When ACPI table includes _PLD fields for a device, create a new
directory (pld) in sysfs to share _PLD fields.

Currently without PLD information, when there are multiple of same
devices, it is hard to distinguish which device corresponds to which
physical device in which location. For example, when there are two Type
C connectors, it is hard to find out which connector corresponds to the
Type C port on the left panel versus the Type C port on the right panel.
With PLD information provided, we can determine which specific device at
which location is doing what.

Since PLD information is to be used for finding where physical device is
located in user's perspective, pld sysfs directory will only be created
for ACPI_BUS_TYPE_DEVICE with user_visible field set as 1.

Signed-off-by: Won Chung <wonchung@google.com>
---
Changes in v6:
- Add pld to acpi_device only if it is a user visible device.

Changes in v5:
- Store pld to acpi_device in acpi_store_pld_crc() and rename it as
  acpi_store_pld().

Changes in v4:
- Create seperate files for each _PLD fields instead of having a single
  file with all fields included.
- Create a new directory pld that contains _PLD fields

 Documentation/ABI/testing/sysfs-bus-acpi | 107 +++++++++++++++++++++++
 drivers/acpi/device_sysfs.c              |  51 +++++++++++
 drivers/acpi/scan.c                      |  12 ++-
 include/acpi/acpi_bus.h                  |   1 +
 4 files changed, 168 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-acpi b/Documentation/ABI/testing/sysfs-bus-acpi
index 58abacf59b2a..b8b71c8f3cfd 100644
--- a/Documentation/ABI/testing/sysfs-bus-acpi
+++ b/Documentation/ABI/testing/sysfs-bus-acpi
@@ -96,3 +96,110 @@ Description:
 		hardware, if the _HRV control method is present.  It is mostly
 		useful for non-PCI devices because lspci can list the hardware
 		version for PCI devices.
+
+What:		/sys/bus/acpi/devices/.../pld/
+Date:		Feb, 2022
+Contact:	Won Chung <wonchung@google.com>
+Description:
+		This directory contains the output of the device object's _PLD
+		control method, if present. This information provides details
+		on physical location of a device.
+
+What:		/sys/bus/acpi/devices/.../pld/revision
+Date:		Feb, 2022
+Contact:	Won Chung <wonchung@google.com>
+Description:
+		The current revision is 0x2.
+
+What:           /sys/bus/acpi/devices/.../pld/group_token
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Unique numerical value identifying a group.
+
+What:           /sys/bus/acpi/devices/.../pld/group_position
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Identifies this device connection point’s position in the group.
+
+What:           /sys/bus/acpi/devices/.../pld/user_visible
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Set if the device connection point can be seen by the user
+		without disassembly.
+
+What:           /sys/bus/acpi/devices/.../pld/dock
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Set if the device connection point resides in a docking station
+		or port replicator.
+
+What:           /sys/bus/acpi/devices/.../pld/bay
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Set if describing a device in a bay or if device connection
+		point is a bay.
+
+What:           /sys/bus/acpi/devices/.../pld/lid
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Set if this device connection point resides on the lid of
+		laptop system.
+
+What:           /sys/bus/acpi/devices/.../pld/panel
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Describes which panel surface of the system’s housing the
+		device connection point resides on:
+		0 - Top
+		1 - Bottom
+		2 - Left
+		3 - Right
+		4 - Front
+		5 - Back
+		6 - Unknown (Vertical Position and Horizontal Position will be
+		ignored)
+
+What:           /sys/bus/acpi/devices/.../pld/vertical_position
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		0 - Upper
+		1 - Center
+		2 - Lower
+
+What:           /sys/bus/acpi/devices/.../pld/horizontal_position
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		ACPI specification does not define horizontal position field.
+		Can be used as either
+		0 - Left
+		1 - Center
+		2 - Right
+		or
+		0 - Leftmost
+		and higher numbers going toward the right.
+
+What:           /sys/bus/acpi/devices/.../pld/shape
+Date:           Feb, 2022
+Contact:        Won Chung <wonchung@google.com>
+Description:
+		Describes the shape of the device connection point.
+		0 - Round
+		1 - Oval
+		2 - Square
+		3 - Vertical Rectangle
+		4 - Horizontal Rectangle
+		5 - Vertical Trapezoid
+		6 - Horizontal Trapezoid
+		7 - Unknown - Shape rendered as a Rectangle with dotted lines
+		8 - Chamfered
+		15:9 - Reserved
+
diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
index d5d6403ba07b..2702f78a2503 100644
--- a/drivers/acpi/device_sysfs.c
+++ b/drivers/acpi/device_sysfs.c
@@ -509,6 +509,49 @@ static ssize_t status_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(status);
 
+#define DEV_ATTR_PLD_PROP(prop) \
+	static ssize_t prop##_show(struct device *dev, struct device_attribute *attr, \
+		char *buf) \
+{ \
+	struct acpi_device *acpi_dev = to_acpi_device(dev); \
+	if (acpi_dev->pld == NULL) \
+		return -EIO; \
+	return sprintf(buf, "%u\n", acpi_dev->pld->prop); \
+}; \
+static DEVICE_ATTR_RO(prop)
+
+DEV_ATTR_PLD_PROP(revision);
+DEV_ATTR_PLD_PROP(group_token);
+DEV_ATTR_PLD_PROP(group_position);
+DEV_ATTR_PLD_PROP(user_visible);
+DEV_ATTR_PLD_PROP(dock);
+DEV_ATTR_PLD_PROP(bay);
+DEV_ATTR_PLD_PROP(lid);
+DEV_ATTR_PLD_PROP(panel);
+DEV_ATTR_PLD_PROP(vertical_position);
+DEV_ATTR_PLD_PROP(horizontal_position);
+DEV_ATTR_PLD_PROP(shape);
+
+static struct attribute *dev_attr_pld[] = {
+	&dev_attr_revision.attr,
+	&dev_attr_group_token.attr,
+	&dev_attr_group_position.attr,
+	&dev_attr_user_visible.attr,
+	&dev_attr_dock.attr,
+	&dev_attr_bay.attr,
+	&dev_attr_lid.attr,
+	&dev_attr_panel.attr,
+	&dev_attr_vertical_position.attr,
+	&dev_attr_horizontal_position.attr,
+	&dev_attr_shape.attr,
+	NULL,
+};
+
+static struct attribute_group dev_attr_pld_group = {
+	.name = "pld",
+	.attrs = dev_attr_pld,
+};
+
 /**
  * acpi_device_setup_files - Create sysfs attributes of an ACPI device.
  * @dev: ACPI device object.
@@ -595,6 +638,12 @@ int acpi_device_setup_files(struct acpi_device *dev)
 						    &dev_attr_real_power_state);
 	}
 
+	if (acpi_has_method(dev->handle, "_PLD") && dev->pld != NULL) {
+		result = device_add_group(&dev->dev, &dev_attr_pld_group);
+		if (result)
+			goto end;
+	}
+
 	acpi_expose_nondev_subnodes(&dev->dev.kobj, &dev->data);
 
 end:
@@ -645,4 +694,6 @@ void acpi_device_remove_files(struct acpi_device *dev)
 		device_remove_file(&dev->dev, &dev_attr_status);
 	if (dev->handle)
 		device_remove_file(&dev->dev, &dev_attr_path);
+	if (acpi_has_method(dev->handle, "_PLD") && dev->pld != NULL)
+		device_remove_group(&dev->dev, &dev_attr_pld_group);
 }
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 1331756d4cfc..35ac7bcc05ed 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -668,7 +668,7 @@ static int acpi_tie_acpi_dev(struct acpi_device *adev)
 	return 0;
 }
 
-static void acpi_store_pld_crc(struct acpi_device *adev)
+static void acpi_store_pld(struct acpi_device *adev)
 {
 	struct acpi_pld_info *pld;
 	acpi_status status;
@@ -678,7 +678,13 @@ static void acpi_store_pld_crc(struct acpi_device *adev)
 		return;
 
 	adev->pld_crc = crc32(~0, pld, sizeof(*pld));
-	ACPI_FREE(pld);
+
+	if (adev->device_type == ACPI_BUS_TYPE_DEVICE && pld->user_visible) {
+		adev->pld = pld;
+	} else {
+		adev->pld = NULL;
+		ACPI_FREE(pld);
+	}
 }
 
 static int __acpi_device_add(struct acpi_device *device,
@@ -739,7 +745,7 @@ static int __acpi_device_add(struct acpi_device *device,
 	if (device->wakeup.flags.valid)
 		list_add_tail(&device->wakeup_list, &acpi_wakeup_device_list);
 
-	acpi_store_pld_crc(device);
+	acpi_store_pld(device);
 
 	mutex_unlock(&acpi_device_lock);
 
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index ca88c4706f2b..929e726a666b 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -381,6 +381,7 @@ struct acpi_device {
 	struct acpi_hotplug_context *hp;
 	struct acpi_driver *driver;
 	const struct acpi_gpio_mapping *driver_gpios;
+	struct acpi_pld_info *pld;
 	void *driver_data;
 	struct device dev;
 	unsigned int physical_node_count;
-- 
2.35.1.265.g69c8d7142f-goog

On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
>
> When ACPI table includes _PLD fields for a device, create a new
> directory (pld) in sysfs to share _PLD fields.

This version of the patch loos better to me, but I'm not sure if it
goes into the right direction overall.

> Currently without PLD information, when there are multiple of same
> devices, it is hard to distinguish which device corresponds to which
> physical device in which location. For example, when there are two Type
> C connectors, it is hard to find out which connector corresponds to the
> Type C port on the left panel versus the Type C port on the right panel.

So I think that this is your primary use case and I'm wondering if
this is the best way to address it.

Namely, by exposing _PLD information under the ACPI device object,
you'll make user space wanting to use that information depend on this
interface, but the problem is not ACPI-specific (inevitably, it will
appear on systems using DT, sooner or later) and making the user space
interface related to it depend on ACPI doesn't look like a perfect
choice.

IOW, why don't you create a proper ABI for this in the Type C
subsystem and expose the information needed by user space in a generic
way that can be based on the _PLD information on systems with ACPI?

On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> >
> > When ACPI table includes _PLD fields for a device, create a new
> > directory (pld) in sysfs to share _PLD fields.
>
> This version of the patch loos better to me, but I'm not sure if it
> goes into the right direction overall.
>
> > Currently without PLD information, when there are multiple of same
> > devices, it is hard to distinguish which device corresponds to which
> > physical device in which location. For example, when there are two Type
> > C connectors, it is hard to find out which connector corresponds to the
> > Type C port on the left panel versus the Type C port on the right panel.
>
> So I think that this is your primary use case and I'm wondering if
> this is the best way to address it.
>
> Namely, by exposing _PLD information under the ACPI device object,
> you'll make user space wanting to use that information depend on this
> interface, but the problem is not ACPI-specific (inevitably, it will
> appear on systems using DT, sooner or later) and making the user space
> interface related to it depend on ACPI doesn't look like a perfect
> choice.
>
> IOW, why don't you create a proper ABI for this in the Type C
> subsystem and expose the information needed by user space in a generic
> way that can be based on the _PLD information on systems with ACPI?

Hi Rafael,

Thank you for the review.

I was thinking that _PLD info is specific to ACPI since it is part of
the ACPI table. Could you explain a little bit more on why you think
exposing _PLD fields is not an ACPI-specific problem?

I gave an example of how _PLD fields can be used for specifying Type C
connectors, but it is not Type C specific. For Chrome OS, we plan to
initially add PLD to not only Type C connectors but also USB port
devices (including Type C and Type A). Also, PLD can be used in the
future for describing other types of ports too like HDMI. (Benson and
Prashant, please correct or add if I am wrong or missing some
information) Maybe my commit message was not detailed enough..

I am also curious what Heikki thinks about this. Heikki, can you take
a look and share your thoughts?

Thank you,
Won

On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
>
> On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > >
> > > When ACPI table includes _PLD fields for a device, create a new
> > > directory (pld) in sysfs to share _PLD fields.
> >
> > This version of the patch loos better to me, but I'm not sure if it
> > goes into the right direction overall.
> >
> > > Currently without PLD information, when there are multiple of same
> > > devices, it is hard to distinguish which device corresponds to which
> > > physical device in which location. For example, when there are two Type
> > > C connectors, it is hard to find out which connector corresponds to the
> > > Type C port on the left panel versus the Type C port on the right panel.
> >
> > So I think that this is your primary use case and I'm wondering if
> > this is the best way to address it.
> >
> > Namely, by exposing _PLD information under the ACPI device object,
> > you'll make user space wanting to use that information depend on this
> > interface, but the problem is not ACPI-specific (inevitably, it will
> > appear on systems using DT, sooner or later) and making the user space
> > interface related to it depend on ACPI doesn't look like a perfect
> > choice.
> >
> > IOW, why don't you create a proper ABI for this in the Type C
> > subsystem and expose the information needed by user space in a generic
> > way that can be based on the _PLD information on systems with ACPI?
>
> Hi Rafael,
>
> Thank you for the review.
>
> I was thinking that _PLD info is specific to ACPI since it is part of
> the ACPI table. Could you explain a little bit more on why you think
> exposing _PLD fields is not an ACPI-specific problem?

Hi Rafael again,

Sorry for the silly question here. I misunderstood your comment a bit,
but I talked to Benson and Prashant for clarification. I understand
now what you mean by it is not an ACPI-specific problem and exposing
PLD would depend on ACPI.

>
> I gave an example of how _PLD fields can be used for specifying Type C
> connectors, but it is not Type C specific. For Chrome OS, we plan to
> initially add PLD to not only Type C connectors but also USB port
> devices (including Type C and Type A). Also, PLD can be used in the
> future for describing other types of ports too like HDMI. (Benson and
> Prashant, please correct or add if I am wrong or missing some
> information) Maybe my commit message was not detailed enough..
>
> I am also curious what Heikki thinks about this. Heikki, can you take
> a look and share your thoughts?

I am still curious what you and Heikki think about this since it may
not be a Type C specific issue. We can start from adding generic
location info to Type C subsystem first, as you suggested, then
consider how to do the same for USB devices and Type A ports
afterwards. I would appreciate sharing any thoughts or feedback. Thank
you very much!

Won

>
> Thank you,
> Won

On Mon, Feb 14, 2022 at 02:58:44PM -0800, Won Chung wrote:
> On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
> >
> > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > > >
> > > > When ACPI table includes _PLD fields for a device, create a new
> > > > directory (pld) in sysfs to share _PLD fields.
> > >
> > > This version of the patch loos better to me, but I'm not sure if it
> > > goes into the right direction overall.
> > >
> > > > Currently without PLD information, when there are multiple of same
> > > > devices, it is hard to distinguish which device corresponds to which
> > > > physical device in which location. For example, when there are two Type
> > > > C connectors, it is hard to find out which connector corresponds to the
> > > > Type C port on the left panel versus the Type C port on the right panel.
> > >
> > > So I think that this is your primary use case and I'm wondering if
> > > this is the best way to address it.
> > >
> > > Namely, by exposing _PLD information under the ACPI device object,
> > > you'll make user space wanting to use that information depend on this
> > > interface, but the problem is not ACPI-specific (inevitably, it will
> > > appear on systems using DT, sooner or later) and making the user space
> > > interface related to it depend on ACPI doesn't look like a perfect
> > > choice.
> > >
> > > IOW, why don't you create a proper ABI for this in the Type C
> > > subsystem and expose the information needed by user space in a generic
> > > way that can be based on the _PLD information on systems with ACPI?
> >
> > Hi Rafael,
> >
> > Thank you for the review.
> >
> > I was thinking that _PLD info is specific to ACPI since it is part of
> > the ACPI table. Could you explain a little bit more on why you think
> > exposing _PLD fields is not an ACPI-specific problem?
> 
> Hi Rafael again,
> 
> Sorry for the silly question here. I misunderstood your comment a bit,
> but I talked to Benson and Prashant for clarification. I understand
> now what you mean by it is not an ACPI-specific problem and exposing
> PLD would depend on ACPI.
> 
> >
> > I gave an example of how _PLD fields can be used for specifying Type C
> > connectors, but it is not Type C specific. For Chrome OS, we plan to
> > initially add PLD to not only Type C connectors but also USB port
> > devices (including Type C and Type A). Also, PLD can be used in the
> > future for describing other types of ports too like HDMI. (Benson and
> > Prashant, please correct or add if I am wrong or missing some
> > information) Maybe my commit message was not detailed enough..
> >
> > I am also curious what Heikki thinks about this. Heikki, can you take
> > a look and share your thoughts?
> 
> I am still curious what you and Heikki think about this since it may
> not be a Type C specific issue. We can start from adding generic
> location info to Type C subsystem first, as you suggested, then
> consider how to do the same for USB devices and Type A ports
> afterwards. I would appreciate sharing any thoughts or feedback. Thank
> you very much!

Like you said, _PLD is not Type-C specific. We can't limit it to any
specific device class. For example, I'm pretty ssure that sooner or
later we want to get this information in user space also with camera
sensors, and probable with a few other things as well.

I think the question here is, can we create a some kind of an
abstraction layer for the user space that exposes the device location
details in generic Linux specific way - so with ACPI it would utilise
the _PLD, and with DT something else (today AFAIK DT does not have
any way to describe locations of the devices). Maybe I'm wrong?

But if that is the question, then IMO the answer is: maybe one day,
but not today, and even if we one day can come up with something like
that, we still should expose the _PLD as ACPI specific information to
the user space as is.

Even if one day we have common sysfs attributes for all the devices
that contain the location of the device in some form, those attributes
will almost certainly have only a sub-set of the _PLD details, a
sub-set that works also with DT.
IMO the user space should always have access to all the necessary _PLD
details in their raw form if needed, even if those common device
location attributes exist - duplicated information or not. And debugfs
unfortunately is also not OK for that, because the user space needs to
be able to also rely on access to the additional details if needed.

We can limit the _PLD fields that we expose to the ones that we know
we need today (and probable should limit them to those), and we can of
course have a Kconfig option for the _PLD sysfs information if we want
to, but let's not start this by trying to figure out what kind of
abstraction we want for this. Right now we simply can not do that.

thanks,

-- 
heikki

On Tue, Feb 15, 2022 at 11:14 AM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> On Mon, Feb 14, 2022 at 02:58:44PM -0800, Won Chung wrote:
> > On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
> > >
> > > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > > >
> > > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > > > >
> > > > > When ACPI table includes _PLD fields for a device, create a new
> > > > > directory (pld) in sysfs to share _PLD fields.
> > > >
> > > > This version of the patch loos better to me, but I'm not sure if it
> > > > goes into the right direction overall.
> > > >
> > > > > Currently without PLD information, when there are multiple of same
> > > > > devices, it is hard to distinguish which device corresponds to which
> > > > > physical device in which location. For example, when there are two Type
> > > > > C connectors, it is hard to find out which connector corresponds to the
> > > > > Type C port on the left panel versus the Type C port on the right panel.
> > > >
> > > > So I think that this is your primary use case and I'm wondering if
> > > > this is the best way to address it.
> > > >
> > > > Namely, by exposing _PLD information under the ACPI device object,
> > > > you'll make user space wanting to use that information depend on this
> > > > interface, but the problem is not ACPI-specific (inevitably, it will
> > > > appear on systems using DT, sooner or later) and making the user space
> > > > interface related to it depend on ACPI doesn't look like a perfect
> > > > choice.
> > > >
> > > > IOW, why don't you create a proper ABI for this in the Type C
> > > > subsystem and expose the information needed by user space in a generic
> > > > way that can be based on the _PLD information on systems with ACPI?
> > >
> > > Hi Rafael,
> > >
> > > Thank you for the review.
> > >
> > > I was thinking that _PLD info is specific to ACPI since it is part of
> > > the ACPI table. Could you explain a little bit more on why you think
> > > exposing _PLD fields is not an ACPI-specific problem?
> >
> > Hi Rafael again,
> >
> > Sorry for the silly question here. I misunderstood your comment a bit,
> > but I talked to Benson and Prashant for clarification. I understand
> > now what you mean by it is not an ACPI-specific problem and exposing
> > PLD would depend on ACPI.
> >
> > >
> > > I gave an example of how _PLD fields can be used for specifying Type C
> > > connectors, but it is not Type C specific. For Chrome OS, we plan to
> > > initially add PLD to not only Type C connectors but also USB port
> > > devices (including Type C and Type A). Also, PLD can be used in the
> > > future for describing other types of ports too like HDMI. (Benson and
> > > Prashant, please correct or add if I am wrong or missing some
> > > information) Maybe my commit message was not detailed enough..
> > >
> > > I am also curious what Heikki thinks about this. Heikki, can you take
> > > a look and share your thoughts?
> >
> > I am still curious what you and Heikki think about this since it may
> > not be a Type C specific issue. We can start from adding generic
> > location info to Type C subsystem first, as you suggested, then
> > consider how to do the same for USB devices and Type A ports
> > afterwards. I would appreciate sharing any thoughts or feedback. Thank
> > you very much!
>
> Like you said, _PLD is not Type-C specific. We can't limit it to any
> specific device class. For example, I'm pretty sure that sooner or
> later we want to get this information in user space also with camera
> sensors, and probable with a few other things as well.
>
> I think the question here is, can we create a some kind of an
> abstraction layer for the user space that exposes the device location
> details in generic Linux specific way - so with ACPI it would utilise
> the _PLD, and with DT something else (today AFAIK DT does not have
> any way to describe locations of the devices). Maybe I'm wrong?

No, you aren't.

> But if that is the question, then IMO the answer is: maybe one day,
> but not today,

Why not?

> and even if we one day can come up with something like
> that, we still should expose the _PLD as ACPI specific information to
> the user space as is.

Why would it need that information in this particular format?

> Even if one day we have common sysfs attributes for all the devices
> that contain the location of the device in some form, those attributes
> will almost certainly have only a sub-set of the _PLD details, a
> sub-set that works also with DT.

That doesn't have to be the case.

However, things linke cpuidle have been invented to provide user space
interfaces for features that previously were only available on systems
with ACPI.  Why is _PLD different?

> IMO the user space should always have access to all the necessary _PLD
> details in their raw form if needed, even if those common device
> location attributes exist - duplicated information or not.

Again, why would it need that information?

> And debugfs
> unfortunately is also not OK for that, because the user space needs to
> be able to also rely on access to the additional details if needed.

What additional details do you mean?

> We can limit the _PLD fields that we expose to the ones that we know
> we need today (and probable should limit them to those), and we can of
> course have a Kconfig option for the _PLD sysfs information if we want
> to, but let's not start this by trying to figure out what kind of
> abstraction we want for this. Right now we simply can not do that.

Why can't we?

Adding Greg, who should be involved in this discussion IMO.

On Mon, Feb 14, 2022 at 11:59 PM Won Chung <wonchung@google.com> wrote:
>
> On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
> >
> > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > > >
> > > > When ACPI table includes _PLD fields for a device, create a new
> > > > directory (pld) in sysfs to share _PLD fields.
> > >
> > > This version of the patch loos better to me, but I'm not sure if it
> > > goes into the right direction overall.
> > >
> > > > Currently without PLD information, when there are multiple of same
> > > > devices, it is hard to distinguish which device corresponds to which
> > > > physical device in which location. For example, when there are two Type
> > > > C connectors, it is hard to find out which connector corresponds to the
> > > > Type C port on the left panel versus the Type C port on the right panel.
> > >
> > > So I think that this is your primary use case and I'm wondering if
> > > this is the best way to address it.
> > >
> > > Namely, by exposing _PLD information under the ACPI device object,
> > > you'll make user space wanting to use that information depend on this
> > > interface, but the problem is not ACPI-specific (inevitably, it will
> > > appear on systems using DT, sooner or later) and making the user space
> > > interface related to it depend on ACPI doesn't look like a perfect
> > > choice.
> > >
> > > IOW, why don't you create a proper ABI for this in the Type C
> > > subsystem and expose the information needed by user space in a generic
> > > way that can be based on the _PLD information on systems with ACPI?
> >
> > Hi Rafael,
> >
> > Thank you for the review.
> >
> > I was thinking that _PLD info is specific to ACPI since it is part of
> > the ACPI table. Could you explain a little bit more on why you think
> > exposing _PLD fields is not an ACPI-specific problem?

_PLD is an interface defined by ACPI, but its purpose is not ACPI-specific.

> Hi Rafael again,
>
> Sorry for the silly question here. I misunderstood your comment a bit,
> but I talked to Benson and Prashant for clarification. I understand
> now what you mean by it is not an ACPI-specific problem and exposing
> PLD would depend on ACPI.

Right.

> >
> > I gave an example of how _PLD fields can be used for specifying Type C
> > connectors, but it is not Type C specific. For Chrome OS, we plan to
> > initially add PLD to not only Type C connectors but also USB port
> > devices (including Type C and Type A). Also, PLD can be used in the
> > future for describing other types of ports too like HDMI. (Benson and
> > Prashant, please correct or add if I am wrong or missing some
> > information) Maybe my commit message was not detailed enough..
> >
> > I am also curious what Heikki thinks about this. Heikki, can you take
> > a look and share your thoughts?
>
> I am still curious what you and Heikki think about this since it may
> not be a Type C specific issue. We can start from adding generic
> location info to Type C subsystem first, as you suggested, then
> consider how to do the same for USB devices and Type A ports
> afterwards. I would appreciate sharing any thoughts or feedback. Thank
> you very much!

I don't really think that this is a Type C problem either.

It has existed for a long time in the USB world, for example, or
wherever there are user-accessible ports, but it looks like in the
Type C case it has become vitally important.

My point is that writing user space depending on accessing _PLD
information exposed under an ACPI device interface that only
corresponds to the device in question and in the ACPI-specific format
would be a mistake (Greg, please let me know if you disagree).  That's
because (a) it would depend on ACPI tables being present (so it
wouldn't work on systems without them) and (b) it would depend on the
format of data which covers information that isn't likely to be
relevant.

If this information is exposed by the kernel verbatim and user space
depending on this information is created, it will not be possible to
unexpose it even if it turns out that exposing it has been a mistake.

OTOH, if only the relevant pieces of information are exposed in a
generic way, it is always possible to expose more pieces of it in the
future as needed.

On Tue, Feb 15, 2022 at 3:04 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> Adding Greg, who should be involved in this discussion IMO.
>
> On Mon, Feb 14, 2022 at 11:59 PM Won Chung <wonchung@google.com> wrote:
> >
> > On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
> > >
> > > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > > >
> > > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > > > >
> > > > > When ACPI table includes _PLD fields for a device, create a new
> > > > > directory (pld) in sysfs to share _PLD fields.
> > > >
> > > > This version of the patch loos better to me, but I'm not sure if it
> > > > goes into the right direction overall.
> > > >
> > > > > Currently without PLD information, when there are multiple of same
> > > > > devices, it is hard to distinguish which device corresponds to which
> > > > > physical device in which location. For example, when there are two Type
> > > > > C connectors, it is hard to find out which connector corresponds to the
> > > > > Type C port on the left panel versus the Type C port on the right panel.
> > > >
> > > > So I think that this is your primary use case and I'm wondering if
> > > > this is the best way to address it.
> > > >
> > > > Namely, by exposing _PLD information under the ACPI device object,
> > > > you'll make user space wanting to use that information depend on this
> > > > interface, but the problem is not ACPI-specific (inevitably, it will
> > > > appear on systems using DT, sooner or later) and making the user space
> > > > interface related to it depend on ACPI doesn't look like a perfect
> > > > choice.
> > > >
> > > > IOW, why don't you create a proper ABI for this in the Type C
> > > > subsystem and expose the information needed by user space in a generic
> > > > way that can be based on the _PLD information on systems with ACPI?
> > >
> > > Hi Rafael,
> > >
> > > Thank you for the review.
> > >
> > > I was thinking that _PLD info is specific to ACPI since it is part of
> > > the ACPI table. Could you explain a little bit more on why you think
> > > exposing _PLD fields is not an ACPI-specific problem?
>
> _PLD is an interface defined by ACPI, but its purpose is not ACPI-specific.
>
> > Hi Rafael again,
> >
> > Sorry for the silly question here. I misunderstood your comment a bit,
> > but I talked to Benson and Prashant for clarification. I understand
> > now what you mean by it is not an ACPI-specific problem and exposing
> > PLD would depend on ACPI.
>
> Right.
>
> > >
> > > I gave an example of how _PLD fields can be used for specifying Type C
> > > connectors, but it is not Type C specific. For Chrome OS, we plan to
> > > initially add PLD to not only Type C connectors but also USB port
> > > devices (including Type C and Type A). Also, PLD can be used in the
> > > future for describing other types of ports too like HDMI. (Benson and
> > > Prashant, please correct or add if I am wrong or missing some
> > > information) Maybe my commit message was not detailed enough..
> > >
> > > I am also curious what Heikki thinks about this. Heikki, can you take
> > > a look and share your thoughts?
> >
> > I am still curious what you and Heikki think about this since it may
> > not be a Type C specific issue. We can start from adding generic
> > location info to Type C subsystem first, as you suggested, then
> > consider how to do the same for USB devices and Type A ports
> > afterwards. I would appreciate sharing any thoughts or feedback. Thank
> > you very much!
>
> I don't really think that this is a Type C problem either.
>
> It has existed for a long time in the USB world, for example, or
> wherever there are user-accessible ports, but it looks like in the
> Type C case it has become vitally important.
>
> My point is that writing user space depending on accessing _PLD
> information exposed under an ACPI device interface that only
> corresponds to the device in question and in the ACPI-specific format
> would be a mistake (Greg, please let me know if you disagree).  That's
> because (a) it would depend on ACPI tables being present (so it
> wouldn't work on systems without them) and (b) it would depend on the
> format of data which covers information that isn't likely to be
> relevant.

Also finding _PLD information for a given "real" device would not be
particularly straightforward as it would involve looking up an ACPI
device interface corresponding to it in the first place and then
retrieving the _PLD data from it.

On Tue, Feb 15, 2022 at 03:04:54PM +0100, Rafael J. Wysocki wrote:
> Adding Greg, who should be involved in this discussion IMO.
> 
> On Mon, Feb 14, 2022 at 11:59 PM Won Chung <wonchung@google.com> wrote:
> >
> > On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
> > >
> > > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > > >
> > > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.com> wrote:
> > > > >
> > > > > When ACPI table includes _PLD fields for a device, create a new
> > > > > directory (pld) in sysfs to share _PLD fields.
> > > >
> > > > This version of the patch loos better to me, but I'm not sure if it
> > > > goes into the right direction overall.
> > > >
> > > > > Currently without PLD information, when there are multiple of same
> > > > > devices, it is hard to distinguish which device corresponds to which
> > > > > physical device in which location. For example, when there are two Type
> > > > > C connectors, it is hard to find out which connector corresponds to the
> > > > > Type C port on the left panel versus the Type C port on the right panel.
> > > >
> > > > So I think that this is your primary use case and I'm wondering if
> > > > this is the best way to address it.
> > > >
> > > > Namely, by exposing _PLD information under the ACPI device object,
> > > > you'll make user space wanting to use that information depend on this
> > > > interface, but the problem is not ACPI-specific (inevitably, it will
> > > > appear on systems using DT, sooner or later) and making the user space
> > > > interface related to it depend on ACPI doesn't look like a perfect
> > > > choice.
> > > >
> > > > IOW, why don't you create a proper ABI for this in the Type C
> > > > subsystem and expose the information needed by user space in a generic
> > > > way that can be based on the _PLD information on systems with ACPI?
> > >
> > > Hi Rafael,
> > >
> > > Thank you for the review.
> > >
> > > I was thinking that _PLD info is specific to ACPI since it is part of
> > > the ACPI table. Could you explain a little bit more on why you think
> > > exposing _PLD fields is not an ACPI-specific problem?
> 
> _PLD is an interface defined by ACPI, but its purpose is not ACPI-specific.
> 
> > Hi Rafael again,
> >
> > Sorry for the silly question here. I misunderstood your comment a bit,
> > but I talked to Benson and Prashant for clarification. I understand
> > now what you mean by it is not an ACPI-specific problem and exposing
> > PLD would depend on ACPI.
> 
> Right.
> 
> > >
> > > I gave an example of how _PLD fields can be used for specifying Type C
> > > connectors, but it is not Type C specific. For Chrome OS, we plan to
> > > initially add PLD to not only Type C connectors but also USB port
> > > devices (including Type C and Type A). Also, PLD can be used in the
> > > future for describing other types of ports too like HDMI. (Benson and
> > > Prashant, please correct or add if I am wrong or missing some
> > > information) Maybe my commit message was not detailed enough..
> > >
> > > I am also curious what Heikki thinks about this. Heikki, can you take
> > > a look and share your thoughts?
> >
> > I am still curious what you and Heikki think about this since it may
> > not be a Type C specific issue. We can start from adding generic
> > location info to Type C subsystem first, as you suggested, then
> > consider how to do the same for USB devices and Type A ports
> > afterwards. I would appreciate sharing any thoughts or feedback. Thank
> > you very much!
> 
> I don't really think that this is a Type C problem either.
> 
> It has existed for a long time in the USB world, for example, or
> wherever there are user-accessible ports, but it looks like in the
> Type C case it has become vitally important.
> 
> My point is that writing user space depending on accessing _PLD
> information exposed under an ACPI device interface that only
> corresponds to the device in question and in the ACPI-specific format
> would be a mistake (Greg, please let me know if you disagree).  That's
> because (a) it would depend on ACPI tables being present (so it
> wouldn't work on systems without them) and (b) it would depend on the
> format of data which covers information that isn't likely to be
> relevant.
> 
> If this information is exposed by the kernel verbatim and user space
> depending on this information is created, it will not be possible to
> unexpose it even if it turns out that exposing it has been a mistake.
> 
> OTOH, if only the relevant pieces of information are exposed in a
> generic way, it is always possible to expose more pieces of it in the
> future as needed.

There are pending patches on the linux-usb mailing list from Heikki to
help expand on the typec information in sysfs in a generic way.  Won,
please work with the linux-usb developers on this change and do not do
anything that is ACPI-specific and only.  That way will not be good for
anyone involved.

Please see:
	https://lore.kernel.org/r/20220203144657.16527-1-heikki.krogerus@linux.intel.com

for the current discussion.

thanks,

greg k-h