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Date: Thu, 4 Apr 2024 16:47:41 +0300
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Subject: Re: [PATCH 3/4] media: subdev: Improve
 v4l2_subdev_enable/disable_streams_fallback
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>,
 Mauro Carvalho Chehab <mchehab@kernel.org>, Hans Verkuil
 <hverkuil@xs4all.nl>, 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>
 <a5ea5844-a7ba-408b-8007-2000dc94be24@ideasonboard.com>
 <20240404130617.GR23803@pendragon.ideasonboard.com>
From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
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In-Reply-To: <20240404130617.GR23803@pendragon.ideasonboard.com>
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On 04/04/2024 16:06, Laurent Pinchart wrote:
> On Thu, Apr 04, 2024 at 03:38:45PM +0300, Tomi Valkeinen wrote:
>> On 04/04/2024 15:18, Sakari Ailus wrote:
>>> 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.
> 
> s/soruce/source/
> 
>>>>
>>>> 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.
> 
> While at it, s/on/to/

Actually, now that we support multiple pads here... Should the comment 
and the if below, checking whether the pad is a source pad, be removed? 
Is there any reason to require a source pad here (but not in the 
non-fallback case)?

  Tomi


> 
> Same below.
> 
>>>>    	 */
>>>>    	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.
> 
> s/imlicit/implicit/
> 
> Same below.
> 
>>>> +	 */
>>>> +	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.
> 
> You could move the three checks to a
> v4l2_subdev_streams_fallback_check() function (bikeshedding the name is
> allowed).
> 
>>>> +		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)) {
> 
> 	if (!(sd->enabled_pads & 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;
>>>>    };
>>>>    
>