linux-kernel - Re: [PATCH v4 5/5] media: uvcvideo: Use prio state from v4l2

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Message-ID: <843b32df-64d5-4711-8415-4044174e575f@kernel.org>
Date: Mon, 16 Jun 2025 22:50:54 +0200
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Hans de Goede <hdegoede@...hat.com>, Hans Verkuil <hans@...erkuil.nl>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/5] media: uvcvideo: Use prio state from v4l2_device

Hi Ricardo,

On 16-Jun-25 8:30 PM, Ricardo Ribalda wrote:
> Hello All
> 
> On Mon, 16 Jun 2025 at 17:24, Ricardo Ribalda <ribalda@...omium.org> wrote:
>>
>> Currently, a UVC device can have multiple chains, and each chain maintains
>> its own priority state. While this behavior is technically correct for UVC,
>> uvcvideo is the *only* V4L2 driver that does not utilize the priority state
>> defined within `v4l2_device`.
>>
>> This patch modifies uvcvideo to use the `v4l2_device` priority state. While
>> this might not be strictly "correct" for uvcvideo's multi-chain design, it
>> aligns uvcvideo with the rest of the V4L2 drivers, providing "correct enough"
>> behavior and enabling code cleanup in v4l2-core. Also, multi-chain
>> devices are extremely rare, they are typically implemented as two
>> independent usb devices.
> 
> As the cover letter says, this last patch 5/5 is a RFC. We can decide
> if it is worth to keep it or not.
> 
> The pros is that we can do some cleanup in the core, the cons is that
> it might break kAPI.

I've no objections against this change, but lets wait and see what
Laurent has to say.

Regards,

Hans




>> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
>> ---
>>  drivers/media/usb/uvc/uvc_driver.c | 2 --
>>  drivers/media/usb/uvc/uvcvideo.h   | 1 -
>>  2 files changed, 3 deletions(-)
>>
>> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
>> index accfb4ca3c72cb899185ddc8ecf4e29143d58fc6..e3795e40f14dc325e5bd120f5f45b60937841641 100644
>> --- a/drivers/media/usb/uvc/uvc_driver.c
>> +++ b/drivers/media/usb/uvc/uvc_driver.c
>> @@ -1728,7 +1728,6 @@ static struct uvc_video_chain *uvc_alloc_chain(struct uvc_device *dev)
>>         INIT_LIST_HEAD(&chain->entities);
>>         mutex_init(&chain->ctrl_mutex);
>>         chain->dev = dev;
>> -       v4l2_prio_init(&chain->prio);
>>
>>         return chain;
>>  }
>> @@ -2008,7 +2007,6 @@ int uvc_register_video_device(struct uvc_device *dev,
>>         vdev->fops = fops;
>>         vdev->ioctl_ops = ioctl_ops;
>>         vdev->release = uvc_release;
>> -       vdev->prio = &stream->chain->prio;
>>         vdev->queue = &queue->queue;
>>         vdev->lock = &queue->mutex;
>>         if (type == V4L2_BUF_TYPE_VIDEO_OUTPUT)
>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
>> index 3e6d2d912f3a1cfcf63b2bc8edd3f86f3da305db..5ed9785d59c698cc7e0ac69955b892f932961617 100644
>> --- a/drivers/media/usb/uvc/uvcvideo.h
>> +++ b/drivers/media/usb/uvc/uvcvideo.h
>> @@ -354,7 +354,6 @@ struct uvc_video_chain {
>>                                                  * uvc_fh.pending_async_ctrls
>>                                                  */
>>
>> -       struct v4l2_prio_state prio;            /* V4L2 priority state */
>>         u32 caps;                               /* V4L2 chain-wide caps */
>>         u8 ctrl_class_bitmap;                   /* Bitmap of valid classes */
>>  };
>>
>> --
>> 2.50.0.rc1.591.g9c95f17f64-goog
>>
> 
>