linux-kernel - Re: [PATCH v3 3/9] media: subdev: Add checks for subdev features

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Date: Thu, 11 Apr 2024 09:18:15 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Umang Jain <umang.jain@...asonboard.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil
 <hverkuil@...all.nl>, Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v3 3/9] media: subdev: Add checks for subdev features

On 11/04/2024 08:34, Umang Jain wrote:
> Hi Tomi,
> 
> On 10/04/24 6:05 pm, Tomi Valkeinen wrote:
>> Add some checks to verify that the subdev driver implements required
>> features.
>>
>> A subdevice that supports streams (V4L2_SUBDEV_FL_STREAMS) must do one
>> of the following:
>>
>> - Implement neither .enable/disable_streams() nor .s_stream(), if the
>>    subdev is part of a video driver that uses an internal method to
>>    enable the subdev.
>> - Implement only .enable/disable_streams(), if support for legacy
>>    sink-side subdevices is not needed.
>> - Implement .enable/disable_streams() and .s_stream(), if support for
>>    legacy sink-side subdevices is needed.
>>
>> At the moment the framework doesn't check this requirement. Add the
>> check.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> 
> The code looks aligned with the restrictions mentioned in the commit 
> message.
> 
> Only one question in case 3), does the .s_stream() needs to be helper 
> function I think, can we (or do we) need to check that as well?

Do you mean if in case 3, the s_stream should always be set to 
v4l2_subdev_s_stream_helper()?

I don't think so. The helper only works for subdevices with a single 
source pad. And even if the helper worked for multiple source pads, I 
don't see any specific reason to prevent the drivers from having their 
own implementation.

  Tomi

> Reviewed-by: Umang Jain <umang.jain@...asonboard.com>
> 
>> ---
>>   drivers/media/v4l2-core/v4l2-subdev.c | 27 +++++++++++++++++++++++++++
>>   1 file changed, 27 insertions(+)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c 
>> b/drivers/media/v4l2-core/v4l2-subdev.c
>> index 4a531c2b16c4..606a909cd778 100644
>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
>> @@ -1533,6 +1533,33 @@ int __v4l2_subdev_init_finalize(struct 
>> v4l2_subdev *sd, const char *name,
>>                   struct lock_class_key *key)
>>   {
>>       struct v4l2_subdev_state *state;
>> +    struct device *dev = sd->dev;
>> +    bool has_disable_streams;
>> +    bool has_enable_streams;
>> +    bool has_s_stream;
>> +
>> +    /* Check that the subdevice implements the required features */
>> +
>> +    has_s_stream = v4l2_subdev_has_op(sd, video, s_stream);
>> +    has_enable_streams = v4l2_subdev_has_op(sd, pad, enable_streams);
>> +    has_disable_streams = v4l2_subdev_has_op(sd, pad, disable_streams);
>> +
>> +    if (has_enable_streams != has_disable_streams) {
>> +        dev_err(dev,
>> +            "subdev '%s' must implement both or neither of 
>> .enable_streams() and .disable_streams()\n",
>> +            sd->name);
>> +        return -EINVAL;
>> +    }
>> +
>> +    if (sd->flags & V4L2_SUBDEV_FL_STREAMS) {
>> +        if (has_s_stream && !has_enable_streams) {
>> +            dev_err(dev,
>> +                "subdev '%s' must implement 
>> .enable/disable_streams()\n",
>> +                sd->name);
>> +
>> +            return -EINVAL;
>> +        }
>> +    }
>>       state = __v4l2_subdev_state_alloc(sd, name, key);
>>       if (IS_ERR(state))
>>
>