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Message-ID: <e9f0ed24-6e24-4575-8028-b62eac1f37c6@ideasonboard.com>
Date: Thu, 11 Apr 2024 09:19:02 +0300
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Subject: Re: [PATCH v3 4/9] media: subdev: Fix use of sd->enabled_streams in
 call_s_stream()
To: Umang Jain <umang.jain@ideasonboard.com>
Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
 Mauro Carvalho Chehab <mchehab@kernel.org>, Hans Verkuil
 <hverkuil@xs4all.nl>, Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
 Sakari Ailus <sakari.ailus@linux.intel.com>
References: <20240410-enable-streams-impro-v3-0-e5e7a5da7420@ideasonboard.com>
 <20240410-enable-streams-impro-v3-4-e5e7a5da7420@ideasonboard.com>
 <a808c81c-2006-410e-ba8c-74c5405acbdf@ideasonboard.com>
From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
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In-Reply-To: <a808c81c-2006-410e-ba8c-74c5405acbdf@ideasonboard.com>
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On 11/04/2024 08:16, Umang Jain wrote:
> Hi Tomi,
> 
> Thank you for the patch
> 
> On 10/04/24 6:05 pm, Tomi Valkeinen wrote:
>> call_s_stream() uses sd->enabled_streams to track whether streaming has
>> already been enabled. However,
>> v4l2_subdev_enable/disable_streams_fallback(), which was the original
>> user of this field, already uses it, and
>> v4l2_subdev_enable/disable_streams_fallback() will call call_s_stream().
>>
>> This leads to a conflict as both functions set the field. Afaics, both
>> functions set the field to the same value, so it won't cause a runtime
>> bug, but it's still wrong and if we, e.g., change how
>> v4l2_subdev_enable/disable_streams_fallback() operates we might easily
>> cause bugs.
>>
>> Fix this by adding a new field, 'streaming_enabled', for
>> call_s_stream().
> 
> Just a suggestion, as this is only used in call_s_stream(), maybe naming 
> this field 's_stream_enabled' ?

Yes, I think that's a good idea.

  Tomi

> Rest looks good to me,
> 
> Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
> 
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>> ---
>>   drivers/media/v4l2-core/v4l2-subdev.c | 8 ++------
>>   include/media/v4l2-subdev.h           | 3 +++
>>   2 files changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c 
>> b/drivers/media/v4l2-core/v4l2-subdev.c
>> index 606a909cd778..6cd353d83dfc 100644
>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
>> @@ -421,12 +421,8 @@ static int call_s_stream(struct v4l2_subdev *sd, 
>> int enable)
>>        * The .s_stream() operation must never be called to start or 
>> stop an
>>        * already started or stopped subdev. Catch offenders but don't 
>> return
>>        * an error yet to avoid regressions.
>> -     *
>> -     * As .s_stream() is mutually exclusive with the 
>> .enable_streams() and
>> -     * .disable_streams() operation, we can use the enabled_streams 
>> field
>> -     * to store the subdev streaming state.
>>        */
>> -    if (WARN_ON(!!sd->enabled_streams == !!enable))
>> +    if (WARN_ON(sd->streaming_enabled == !!enable))
>>           return 0;
>>       ret = sd->ops->video->s_stream(sd, enable);
>> @@ -437,7 +433,7 @@ static int call_s_stream(struct v4l2_subdev *sd, 
>> int enable)
>>       }
>>       if (!ret) {
>> -        sd->enabled_streams = enable ? BIT(0) : 0;
>> +        sd->streaming_enabled = enable;
>>           if (enable)
>>               v4l2_subdev_enable_privacy_led(sd);
>> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
>> index a9e6b8146279..f55d03e0acc1 100644
>> --- a/include/media/v4l2-subdev.h
>> +++ b/include/media/v4l2-subdev.h
>> @@ -1043,6 +1043,8 @@ struct v4l2_subdev_platform_data {
>>    *             v4l2_subdev_enable_streams() and
>>    *             v4l2_subdev_disable_streams() helper functions for 
>> fallback
>>    *             cases.
>> + * @streaming_enabled: Tracks whether streaming has been enabled with 
>> s_stream.
>> + *                     This is only for call_s_stream() internal use.
>>    *
>>    * Each instance of a subdev driver should create this struct, either
>>    * stand-alone or embedded in a larger struct.
>> @@ -1091,6 +1093,7 @@ struct v4l2_subdev {
>>        */
>>       struct v4l2_subdev_state *active_state;
>>       u64 enabled_streams;
>> +    bool streaming_enabled;
>>   };
>>
>