This will add usb_alloc_noncoherent() and usb_free_noncoherent()
functions to support alloc and free buffer in a dma-noncoherent way.
To explicit manage the memory ownership for the kernel and device,
this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
and call it at proper time. The management requires the user save
sg_table returned by usb_alloc_noncoherent() to urb->sgt.
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
Changes in v4:
- improve if-else logic
Changes in v3:
- put Return section at the end of description
- correct some abbreviations
- remove usb_dma_noncoherent_sync_for_cpu() and
usb_dma_noncoherent_sync_for_device()
- do DMA sync in usb_hcd_map_urb_for_dma() and
usb_hcd_unmap_urb_for_dma()
- call flush_kernel_vmap_range() for OUT transfers
and invalidate_kernel_vmap_range() for IN transfers
---
drivers/usb/core/hcd.c | 33 ++++++++++++-----
drivers/usb/core/usb.c | 80 ++++++++++++++++++++++++++++++++++++++++++
include/linux/usb.h | 11 ++++++
3 files changed, 116 insertions(+), 8 deletions(-)
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index c22de97432a0..42d9d8db0968 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1342,29 +1342,35 @@ void usb_hcd_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
if (IS_ENABLED(CONFIG_HAS_DMA) &&
- (urb->transfer_flags & URB_DMA_MAP_SG))
+ (urb->transfer_flags & URB_DMA_MAP_SG)) {
dma_unmap_sg(hcd->self.sysdev,
urb->sg,
urb->num_sgs,
dir);
- else if (IS_ENABLED(CONFIG_HAS_DMA) &&
- (urb->transfer_flags & URB_DMA_MAP_PAGE))
+ } else if (IS_ENABLED(CONFIG_HAS_DMA) &&
+ (urb->transfer_flags & URB_DMA_MAP_PAGE)) {
dma_unmap_page(hcd->self.sysdev,
urb->transfer_dma,
urb->transfer_buffer_length,
dir);
- else if (IS_ENABLED(CONFIG_HAS_DMA) &&
- (urb->transfer_flags & URB_DMA_MAP_SINGLE))
+ } else if (IS_ENABLED(CONFIG_HAS_DMA) &&
+ (urb->transfer_flags & URB_DMA_MAP_SINGLE)) {
dma_unmap_single(hcd->self.sysdev,
urb->transfer_dma,
urb->transfer_buffer_length,
dir);
- else if (urb->transfer_flags & URB_MAP_LOCAL)
+ } else if (urb->transfer_flags & URB_MAP_LOCAL) {
hcd_free_coherent(urb->dev->bus,
&urb->transfer_dma,
&urb->transfer_buffer,
urb->transfer_buffer_length,
dir);
+ } else if ((urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP) && urb->sgt) {
+ dma_sync_sgtable_for_cpu(hcd->self.sysdev, urb->sgt, dir);
+ if (dir == DMA_FROM_DEVICE)
+ invalidate_kernel_vmap_range(urb->transfer_buffer,
+ urb->transfer_buffer_length);
+ }
/* Make it safe to call this routine more than once */
urb->transfer_flags &= ~(URB_DMA_MAP_SG | URB_DMA_MAP_PAGE |
@@ -1425,8 +1431,10 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
}
dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
- if (urb->transfer_buffer_length != 0
- && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
+ if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
+ if (!urb->transfer_buffer_length)
+ return ret;
+
if (hcd->localmem_pool) {
ret = hcd_alloc_coherent(
urb->dev->bus, mem_flags,
@@ -1491,7 +1499,16 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
if (ret && (urb->transfer_flags & (URB_SETUP_MAP_SINGLE |
URB_SETUP_MAP_LOCAL)))
usb_hcd_unmap_urb_for_dma(hcd, urb);
+ } else {
+ if (!urb->sgt)
+ return ret;
+
+ if (dir == DMA_TO_DEVICE)
+ flush_kernel_vmap_range(urb->transfer_buffer,
+ urb->transfer_buffer_length);
+ dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
}
+
return ret;
}
EXPORT_SYMBOL_GPL(usb_hcd_map_urb_for_dma);
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 118fa4c93a79..fca7735fc660 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -1030,6 +1030,86 @@ void usb_free_coherent(struct usb_device *dev, size_t size, void *addr,
}
EXPORT_SYMBOL_GPL(usb_free_coherent);
+/**
+ * usb_alloc_noncoherent - allocate dma-noncoherent buffer for URB_NO_xxx_DMA_MAP
+ * @dev: device the buffer will be used with
+ * @size: requested buffer size
+ * @mem_flags: affect whether allocation may block
+ * @dma: used to return DMA address of buffer
+ * @dir: DMA transfer direction
+ * @table: used to return sg_table of allocated memory
+ *
+ * To explicit manage the memory ownership for the kernel vs the device by
+ * USB core, the user needs save sg_table to urb->sgt. Then USB core will
+ * do DMA sync for CPU and device properly.
+ *
+ * When the buffer is no longer used, free it with usb_free_noncoherent().
+ *
+ * Return: Either null (indicating no buffer could be allocated), or the
+ * cpu-space pointer to a buffer that may be used to perform DMA to the
+ * specified device. Such cpu-space buffers are returned along with the DMA
+ * address (through the pointer provided).
+ */
+void *usb_alloc_noncoherent(struct usb_device *dev, size_t size,
+ gfp_t mem_flags, dma_addr_t *dma,
+ enum dma_data_direction dir,
+ struct sg_table **table)
+{
+ struct device *dmadev;
+ struct sg_table *sgt;
+ void *buffer;
+
+ if (!dev || !dev->bus)
+ return NULL;
+
+ dmadev = bus_to_hcd(dev->bus)->self.sysdev;
+
+ sgt = dma_alloc_noncontiguous(dmadev, size, dir, mem_flags, 0);
+ if (!sgt)
+ return NULL;
+
+ buffer = dma_vmap_noncontiguous(dmadev, size, sgt);
+ if (!buffer) {
+ dma_free_noncontiguous(dmadev, size, sgt, dir);
+ return NULL;
+ }
+
+ *table = sgt;
+ *dma = sg_dma_address(sgt->sgl);
+
+ return buffer;
+}
+EXPORT_SYMBOL_GPL(usb_alloc_noncoherent);
+
+/**
+ * usb_free_noncoherent - free memory allocated with usb_alloc_noncoherent()
+ * @dev: device the buffer was used with
+ * @size: requested buffer size
+ * @addr: CPU address of buffer
+ * @dir: DMA transfer direction
+ * @table: describe the allocated and DMA mapped memory,
+ *
+ * This reclaims an I/O buffer, letting it be reused. The memory must have
+ * been allocated using usb_alloc_noncoherent(), and the parameters must match
+ * those provided in that allocation request.
+ */
+void usb_free_noncoherent(struct usb_device *dev, size_t size,
+ void *addr, enum dma_data_direction dir,
+ struct sg_table *table)
+{
+ struct device *dmadev;
+
+ if (!dev || !dev->bus)
+ return;
+ if (!addr)
+ return;
+
+ dmadev = bus_to_hcd(dev->bus)->self.sysdev;
+ dma_vunmap_noncontiguous(dmadev, addr);
+ dma_free_noncontiguous(dmadev, size, table, dir);
+}
+EXPORT_SYMBOL_GPL(usb_free_noncoherent);
+
/*
* Notifications of device and interface registration
*/
diff --git a/include/linux/usb.h b/include/linux/usb.h
index e8662843e68c..9ade441ab4c8 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1619,6 +1619,7 @@ struct urb {
void *transfer_buffer; /* (in) associated data buffer */
dma_addr_t transfer_dma; /* (in) dma addr for transfer_buffer */
struct scatterlist *sg; /* (in) scatter gather buffer list */
+ struct sg_table *sgt; /* (in) scatter gather table for noncoherent buffer */
int num_mapped_sgs; /* (internal) mapped sg entries */
int num_sgs; /* (in) number of entries in the sg list */
u32 transfer_buffer_length; /* (in) data buffer length */
@@ -1824,6 +1825,16 @@ void *usb_alloc_coherent(struct usb_device *dev, size_t size,
void usb_free_coherent(struct usb_device *dev, size_t size,
void *addr, dma_addr_t dma);
+enum dma_data_direction;
+
+void *usb_alloc_noncoherent(struct usb_device *dev, size_t size,
+ gfp_t mem_flags, dma_addr_t *dma,
+ enum dma_data_direction dir,
+ struct sg_table **table);
+void usb_free_noncoherent(struct usb_device *dev, size_t size,
+ void *addr, enum dma_data_direction dir,
+ struct sg_table *table);
+
/*-------------------------------------------------------------------*
* SYNCHRONOUS CALL SUPPORT *
*-------------------------------------------------------------------*/
--
2.34.1On Thu, Jul 03, 2025 at 06:38:09PM +0800, Xu Yang wrote:
> This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> functions to support alloc and free buffer in a dma-noncoherent way.
>
> To explicit manage the memory ownership for the kernel and device,
> this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> and call it at proper time. The management requires the user save
> sg_table returned by usb_alloc_noncoherent() to urb->sgt.
>
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
>
> ---
> Changes in v4:
> - improve if-else logic
>
> Changes in v3:
> - put Return section at the end of description
> - correct some abbreviations
> - remove usb_dma_noncoherent_sync_for_cpu() and
> usb_dma_noncoherent_sync_for_device()
> - do DMA sync in usb_hcd_map_urb_for_dma() and
> usb_hcd_unmap_urb_for_dma()
> - call flush_kernel_vmap_range() for OUT transfers
> and invalidate_kernel_vmap_range() for IN transfers
> ---
> drivers/usb/core/hcd.c | 33 ++++++++++++-----
> drivers/usb/core/usb.c | 80 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/usb.h | 11 ++++++
> 3 files changed, 116 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index c22de97432a0..42d9d8db0968 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1425,8 +1431,10 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> }
>
> dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> - if (urb->transfer_buffer_length != 0
> - && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> + if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> + if (!urb->transfer_buffer_length)
> + return ret;
> +
> if (hcd->localmem_pool) {
> ret = hcd_alloc_coherent(
> urb->dev->bus, mem_flags,
> @@ -1491,7 +1499,16 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> if (ret && (urb->transfer_flags & (URB_SETUP_MAP_SINGLE |
> URB_SETUP_MAP_LOCAL)))
> usb_hcd_unmap_urb_for_dma(hcd, urb);
> + } else {
> + if (!urb->sgt)
> + return ret;
> +
> + if (dir == DMA_TO_DEVICE)
> + flush_kernel_vmap_range(urb->transfer_buffer,
> + urb->transfer_buffer_length);
> + dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
> }
This could be done a little more cleanly. It's always awkward to read
an "else" clause for a negated test.
Instead, change the "else" to:
if (urb->transfer_flags & URB_NO_TRANFER_DMA_MAP) {
and move this whole section to the top of the big "if". Then you can
change the test that's already there to:
} else if (urb->transfer_buffer_length != 0) {
Alan Stern
On Thu, Jul 03, 2025 at 10:35:23AM -0400, Alan Stern wrote:
> On Thu, Jul 03, 2025 at 06:38:09PM +0800, Xu Yang wrote:
> > This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> > functions to support alloc and free buffer in a dma-noncoherent way.
> >
> > To explicit manage the memory ownership for the kernel and device,
> > this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> > and call it at proper time. The management requires the user save
> > sg_table returned by usb_alloc_noncoherent() to urb->sgt.
> >
> > Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> >
> > ---
> > Changes in v4:
> > - improve if-else logic
> >
> > Changes in v3:
> > - put Return section at the end of description
> > - correct some abbreviations
> > - remove usb_dma_noncoherent_sync_for_cpu() and
> > usb_dma_noncoherent_sync_for_device()
> > - do DMA sync in usb_hcd_map_urb_for_dma() and
> > usb_hcd_unmap_urb_for_dma()
> > - call flush_kernel_vmap_range() for OUT transfers
> > and invalidate_kernel_vmap_range() for IN transfers
> > ---
> > drivers/usb/core/hcd.c | 33 ++++++++++++-----
> > drivers/usb/core/usb.c | 80 ++++++++++++++++++++++++++++++++++++++++++
> > include/linux/usb.h | 11 ++++++
> > 3 files changed, 116 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > index c22de97432a0..42d9d8db0968 100644
> > --- a/drivers/usb/core/hcd.c
> > +++ b/drivers/usb/core/hcd.c
>
> > @@ -1425,8 +1431,10 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > }
> >
> > dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> > - if (urb->transfer_buffer_length != 0
> > - && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> > + if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> > + if (!urb->transfer_buffer_length)
> > + return ret;
> > +
> > if (hcd->localmem_pool) {
> > ret = hcd_alloc_coherent(
> > urb->dev->bus, mem_flags,
> > @@ -1491,7 +1499,16 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > if (ret && (urb->transfer_flags & (URB_SETUP_MAP_SINGLE |
> > URB_SETUP_MAP_LOCAL)))
> > usb_hcd_unmap_urb_for_dma(hcd, urb);
> > + } else {
> > + if (!urb->sgt)
> > + return ret;
> > +
> > + if (dir == DMA_TO_DEVICE)
> > + flush_kernel_vmap_range(urb->transfer_buffer,
> > + urb->transfer_buffer_length);
> > + dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
> > }
>
> This could be done a little more cleanly. It's always awkward to read
> an "else" clause for a negated test.
Agree.
>
> Instead, change the "else" to:
>
> if (urb->transfer_flags & URB_NO_TRANFER_DMA_MAP) {
>
> and move this whole section to the top of the big "if". Then you can
> change the test that's already there to:
>
> } else if (urb->transfer_buffer_length != 0) {
Okay. It's a better choice.
Thanks,
Xu Yang
>
> Alan Stern
On Thu, Jul 03, 2025 at 06:38:09PM +0800, Xu Yang wrote:
> This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> functions to support alloc and free buffer in a dma-noncoherent way.
>
> To explicit manage the memory ownership for the kernel and device,
> this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> and call it at proper time. The management requires the user save
> sg_table returned by usb_alloc_noncoherent() to urb->sgt.
...
> dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> - if (urb->transfer_buffer_length != 0
> - && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> + if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> + if (!urb->transfer_buffer_length)
> + return ret;
This return ret out of a sudden are quite fragile. Please, move to use return 0
directly where it is supposed to be 0.
...
> + } else {
> + if (!urb->sgt)
> + return ret;
Ditto.
> + if (dir == DMA_TO_DEVICE)
> + flush_kernel_vmap_range(urb->transfer_buffer,
> + urb->transfer_buffer_length);
> + dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
> }
> return ret;
Ditto?
--
With Best Regards,
Andy Shevchenko
On Thu, Jul 03, 2025 at 04:46:57PM +0300, Andy Shevchenko wrote:
> On Thu, Jul 03, 2025 at 06:38:09PM +0800, Xu Yang wrote:
> > This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> > functions to support alloc and free buffer in a dma-noncoherent way.
> >
> > To explicit manage the memory ownership for the kernel and device,
> > this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> > and call it at proper time. The management requires the user save
> > sg_table returned by usb_alloc_noncoherent() to urb->sgt.
>
> ...
>
> > dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> > - if (urb->transfer_buffer_length != 0
> > - && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> > + if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> > + if (!urb->transfer_buffer_length)
> > + return ret;
>
> This return ret out of a sudden are quite fragile. Please, move to use return 0
> directly where it is supposed to be 0.
Okay.
>
> ...
>
> > + } else {
> > + if (!urb->sgt)
> > + return ret;
>
> Ditto.
Okay.
>
> > + if (dir == DMA_TO_DEVICE)
> > + flush_kernel_vmap_range(urb->transfer_buffer,
> > + urb->transfer_buffer_length);
> > + dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
> > }
>
> > return ret;
>
> Ditto?
With Alan's suggestion, this patch will not touch this line.
Thanks,
Xu Yang
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
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