linux-kernel - Re: [PATCH v2 12/12] media: uvcvideo: Do not create MC entities for virtual entities

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Message-ID: <20250629180534.GN24912@pendragon.ideasonboard.com>
Date: Sun, 29 Jun 2025 21:05:34 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 12/12] media: uvcvideo: Do not create MC entities for
 virtual entities

Hi Ricardo,

Thank you for the patch.

I would use "software entities" and not "virtual entities" in the
subject line and everywhere else, as those entities are not virtual.

On Thu, Jun 05, 2025 at 05:53:05PM +0000, Ricardo Ribalda wrote:
> Neither the GPIO nor the SWENTITY entities form part of the device
> pipeline. We just create them to hold emulated uvc controls.
> 
> When the device initializes, a warning is thrown by the v4l2 core:
> uvcvideo 1-1:1.0: Entity type for entity SWENTITY was not initialized!
> 
> There are no entity function that matches what we are doing here, and
> it does not make to much sense to create a function for entities that
> do not really exist.

I don't agree with this. The purpose of reporting entities to userspace
through the MC API is to let application enumerate what entities a
device contains. Being able to enumerate software entities seems as
useful as being able to enumerate hardware entities.

> Do not create MC entities for them and pretend nothing happened here.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_entity.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/media/usb/uvc/uvc_entity.c b/drivers/media/usb/uvc/uvc_entity.c
> index d1a652ef35ec34801bd39a5124b834edf838a79e..2dbeb4ab0c4c8cc763ff2dcd2d836a50f3c6a040 100644
> --- a/drivers/media/usb/uvc/uvc_entity.c
> +++ b/drivers/media/usb/uvc/uvc_entity.c
> @@ -72,6 +72,16 @@ static int uvc_mc_init_entity(struct uvc_video_chain *chain,
>  {
>  	int ret;
>  
> +	/*
> +	 * Do not initialize virtual entities, they do not really exist
> +	 * and are not connected to any other entities.
> +	 */
> +	switch (UVC_ENTITY_TYPE(entity)) {
> +	case UVC_EXT_GPIO_UNIT:
> +	case UVC_SWENTITY_UNIT:
> +		return 0;
> +	}
> +
>  	if (UVC_ENTITY_TYPE(entity) != UVC_TT_STREAMING) {
>  		u32 function;
>  

-- 
Regards,

Laurent Pinchart