_RPM_ACTIVE;
> > >
> > > This is of course interessting, thanks for the hint.
> > >
> > > > When create device link (apply channel), consume may active.
> > >
> > > I have read it as: "resue the supplier and ensure that the supplier
> > > follows the consumer runtime state".
> > >
> > > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> > >
> > > Huh.. you used the dmaengine device too?
> >
> > /**
> > * struct dma_chan_dev - relate sysfs device node to backing channel device
> > * @chan: driver channel device
> > * @device: sysfs device
> > * @dev_id: parent dma_device dev_id
> > * @chan_dma_dev: The channel is using custom/different dma-mapping
> > * compared to the parent dma_device
> > */
> > struct dma_chan_dev {
> > struct dma_chan *chan;
> > struct device device;
> > int dev_id;
> > bool chan_dma_dev;
> > };
> >
> > struct dma_chan {
> > struct dma_device *device; /// this one should be dmaengine
> > struct dma_chan_dev *dev; /// this one is pre-chan device.
> > }
>
> I've tested your approach but it turns out that teh dma_chan_dev has no
> driver. Of course we could use the DL_FLAG_STATELESS flag but this is
> described as:
>
> | When driver presence on the supplier is irrelevant and only correct
> | suspend/resume and shutdown ordering is needed, the device link may
> | simply be set up with the ``DL_FLAG_STATELESS`` flag. In other words,
> | enforcing driver presence on the supplier is optional.
>
> I want to enforce the driver presence, therefore I used the manged flags
> which excludes the DL_FLAG_STATELESS, if I get it right.
>
> Please see the below the debug output:
>
> ** use the dmaengine device as supplier **
>
> device_link_init_status: supplier.dev:30bd0000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> device_link_init_status: supplier.dev:30e10000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30c20000.sai consumer.drv:fsl-sai consumer.status:0x1
>
>
> ** use the dma channel device as supplier **
>
> device_link_init_status: supplier.dev:dma0chan0 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> device_link_init_status: supplier.dev:dma0chan1 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
It should be similar with phy drivers, which phy_create() create individual
phy devices (like dma channel devices).
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 51 at /drivers/base/core.c:1387 device_links_driver_bound+0x170/0x3a0
> ...
> ---[ end trace 0000000000000000 ]---
> ------------[ cut here ]------------
>
> As said, I get your point regarding the usage of the dma-channel device
> but I didn't found any reference to a driver which used the dma-channel
> device. Also since I want to have the supply driver to enforced by the
> devlink I don't want to use the DL_FLAG_STATELESS flag.
Maybe add DL_FLAG, link to parent's device driver. Need some time to
investigate more. PHY driver should good example to refer to.
>
> Regarding your point, that some DMA controllers may have seperate clocks
> for each channel: I think this can be handled by the dmaengine driver,
> e.g. via the device_alloc_chan_resources() hook.
device_alloc_chan_resources() is not efficient enough, most driver allocate
channel at probe, so clk of this channel will be always on. ideally, only
when consumer devices is runtime resume state, turn on dma channel clock.
Frank
>
> @all
> I'm pleased about any input :)
>
> Regards,
> Marco
On 25-09-10, Frank Li wrote:
> On Wed, Sep 10, 2025 at 09:35:45PM +0200, Marco Felsch wrote:
> > On 25-09-09, Frank Li wrote:
> >
> > ...
> >
> > > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > > > --- a/drivers/dma/dmaengine.c
> > > > > > +++ b/drivers/dma/dmaengine.c
> > > > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > > struct dma_device *d, *_d;
> > > > > > struct dma_chan *chan = NULL;
> > > > > > + struct device_link *dl;
> > > > > >
> > > > > > if (is_of_node(fwnode))
> > > > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > > > #endif
> > > > > >
> > > > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > >
> > > > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > > > have device, consumer should link to chan's device, not dmaengine device
> > > > > because some dmaengine support per channel clock\power management.
> > > >
> > > > I get your point. Can you give me some pointers please? To me it seems
> > > > like the dma_chan_dev is only used for sysfs purpose according the
> > > > dmaengine.h.
> > >
> > > Not really, there are other dma engineer already reuse it for other purpose.
> > > So It needs update kernel doc for dma_chan_dev.
> >
> > Can you please provide me some pointers? I checked the kernel code base
> > for the struct::dma_chan_dev. I didn't found any references within the
> > dmaengine drivers. The only usage I found was for the sysfs purpose.
>
> static void k3_configure_chan_coherency(struct dma_chan *chan, u32 asel)
> {
> struct device *chan_dev = &chan->dev->device;
> ...
> }
>
> >
> > > > > chan's device's parent devices is dmaengine devices. it should also work
> > > > > for sdma case
> > > >
> > > > I see, this must be tested of course.
> > > > > > if (chan->device->create_devlink) {
> > > > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> > > >
> > > > According device_link.rst: using DL_FLAG_STATELESS and
> > > > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> > > >
> > > > > if (pm_runtime_active(dev))
> > > > > flags |= DL_FLAG_RPM_ACTIVE;
> > > >
> > > > This is of course interessting, thanks for the hint.
> > > >
> > > > > When create device link (apply channel), consume may active.
> > > >
> > > > I have read it as: "resue the supplier and ensure that the supplier
> > > > follows the consumer runtime state".
> > > >
> > > > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> > > >
> > > > Huh.. you used the dmaengine device too?
> > >
> > > /**
> > > * struct dma_chan_dev - relate sysfs device node to backing channel device
> > > * @chan: driver channel device
> > > * @device: sysfs device
> > > * @dev_id: parent dma_device dev_id
> > > * @chan_dma_dev: The channel is using custom/different dma-mapping
> > > * compared to the parent dma_device
> > > */
> > > struct dma_chan_dev {
> > > struct dma_chan *chan;
> > > struct device device;
> > > int dev_id;
> > > bool chan_dma_dev;
> > > };
> > >
> > > struct dma_chan {
> > > struct dma_device *device; /// this one should be dmaengine
> > > struct dma_chan_dev *dev; /// this one is pre-chan device.
> > > }
> >
> > I've tested your approach but it turns out that teh dma_chan_dev has no
> > driver. Of course we could use the DL_FLAG_STATELESS flag but this is
> > described as:
> >
> > | When driver presence on the supplier is irrelevant and only correct
> > | suspend/resume and shutdown ordering is needed, the device link may
> > | simply be set up with the ``DL_FLAG_STATELESS`` flag. In other words,
> > | enforcing driver presence on the supplier is optional.
> >
> > I want to enforce the driver presence, therefore I used the manged flags
> > which excludes the DL_FLAG_STATELESS, if I get it right.
> >
> > Please see the below the debug output:
> >
> > ** use the dmaengine device as supplier **
> >
> > device_link_init_status: supplier.dev:30bd0000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > device_link_init_status: supplier.dev:30e10000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30c20000.sai consumer.drv:fsl-sai consumer.status:0x1
> >
> >
> > ** use the dma channel device as supplier **
> >
> > device_link_init_status: supplier.dev:dma0chan0 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > device_link_init_status: supplier.dev:dma0chan1 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
>
> It should be similar with phy drivers, which phy_create() create individual
> phy devices (like dma channel devices).
Unfortunately phy drivers do use the DL_FLAG_STATELESS mechanism. My
main goal was to have managed links to overcome the current situation:
dmaengine drivers can be removed without removing the consumer drivers
first.
You have a valid point by making use dma-channel devices ( dma<X>cha<Y>)
to manage suspend/resume, as well as runtime-PM for each channel.
But I see this rather as an addition to my solution because these links
must be stateless and stateless/unmanaged links don't guarantee the
correct remove order (my main goal).
That beeing said, I'm not sure how you want to handle the clock/power
enablement per channel-device. This would require additional work on the
dma_devclass to add a proper .pm hook else the PM and runtime-PM calls
are only forwarded to the parent dmaengine driver. On this level the
dmaengine driver has no knowledge which channel is going to be
enabled/disabled.
In conclusion, I see my approach as valid to ensure the correct remove
order. Your suggestion is valid and can be added later on too since this
needs more work to have a proper per-channel runtime-PM.
Regards,
Marco
>
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 51 at /drivers/base/core.c:1387 device_links_driver_bound+0x170/0x3a0
> > ...
> > ---[ end trace 0000000000000000 ]---
> > ------------[ cut here ]------------
> >
> > As said, I get your point regarding the usage of the dma-channel device
> > but I didn't found any reference to a driver which used the dma-channel
> > device. Also since I want to have the supply driver to enforced by the
> > devlink I don't want to use the DL_FLAG_STATELESS flag.
>
> Maybe add DL_FLAG, link to parent's device driver. Need some time to
> investigate more. PHY driver should good example to refer to.
>
> >
> > Regarding your point, that some DMA controllers may have seperate clocks
> > for each channel: I think this can be handled by the dmaengine driver,
> > e.g. via the device_alloc_chan_resources() hook.
>
> device_alloc_chan_resources() is not efficient enough, most driver allocate
> channel at probe, so clk of this channel will be always on. ideally, only
> when consumer devices is runtime resume state, turn on dma channel clock.
>
> Frank
> >
> > @all
> > I'm pleased about any input :)
> >
> > Regards,
> > Marco
>
On Thu, Sep 11, 2025 at 01:50:56PM +0200, Marco Felsch wrote:
> On 25-09-10, Frank Li wrote:
> > On Wed, Sep 10, 2025 at 09:35:45PM +0200, Marco Felsch wrote:
> > > On 25-09-09, Frank Li wrote:
> > >
> > > ...
> > >
> > > > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > > > > --- a/drivers/dma/dmaengine.c
> > > > > > > +++ b/drivers/dma/dmaengine.c
> > > > > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > > > struct dma_device *d, *_d;
> > > > > > > struct dma_chan *chan = NULL;
> > > > > > > + struct device_link *dl;
> > > > > > >
> > > > > > > if (is_of_node(fwnode))
> > > > > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > > > > #endif
> > > > > > >
> > > > > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > > >
> > > > > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > > > > have device, consumer should link to chan's device, not dmaengine device
> > > > > > because some dmaengine support per channel clock\power management.
> > > > >
> > > > > I get your point. Can you give me some pointers please? To me it seems
> > > > > like the dma_chan_dev is only used for sysfs purpose according the
> > > > > dmaengine.h.
> > > >
> > > > Not really, there are other dma engineer already reuse it for other purpose.
> > > > So It needs update kernel doc for dma_chan_dev.
> > >
> > > Can you please provide me some pointers? I checked the kernel code base
> > > for the struct::dma_chan_dev. I didn't found any references within the
> > > dmaengine drivers. The only usage I found was for the sysfs purpose.
> >
> > static void k3_configure_chan_coherency(struct dma_chan *chan, u32 asel)
> > {
> > struct device *chan_dev = &chan->dev->device;
> > ...
> > }
> >
> > >
> > > > > > chan's device's parent devices is dmaengine devices. it should also work
> > > > > > for sdma case
> > > > >
> > > > > I see, this must be tested of course.
> > > > > > > if (chan->device->create_devlink) {
> > > > > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> > > > >
> > > > > According device_link.rst: using DL_FLAG_STATELESS and
> > > > > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> > > > >
> > > > > > if (pm_runtime_active(dev))
> > > > > > flags |= DL_FLAG_RPM_ACTIVE;
> > > > >
> > > > > This is of course interessting, thanks for the hint.
> > > > >
> > > > > > When create device link (apply channel), consume may active.
> > > > >
> > > > > I have read it as: "resue the supplier and ensure that the supplier
> > > > > follows the consumer runtime state".
> > > > >
> > > > > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> > > > >
> > > > > Huh.. you used the dmaengine device too?
> > > >
> > > > /**
> > > > * struct dma_chan_dev - relate sysfs device node to backing channel device
> > > > * @chan: driver channel device
> > > > * @device: sysfs device
> > > > * @dev_id: parent dma_device dev_id
> > > > * @chan_dma_dev: The channel is using custom/different dma-mapping
> > > > * compared to the parent dma_device
> > > > */
> > > > struct dma_chan_dev {
> > > > struct dma_chan *chan;
> > > > struct device device;
> > > > int dev_id;
> > > > bool chan_dma_dev;
> > > > };
> > > >
> > > > struct dma_chan {
> > > > struct dma_device *device; /// this one should be dmaengine
> > > > struct dma_chan_dev *dev; /// this one is pre-chan device.
> > > > }
> > >
> > > I've tested your approach but it turns out that teh dma_chan_dev has no
> > > driver. Of course we could use the DL_FLAG_STATELESS flag but this is
> > > described as:
> > >
> > > | When driver presence on the supplier is irrelevant and only correct
> > > | suspend/resume and shutdown ordering is needed, the device link may
> > > | simply be set up with the ``DL_FLAG_STATELESS`` flag. In other words,
> > > | enforcing driver presence on the supplier is optional.
> > >
> > > I want to enforce the driver presence, therefore I used the manged flags
> > > which excludes the DL_FLAG_STATELESS, if I get it right.
> > >
> > > Please see the below the debug output:
> > >
> > > ** use the dmaengine device as supplier **
> > >
> > > device_link_init_status: supplier.dev:30bd0000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > > device_link_init_status: supplier.dev:30e10000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30c20000.sai consumer.drv:fsl-sai consumer.status:0x1
> > >
> > >
> > > ** use the dma channel device as supplier **
> > >
> > > device_link_init_status: supplier.dev:dma0chan0 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > > device_link_init_status: supplier.dev:dma0chan1 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> >
> > It should be similar with phy drivers, which phy_create() create individual
> > phy devices (like dma channel devices).
>
> Unfortunately phy drivers do use the DL_FLAG_STATELESS mechanism. My
> main goal was to have managed links to overcome the current situation:
> dmaengine drivers can be removed without removing the consumer drivers
> first.
>
> You have a valid point by making use dma-channel devices ( dma<X>cha<Y>)
> to manage suspend/resume, as well as runtime-PM for each channel.
>
> But I see this rather as an addition to my solution because these links
> must be stateless and stateless/unmanaged links don't guarantee the
> correct remove order (my main goal).
If that, phy should have simiar problems. It should be resolved at higher
layer to avoid fix this kinds of problem one by one.
>
> That beeing said, I'm not sure how you want to handle the clock/power
> enablement per channel-device. This would require additional work on the
> dma_devclass to add a proper .pm hook else the PM and runtime-PM calls
> are only forwarded to the parent dmaengine driver. On this level the
> dmaengine driver has no knowledge which channel is going to be
> enabled/disabled.
I have draft runtime pm patch for eDMA.
>
> In conclusion, I see my approach as valid to ensure the correct remove
> order. Your suggestion is valid and can be added later on too since this
> needs more work to have a proper per-channel runtime-PM.
We need pave a good road. This part is common dma-engine, which is worth to
do good solution.
Frank
>
> Regards,
> Marco
>
> >
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 51 at /drivers/base/core.c:1387 device_links_driver_bound+0x170/0x3a0
> > > ...
> > > ---[ end trace 0000000000000000 ]---
> > > ------------[ cut here ]------------
> > >
> > > As said, I get your point regarding the usage of the dma-channel device
> > > but I didn't found any reference to a driver which used the dma-channel
> > > device. Also since I want to have the supply driver to enforced by the
> > > devlink I don't want to use the DL_FLAG_STATELESS flag.
> >
> > Maybe add DL_FLAG, link to parent's device driver. Need some time to
> > investigate more. PHY driver should good example to refer to.
> >
> > >
> > > Regarding your point, that some DMA controllers may have seperate clocks
> > > for each channel: I think this can be handled by the dmaengine driver,
> > > e.g. via the device_alloc_chan_resources() hook.
> >
> > device_alloc_chan_resources() is not efficient enough, most driver allocate
> > channel at probe, so clk of this channel will be always on. ideally, only
> > when consumer devices is runtime resume state, turn on dma channel clock.
> >
> > Frank
> > >
> > > @all
> > > I'm pleased about any input :)
> > >
> > > Regards,
> > > Marco
> >
On 25-09-11, Frank Li wrote:
> On Thu, Sep 11, 2025 at 01:50:56PM +0200, Marco Felsch wrote:
> > On 25-09-10, Frank Li wrote:
> > > On Wed, Sep 10, 2025 at 09:35:45PM +0200, Marco Felsch wrote:
> > > > On 25-09-09, Frank Li wrote:
> > > >
> > > > ...
> > > >
> > > > > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > > > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > > > > > --- a/drivers/dma/dmaengine.c
> > > > > > > > +++ b/drivers/dma/dmaengine.c
> > > > > > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > > > > struct dma_device *d, *_d;
> > > > > > > > struct dma_chan *chan = NULL;
> > > > > > > > + struct device_link *dl;
> > > > > > > >
> > > > > > > > if (is_of_node(fwnode))
> > > > > > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > > > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > > > > > #endif
> > > > > > > >
> > > > > > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > > > >
> > > > > > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > > > > > have device, consumer should link to chan's device, not dmaengine device
> > > > > > > because some dmaengine support per channel clock\power management.
> > > > > >
> > > > > > I get your point. Can you give me some pointers please? To me it seems
> > > > > > like the dma_chan_dev is only used for sysfs purpose according the
> > > > > > dmaengine.h.
> > > > >
> > > > > Not really, there are other dma engineer already reuse it for other purpose.
> > > > > So It needs update kernel doc for dma_chan_dev.
> > > >
> > > > Can you please provide me some pointers? I checked the kernel code base
> > > > for the struct::dma_chan_dev. I didn't found any references within the
> > > > dmaengine drivers. The only usage I found was for the sysfs purpose.
> > >
> > > static void k3_configure_chan_coherency(struct dma_chan *chan, u32 asel)
> > > {
> > > struct device *chan_dev = &chan->dev->device;
> > > ...
> > > }
> > >
> > > >
> > > > > > > chan's device's parent devices is dmaengine devices. it should also work
> > > > > > > for sdma case
> > > > > >
> > > > > > I see, this must be tested of course.
> > > > > > > > if (chan->device->create_devlink) {
> > > > > > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> > > > > >
> > > > > > According device_link.rst: using DL_FLAG_STATELESS and
> > > > > > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> > > > > >
> > > > > > > if (pm_runtime_active(dev))
> > > > > > > flags |= DL_FLAG_RPM_ACTIVE;
> > > > > >
> > > > > > This is of course interessting, thanks for the hint.
> > > > > >
> > > > > > > When create device link (apply channel), consume may active.
> > > > > >
> > > > > > I have read it as: "resue the supplier and ensure that the supplier
> > > > > > follows the consumer runtime state".
> > > > > >
> > > > > > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> > > > > >
> > > > > > Huh.. you used the dmaengine device too?
> > > > >
> > > > > /**
> > > > > * struct dma_chan_dev - relate sysfs device node to backing channel device
> > > > > * @chan: driver channel device
> > > > > * @device: sysfs device
> > > > > * @dev_id: parent dma_device dev_id
> > > > > * @chan_dma_dev: The channel is using custom/different dma-mapping
> > > > > * compared to the parent dma_device
> > > > > */
> > > > > struct dma_chan_dev {
> > > > > struct dma_chan *chan;
> > > > > struct device device;
> > > > > int dev_id;
> > > > > bool chan_dma_dev;
> > > > > };
> > > > >
> > > > > struct dma_chan {
> > > > > struct dma_device *device; /// this one should be dmaengine
> > > > > struct dma_chan_dev *dev; /// this one is pre-chan device.
> > > > > }
> > > >
> > > > I've tested your approach but it turns out that teh dma_chan_dev has no
> > > > driver. Of course we could use the DL_FLAG_STATELESS flag but this is
> > > > described as:
> > > >
> > > > | When driver presence on the supplier is irrelevant and only correct
> > > > | suspend/resume and shutdown ordering is needed, the device link may
> > > > | simply be set up with the ``DL_FLAG_STATELESS`` flag. In other words,
> > > > | enforcing driver presence on the supplier is optional.
> > > >
> > > > I want to enforce the driver presence, therefore I used the manged flags
> > > > which excludes the DL_FLAG_STATELESS, if I get it right.
> > > >
> > > > Please see the below the debug output:
> > > >
> > > > ** use the dmaengine device as supplier **
> > > >
> > > > device_link_init_status: supplier.dev:30bd0000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > > > device_link_init_status: supplier.dev:30e10000.dma-controller supplier.drv:imx-sdma supplier.status:0x2 consumer:dev:30c20000.sai consumer.drv:fsl-sai consumer.status:0x1
> > > >
> > > >
> > > > ** use the dma channel device as supplier **
> > > >
> > > > device_link_init_status: supplier.dev:dma0chan0 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > > > device_link_init_status: supplier.dev:dma0chan1 supplier.drv:no-driver supplier.status:0x0 consumer:dev:30840000.spi consumer.drv:spi_imx consumer.status:0x1
> > >
> > > It should be similar with phy drivers, which phy_create() create individual
> > > phy devices (like dma channel devices).
> >
> > Unfortunately phy drivers do use the DL_FLAG_STATELESS mechanism. My
> > main goal was to have managed links to overcome the current situation:
> > dmaengine drivers can be removed without removing the consumer drivers
> > first.
> >
> > You have a valid point by making use dma-channel devices ( dma<X>cha<Y>)
> > to manage suspend/resume, as well as runtime-PM for each channel.
> >
> > But I see this rather as an addition to my solution because these links
> > must be stateless and stateless/unmanaged links don't guarantee the
> > correct remove order (my main goal).
>
> If that, phy should have simiar problems. It should be resolved at higher
> layer to avoid fix this kinds of problem one by one.
I'm not sure because the devlink API is more or less clear about STATELESS
links. So phy should rather consider using managed links if they want to
ensure this.
> > That beeing said, I'm not sure how you want to handle the clock/power
> > enablement per channel-device. This would require additional work on the
> > dma_devclass to add a proper .pm hook else the PM and runtime-PM calls
> > are only forwarded to the parent dmaengine driver. On this level the
> > dmaengine driver has no knowledge which channel is going to be
> > enabled/disabled.
>
> I have draft runtime pm patch for eDMA.
>
> >
> > In conclusion, I see my approach as valid to ensure the correct remove
> > order. Your suggestion is valid and can be added later on too since this
> > needs more work to have a proper per-channel runtime-PM.
>
> We need pave a good road. This part is common dma-engine, which is worth to
> do good solution.
+1
I will send a new v2 which split the devlink patches (common part and
the imx-sdma part) from the rest of this series. This decouples most of
the the imx-sdma cleanup from the devlink discussion and we can continue
there.
Regards,
Marco
On 25-09-09, Frank Li wrote:
> On Tue, Sep 09, 2025 at 02:03:09PM +0200, Marco Felsch wrote:
> > Hi Frank,
> >
> > On 25-09-03, Frank Li wrote:
> > > On Wed, Sep 03, 2025 at 03:06:17PM +0200, Marco Felsch wrote:
> > > > Add support to create device_links between dmaengine suppliers and the
> > > > dma consumers. This shifts the device dep-chain teardown/bringup logic
> > > > to the driver core.
> > > >
> > > > Moving this to the core allows the dmaengine drivers to simplify the
> > > > .remove() hooks and also to ensure that no dmaengine driver is ever
> > > > removed before the consumer is removed.
> > > >
> > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > > ---
> > >
> > > Thank you work for devlink between dmaengine and devices. I have similar
> > > idea.
> > >
> > > This patch should be first patch.
> >
> > I can shuffle it of course!
> >
> > > The below what planned commit message in my local tree.
> >
> > Okay, so you focused on runtime PM handling. Not quite sure if I can
> > test this feature with the SDMA engine. I also have limited time for
> > this feature.
> >
> > Is it okay for you and the DMA maintainers to add the runtime PM feature
> > as separate patch (provided by NXP/Frank)?
>
> we can support runtime pm later.
>
> >
> > > Implementing runtime PM for DMA channels is challenging. If a channel
> > > resumes at allocation and suspends at free, the DMA engine often remains on
> > > because most drivers request a channel at probe.
> > >
> > > Tracking the number of pending DMA descriptors is also problematic, as some
> > > consumers append new descriptors in atomic contexts, such as IRQ handlers,
> > > where runtime resume cannot be called.
> > >
> > > Using a device link simplifies this issue. If a consumer requires data
> > > transfer, it must be in a runtime-resumed state, ensuring that the DMA
> > > channel is also active by device link. This allows safe operations, like
> > > appending new descriptors. Conversely, when the consumer no longer requires
> > > data transfer, both it and the supplier (DMA channel) can enter a suspended
> > > state if no other consumer is using it.
> > >
> > > Introduce the `create_link` flag to enable this feature.
> > >
> > > also suggest add create_link flag to enable this feature in case some
> > > side impact to other dma-engine. After some time test, we can enable it
> > > default.
> >
> > What regressions do you have in mind? I wouldn't hide the feature behind
> > a flag because this may slow done the convert process, because no one is
> > interessted in, or has no time for testing, ...
>
> Unlike other devices, like phys, regulator, mailbox..., which auto create
> devlink at probe. I am not clear why dma skip this one. So I think there
> should be some reason behind. Maybe other people, rob or Vinod Koul know
> the reason.
>
> static const struct supplier_bindings of_supplier_bindings[] = {
> ...
> { .parse_prop = parse_dmas, .optional = true, },
>
> If remove "optional = true", devlink will auto create. I am not sure why
> set true here.
I've seen this too. Could be because DMA controllers + users aren't OF
related and therefore should be handled within the framework itself.
> > > > drivers/dma/dmaengine.c | 8 ++++++++
> > > > 1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > --- a/drivers/dma/dmaengine.c
> > > > +++ b/drivers/dma/dmaengine.c
> > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > struct dma_device *d, *_d;
> > > > struct dma_chan *chan = NULL;
> > > > + struct device_link *dl;
> > > >
> > > > if (is_of_node(fwnode))
> > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > #endif
> > > >
> > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > >
> > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > have device, consumer should link to chan's device, not dmaengine device
> > > because some dmaengine support per channel clock\power management.
> >
> > I get your point. Can you give me some pointers please? To me it seems
> > like the dma_chan_dev is only used for sysfs purpose according the
> > dmaengine.h.
>
> Not really, there are other dma engineer already reuse it for other purpose.
> So It needs update kernel doc for dma_chan_dev.
Okay.
> > > chan's device's parent devices is dmaengine devices. it should also work
> > > for sdma case
> >
> > I see, this must be tested of course.
> > > > if (chan->device->create_devlink) {
> > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> >
> > According device_link.rst: using DL_FLAG_STATELESS and
> > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> >
> > > if (pm_runtime_active(dev))
> > > flags |= DL_FLAG_RPM_ACTIVE;
> >
> > This is of course interessting, thanks for the hint.
> >
> > > When create device link (apply channel), consume may active.
> >
> > I have read it as: "resue the supplier and ensure that the supplier
> > follows the consumer runtime state".
> >
> > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> >
> > Huh.. you used the dmaengine device too?
>
> /**
> * struct dma_chan_dev - relate sysfs device node to backing channel device
> * @chan: driver channel device
> * @device: sysfs device
> * @dev_id: parent dma_device dev_id
> * @chan_dma_dev: The channel is using custom/different dma-mapping
> * compared to the parent dma_device
> */
> struct dma_chan_dev {
> struct dma_chan *chan;
> struct device device;
> int dev_id;
> bool chan_dma_dev;
> };
>
> struct dma_chan {
> struct dma_device *device; /// this one should be dmaengine
> struct dma_chan_dev *dev; /// this one is pre-chan device.
> }
Argh.. mixed it within my head while writing the mail :/
Regards,
Marco
On Wed, Sep 10, 2025 at 11:34:28AM +0200, Marco Felsch wrote:
> On 25-09-09, Frank Li wrote:
> > On Tue, Sep 09, 2025 at 02:03:09PM +0200, Marco Felsch wrote:
> > > Hi Frank,
> > >
> > > On 25-09-03, Frank Li wrote:
> > > > On Wed, Sep 03, 2025 at 03:06:17PM +0200, Marco Felsch wrote:
> > > > > Add support to create device_links between dmaengine suppliers and the
> > > > > dma consumers. This shifts the device dep-chain teardown/bringup logic
> > > > > to the driver core.
> > > > >
> > > > > Moving this to the core allows the dmaengine drivers to simplify the
> > > > > .remove() hooks and also to ensure that no dmaengine driver is ever
> > > > > removed before the consumer is removed.
> > > > >
> > > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > > > ---
> > > >
> > > > Thank you work for devlink between dmaengine and devices. I have similar
> > > > idea.
> > > >
> > > > This patch should be first patch.
> > >
> > > I can shuffle it of course!
> > >
> > > > The below what planned commit message in my local tree.
> > >
> > > Okay, so you focused on runtime PM handling. Not quite sure if I can
> > > test this feature with the SDMA engine. I also have limited time for
> > > this feature.
> > >
> > > Is it okay for you and the DMA maintainers to add the runtime PM feature
> > > as separate patch (provided by NXP/Frank)?
> >
> > we can support runtime pm later.
> >
> > >
> > > > Implementing runtime PM for DMA channels is challenging. If a channel
> > > > resumes at allocation and suspends at free, the DMA engine often remains on
> > > > because most drivers request a channel at probe.
> > > >
> > > > Tracking the number of pending DMA descriptors is also problematic, as some
> > > > consumers append new descriptors in atomic contexts, such as IRQ handlers,
> > > > where runtime resume cannot be called.
> > > >
> > > > Using a device link simplifies this issue. If a consumer requires data
> > > > transfer, it must be in a runtime-resumed state, ensuring that the DMA
> > > > channel is also active by device link. This allows safe operations, like
> > > > appending new descriptors. Conversely, when the consumer no longer requires
> > > > data transfer, both it and the supplier (DMA channel) can enter a suspended
> > > > state if no other consumer is using it.
> > > >
> > > > Introduce the `create_link` flag to enable this feature.
> > > >
> > > > also suggest add create_link flag to enable this feature in case some
> > > > side impact to other dma-engine. After some time test, we can enable it
> > > > default.
> > >
> > > What regressions do you have in mind? I wouldn't hide the feature behind
> > > a flag because this may slow done the convert process, because no one is
> > > interessted in, or has no time for testing, ...
> >
> > Unlike other devices, like phys, regulator, mailbox..., which auto create
> > devlink at probe. I am not clear why dma skip this one. So I think there
> > should be some reason behind. Maybe other people, rob or Vinod Koul know
> > the reason.
> >
> > static const struct supplier_bindings of_supplier_bindings[] = {
> > ...
> > { .parse_prop = parse_dmas, .optional = true, },
> >
> > If remove "optional = true", devlink will auto create. I am not sure why
> > set true here.
>
> I've seen this too. Could be because DMA controllers + users aren't OF
> related and therefore should be handled within the framework itself.
Not sure, may be some historical reason. I have not enough confidence just
because I don't know why optional = true here.
So I think you can post this patch seperated with good cover letter, may
someone jump into discussion.
Frank
>
> > > > > drivers/dma/dmaengine.c | 8 ++++++++
> > > > > 1 file changed, 8 insertions(+)
> > > > >
> > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > > > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..a50652bc70b8ce9d4edabfaa781b3432ee47d31e 100644
> > > > > --- a/drivers/dma/dmaengine.c
> > > > > +++ b/drivers/dma/dmaengine.c
> > > > > @@ -817,6 +817,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > struct dma_device *d, *_d;
> > > > > struct dma_chan *chan = NULL;
> > > > > + struct device_link *dl;
> > > > >
> > > > > if (is_of_node(fwnode))
> > > > > chan = of_dma_request_slave_channel(to_of_node(fwnode), name);
> > > > > @@ -858,6 +859,13 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> > > > > /* No functional issue if it fails, users are supposed to test before use */
> > > > > #endif
> > > > >
> > > > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > >
> > > > chan->device->dev is dmaengine devices. But some dmaengine's each channel
> > > > have device, consumer should link to chan's device, not dmaengine device
> > > > because some dmaengine support per channel clock\power management.
> > >
> > > I get your point. Can you give me some pointers please? To me it seems
> > > like the dma_chan_dev is only used for sysfs purpose according the
> > > dmaengine.h.
> >
> > Not really, there are other dma engineer already reuse it for other purpose.
> > So It needs update kernel doc for dma_chan_dev.
>
> Okay.
>
> > > > chan's device's parent devices is dmaengine devices. it should also work
> > > > for sdma case
> > >
> > > I see, this must be tested of course.
> > > > > if (chan->device->create_devlink) {
> > > > u32 flags = DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
> > >
> > > According device_link.rst: using DL_FLAG_STATELESS and
> > > DL_FLAG_AUTOREMOVE_CONSUMER is invalid.
> > >
> > > > if (pm_runtime_active(dev))
> > > > flags |= DL_FLAG_RPM_ACTIVE;
> > >
> > > This is of course interessting, thanks for the hint.
> > >
> > > > When create device link (apply channel), consume may active.
> > >
> > > I have read it as: "resue the supplier and ensure that the supplier
> > > follows the consumer runtime state".
> > >
> > > > dl = device_link_add(chan->slave, &chan->dev->device, flags);
> > >
> > > Huh.. you used the dmaengine device too?
> >
> > /**
> > * struct dma_chan_dev - relate sysfs device node to backing channel device
> > * @chan: driver channel device
> > * @device: sysfs device
> > * @dev_id: parent dma_device dev_id
> > * @chan_dma_dev: The channel is using custom/different dma-mapping
> > * compared to the parent dma_device
> > */
> > struct dma_chan_dev {
> > struct dma_chan *chan;
> > struct device device;
> > int dev_id;
> > bool chan_dma_dev;
> > };
> >
> > struct dma_chan {
> > struct dma_device *device; /// this one should be dmaengine
> > struct dma_chan_dev *dev; /// this one is pre-chan device.
> > }
>
> Argh.. mixed it within my head while writing the mail :/
>
> Regards,
> Marco
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