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Message-ID: <a5ea5844-a7ba-408b-8007-2000dc94be24@ideasonboard.com>
Date: Thu, 4 Apr 2024 15:38:45 +0300
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Subject: Re: [PATCH 3/4] media: subdev: Improve
 v4l2_subdev_enable/disable_streams_fallback
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
 Hans Verkuil <hverkuil@xs4all.nl>,
 Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
 Umang Jain <umang.jain@ideasonboard.com>, linux-media@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240404-enable-streams-impro-v1-0-1017a35bbe07@ideasonboard.com>
 <20240404-enable-streams-impro-v1-3-1017a35bbe07@ideasonboard.com>
 <Zg6anfpQt80gSKjN@kekkonen.localdomain>
From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
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On 04/04/2024 15:18, Sakari Ailus wrote:
> Moi,
> 
> Thanks for the patch.
> 
> On Thu, Apr 04, 2024 at 01:50:02PM +0300, Tomi Valkeinen wrote:
>> v4l2_subdev_enable/disable_streams_fallback() supports falling back to
>> .s_stream() for subdevs with a single source pad. It also tracks the
>> enabled streams for that one pad in the sd->enabled_streams field.
>>
>> Tracking the enabled streams with sd->enabled_streams does not make
>> sense, as with .s_stream() there can only be a single stream per pad.
>> Thus, as the v4l2_subdev_enable/disable_streams_fallback() only supports
>> a single source pad, all we really need is a boolean which tells whether
>> streaming has been enabled on this pad or not.
>>
>> However, as we only need a true/false state for a pad (instead of
>> tracking which streams have been enabled for a pad), we can easily
>> extend the fallback mechanism to support multiple source pads as we only
>> need to keep track of which pads have been enabled.
>>
>> Change the sd->enabled_streams field to sd->enabled_pads, which is a
>> 64-bit bitmask tracking the enabled source pads. With this change we can
>> remove the restriction that
>> v4l2_subdev_enable/disable_streams_fallback() only supports a single
>> soruce pad.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>> ---
>>   drivers/media/v4l2-core/v4l2-subdev.c | 68 ++++++++++++++++++++---------------
>>   include/media/v4l2-subdev.h           |  9 +++--
>>   2 files changed, 44 insertions(+), 33 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
>> index 3b3310bce5d4..91298bb84e6b 100644
>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
>> @@ -2090,37 +2090,43 @@ static int v4l2_subdev_enable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
>>   					       u64 streams_mask)
>>   {
>>   	struct device *dev = sd->entity.graph_obj.mdev->dev;
>> -	unsigned int i;
>>   	int ret;
>>   
>>   	/*
>>   	 * The subdev doesn't implement pad-based stream enable, fall back
>> -	 * on the .s_stream() operation. This can only be done for subdevs that
>> -	 * have a single source pad, as sd->enabled_streams is global to the
>> -	 * subdev.
>> +	 * on the .s_stream() operation.
>>   	 */
>>   	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
>>   		return -EOPNOTSUPP;
>>   
>> -	for (i = 0; i < sd->entity.num_pads; ++i) {
>> -		if (i != pad && sd->entity.pads[i].flags & MEDIA_PAD_FL_SOURCE)
>> -			return -EOPNOTSUPP;
>> -	}
>> +	/*
>> +	 * .s_stream() means there is no streams support, so only allowed stream
>> +	 * is the imlicit stream 0.
>> +	 */
>> +	if (streams_mask != BIT_ULL(0))
>> +		return -EOPNOTSUPP;
>> +
>> +	/*
>> +	 * We use a 64-bit bitmask for tracking enabled pads, so only subdevices
>> +	 * with 64 pads or less can be supported.
>> +	 */
>> +	if (pad >= sizeof(sd->enabled_pads) * 8)
> 
> s/8/BITS_PER_BYTE/
> 
>> +		return -EOPNOTSUPP;
>>   
>> -	if (sd->enabled_streams & streams_mask) {
>> -		dev_dbg(dev, "set of streams %#llx already enabled on %s:%u\n",
>> -			streams_mask, sd->entity.name, pad);
>> +	if (sd->enabled_pads & BIT_ULL(pad)) {
>> +		dev_dbg(dev, "pad %u already enabled on %s\n",
>> +			pad, sd->entity.name);
>>   		return -EALREADY;
>>   	}
>>   
>> -	/* Start streaming when the first streams are enabled. */
>> -	if (!sd->enabled_streams) {
>> +	/* Start streaming when the first pad is enabled. */
>> +	if (!sd->enabled_pads) {
>>   		ret = v4l2_subdev_call(sd, video, s_stream, 1);
>>   		if (ret)
>>   			return ret;
>>   	}
>>   
>> -	sd->enabled_streams |= streams_mask;
>> +	sd->enabled_pads |= BIT_ULL(pad);
>>   
>>   	return 0;
>>   }
>> @@ -2207,37 +2213,43 @@ static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
>>   						u64 streams_mask)
>>   {
>>   	struct device *dev = sd->entity.graph_obj.mdev->dev;
>> -	unsigned int i;
>>   	int ret;
>>   
>>   	/*
>> -	 * If the subdev doesn't implement pad-based stream enable, fall  back
>> -	 * on the .s_stream() operation. This can only be done for subdevs that
>> -	 * have a single source pad, as sd->enabled_streams is global to the
>> -	 * subdev.
>> +	 * If the subdev doesn't implement pad-based stream enable, fall back
>> +	 * on the .s_stream() operation.
>>   	 */
>>   	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
>>   		return -EOPNOTSUPP;
>>   
>> -	for (i = 0; i < sd->entity.num_pads; ++i) {
>> -		if (i != pad && sd->entity.pads[i].flags & MEDIA_PAD_FL_SOURCE)
>> -			return -EOPNOTSUPP;
>> -	}
>> +	/*
>> +	 * .s_stream() means there is no streams support, so only allowed stream
>> +	 * is the imlicit stream 0.
>> +	 */
>> +	if (streams_mask != BIT_ULL(0))
>> +		return -EOPNOTSUPP;
>> +
>> +	/*
>> +	 * We use a 64-bit bitmask for tracking enabled pads, so only subdevices
>> +	 * with 64 pads or less can be supported.
>> +	 */
>> +	if (pad >= sizeof(sd->enabled_pads) * 8)
> 
> Ditto.
> 
> How much of the code of the two functions is the same? Could some of this
> be put to a common function both would call? They look (almost) exactly the
> same.

v4l2_subdev_enable_streams_fallback and v4l2_subdev_enable_streams? They 
have similar parts, but I don't right away see how combining them or 
making some common functions would help.

  Tomi

> 
>> +		return -EOPNOTSUPP;
>>   
>> -	if ((sd->enabled_streams & streams_mask) != streams_mask) {
>> -		dev_dbg(dev, "set of streams %#llx already disabled on %s:%u\n",
>> -			streams_mask, sd->entity.name, pad);
>> +	if ((sd->enabled_pads & BIT_ULL(pad)) != BIT_ULL(pad)) {
>> +		dev_dbg(dev, "pad %u already disabled on %s\n",
>> +			pad, sd->entity.name);
>>   		return -EALREADY;
>>   	}
>>   
>>   	/* Stop streaming when the last streams are disabled. */
>> -	if (!(sd->enabled_streams & ~streams_mask)) {
>> +	if (!(sd->enabled_pads & ~BIT_ULL(pad))) {
>>   		ret = v4l2_subdev_call(sd, video, s_stream, 0);
>>   		if (ret)
>>   			return ret;
>>   	}
>>   
>> -	sd->enabled_streams &= ~streams_mask;
>> +	sd->enabled_pads &= ~BIT_ULL(pad);
>>   
>>   	return 0;
>>   }
>> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
>> index 8bd1e3c96d2b..7077aec3176c 100644
>> --- a/include/media/v4l2-subdev.h
>> +++ b/include/media/v4l2-subdev.h
>> @@ -1039,10 +1039,9 @@ struct v4l2_subdev_platform_data {
>>    * @active_state: Active state for the subdev (NULL for subdevs tracking the
>>    *		  state internally). Initialized by calling
>>    *		  v4l2_subdev_init_finalize().
>> - * @enabled_streams: Bitmask of enabled streams used by
>> - *		     v4l2_subdev_enable_streams() and
>> - *		     v4l2_subdev_disable_streams() helper functions for fallback
>> - *		     cases.
>> + * @enabled_pads: Bitmask of enabled pads used by 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.
>>    *
>>    * Each instance of a subdev driver should create this struct, either
>> @@ -1091,7 +1090,7 @@ struct v4l2_subdev {
>>   	 * doesn't support it.
>>   	 */
>>   	struct v4l2_subdev_state *active_state;
>> -	u64 enabled_streams;
>> +	u64 enabled_pads;
>>   	bool streaming_enabled;
>>   };
>>   
>>
>