linux-kernel - Re: [PATCH v2 08/12] media: uvcvideo: Add support for V4L2_CID_CAMERA

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Message-ID: <71d9aa58-e166-419b-9d32-839f5c4ad62c@redhat.com>
Date: Mon, 14 Jul 2025 16:36:42 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.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>
Cc: 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 08/12] media: uvcvideo: Add support for
 V4L2_CID_CAMERA_ORIENTATION

Hi,

On 5-Jun-25 19:53, Ricardo Ribalda wrote:
> Fetch the orientation from the fwnode and map it into a control.
> 
> The uvc driver does not use the media controller, so we need to create a
> virtual entity, like we previously did with the external gpio.
> 
> We do not re-purpose the external gpio entity because its is planned to
> remove it.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

...

Taking a second look at this I noticed the following:

> @@ -1869,11 +1869,15 @@ static int uvc_scan_device(struct uvc_device *dev)
>  		return -1;
>  	}
>  
> -	/* Add GPIO entity to the first chain. */
> -	if (dev->gpio_unit) {
> +	/* Add virtual entities to the first chain. */
> +	if (dev->gpio_unit || dev->swentity_unit) {
>  		chain = list_first_entry(&dev->chains,
>  					 struct uvc_video_chain, list);
> -		list_add_tail(&dev->gpio_unit->chain, &chain->entities);
> +		if (dev->gpio_unit)
> +			list_add_tail(&dev->gpio_unit->chain, &chain->entities);
> +		if (dev->swentity_unit)
> +			list_add_tail(&dev->swentity_unit->chain,
> +				      &chain->entities);
>  	}
>  
>  	return 0;

The double checking of if (dev->gpio_unit) / if (dev->swentity_unit) looks
unnecessary here list_first_entry() is pretty cheap and this only runs
once at probe() time. So maybe:

	/* Add virtual entities to the first chain. */
	chain = list_first_entry(&dev->chains, struct uvc_video_chain, list);

	if (dev->gpio_unit)
		list_add_tail(&dev->gpio_unit->chain, &chain->entities);

	if (dev->swentity_unit)
		list_add_tail(&dev->swentity_unit->chain, &chain->entities);

?

...

Regards,

Hans