Annotating USB device Location in DT

Annotating USB device Location in DT

[Ricardo Ribalda]

Hi all,

I'm working on a way to annotate the location of a USB device within a
system, specifically whether it's "user-facing" or "world-facing."

There's precedent for this type of annotation:

- ACPI: Uses the '_PLD' property for this purpose
(https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#pld-physical-location-of-device).
We already leverage this for MIPI camera sensors
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/pci/intel/ipu-bridge.c#n265).

- Device Tree : Has a property for this within
video-interface-devices.yaml
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/media/video-interface-devices.yaml#n386).

I propose adding a similar property to usb-device.yaml
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/usb/usb-device.yaml).

The ultimate goal is to have this information consumed by the video
driver and exposed to userspace via the V4L2_CID_CAMERA_ORIENTATION
control (https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-camera.html).

What do you think about this?

Thanks,

-- 
Ricardo Ribalda

Re: Annotating USB device Location in DT

[Greg KH]

On Thu, Dec 12, 2024 at 02:42:34PM +0100, Ricardo Ribalda wrote:
> Hi all,
> 
> I'm working on a way to annotate the location of a USB device within a
> system, specifically whether it's "user-facing" or "world-facing."
> 
> There's precedent for this type of annotation:
> 
> - ACPI: Uses the '_PLD' property for this purpose
> (https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#pld-physical-location-of-device).
> We already leverage this for MIPI camera sensors
> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/pci/intel/ipu-bridge.c#n265).
> 
> - Device Tree : Has a property for this within
> video-interface-devices.yaml
> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/media/video-interface-devices.yaml#n386).
> 
> I propose adding a similar property to usb-device.yaml
> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/usb/usb-device.yaml).
> 
> The ultimate goal is to have this information consumed by the video
> driver and exposed to userspace via the V4L2_CID_CAMERA_ORIENTATION
> control (https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-camera.html).
> 
> What do you think about this?

I think you should copy what ACPI does here, as long as it doesn't
conflict with the existing video-interface-devices.yaml definition.
Will that work?

thanks,

greg k-h

Re: Annotating USB device Location in DT

[Alan Stern]

On Thu, Dec 12, 2024 at 03:03:51PM +0100, Greg KH wrote:
> On Thu, Dec 12, 2024 at 02:42:34PM +0100, Ricardo Ribalda wrote:
> > Hi all,
> > 
> > I'm working on a way to annotate the location of a USB device within a
> > system, specifically whether it's "user-facing" or "world-facing."
> > 
> > There's precedent for this type of annotation:
> > 
> > - ACPI: Uses the '_PLD' property for this purpose
> > (https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/06_Device_Configuration/Device_Configuration.html#pld-physical-location-of-device).
> > We already leverage this for MIPI camera sensors
> > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/pci/intel/ipu-bridge.c#n265).
> > 
> > - Device Tree : Has a property for this within
> > video-interface-devices.yaml
> > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/media/video-interface-devices.yaml#n386).
> > 
> > I propose adding a similar property to usb-device.yaml
> > (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/usb/usb-device.yaml).
> > 
> > The ultimate goal is to have this information consumed by the video
> > driver and exposed to userspace via the V4L2_CID_CAMERA_ORIENTATION
> > control (https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-camera.html).
> > 
> > What do you think about this?
> 
> I think you should copy what ACPI does here, as long as it doesn't
> conflict with the existing video-interface-devices.yaml definition.

Right.  While the notions of "user-facing" and "world-facing" might make 
sense for cameras, they do not make sense for arbitrary USB devices.  So 
they shouldn't be part of the general USB device description.

Alan Stern

> Will that work?
> 
> thanks,
> 
> greg k-h
>