[libcamera-devel] [PATCH] libcamera: pipeline: uvcvideo: Infer camera location from removable attribute

[paul.elder at ideasonboard.com]

Hi Laurent,

On Thu, May 26, 2022 at 04:30:25PM +0300, Laurent Pinchart via libcamera-devel wrote:
> Use the removable attribute exposed by the USB device in sysfs to infer
> if the camera is an external (when removable) or front (when
> non-removable) camera. This is likely not perfect as the removable
> attribute is derived from ACPI data which may not always be accurate,
> and non-ACPI platforms likely report all devices as removable. Still,
> this is a first step upon which a better method could be built.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>

> ---
>  src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 33 +++++++++++++++++---
>  1 file changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> index 2ebf2788c3b4..53b2f23ab029 100644
> --- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> +++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> @@ -501,13 +501,36 @@ int UVCCameraData::init(MediaDevice *media)
>  
>  	video_->bufferReady.connect(this, &UVCCameraData::bufferReady);
>  
> -	/*
> -	 * \todo Find a way to tell internal and external UVC cameras apart.
> -	 * Until then, treat all UVC cameras as external.
> -	 */
> -	properties_.set(properties::Location, properties::CameraLocationExternal);
>  	properties_.set(properties::Model, utils::toAscii(media->model()));
>  
> +	/*
> +	 * Derive the location from the device removable attribute in sysfs.
> +	 * Non-removable devices are assumed to be front as we lack detailed
> +	 * location information, and removable device are considered external.
> +	 *
> +	 * The sysfs removable attribute is derived from the ACPI _UPC attribute
> +	 * if available, or from the USB hub descriptors otherwise. ACPI data
> +	 * may not be very reliable, and the USB hub descriptors may not be
> +	 * accurate on DT-based platforms. A heuristic may need to be
> +	 * implemented later if too many devices end up being miscategorized.
> +	 *
> +	 * \todo Find a way to tell front and back devices apart. This could
> +	 * come from the ACPI _PLD, but that may be even more unreliable than
> +	 * the _UPC.
> +	 */
> +	properties::LocationEnum location = properties::CameraLocationExternal;
> +	std::ifstream file(video_->devicePath() + "/../removable");
> +	if (file.is_open()) {
> +		std::string value;
> +		std::getline(file, value);
> +		file.close();
> +
> +		if (value == "fixed")
> +			location = properties::CameraLocationFront;
> +	}
> +
> +	properties_.set(properties::Location, location);
> +
>  	/*
>  	 * Get the current format in order to initialize the sensor array
>  	 * properties.
> 
> base-commit: f8e4649680303ce9b7dace5ad1344fcb450013ac
> prerequisite-patch-id: edbf31ed9d7f5374e17b34936fe1aa8dea2eac44