linux-kernel - Re: [PATCH v2 4/9] media: subdev: Fix use of sd->enabled_streams in call_s

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Date: Wed, 10 Apr 2024 13:52:04 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Hans Verkuil <hverkuil@...all.nl>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Umang Jain <umang.jain@...asonboard.com>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/9] media: subdev: Fix use of sd->enabled_streams in
 call_s_stream()

On 10/04/2024 13:05, Sakari Ailus wrote:
> Moi,
> 
> On Fri, Apr 05, 2024 at 12:14:22PM +0300, 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().
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.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 a15a41576918..94483b238f2a 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))
> 
> A single ! is enough on both sides.

Or perhaps (sd->streaming_enabled == !!enable).

> 
>>   		return 0;
>>   
>>   	if (enable)
>> @@ -442,7 +438,7 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
>>   	}
>>   
>>   	if (!ret)
>> -		sd->enabled_streams = enable ? BIT(0) : 0;
>> +		sd->streaming_enabled = !!enable;
> 
> No need for !! unless you think it needs to be very loud. Casting a
> non-boolean value to boolean results in true if it's non-zero.

Indeed. My coding style for booleans seems to be from times long past.

  Tomi

> 
>>   
>>   	return ret;
>>   }
>> 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;
>>   };
>>   
>>   
>>
>