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Date: Thu, 4 Apr 2024 17:25:14 +0300
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@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
Subject: Re: [PATCH 3/4] media: subdev: Improve
 v4l2_subdev_enable/disable_streams_fallback
Message-ID: <20240404142514.GT23803@pendragon.ideasonboard.com>
References: <20240404-enable-streams-impro-v1-0-1017a35bbe07@ideasonboard.com>
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 <Zg6anfpQt80gSKjN@kekkonen.localdomain>
 <a5ea5844-a7ba-408b-8007-2000dc94be24@ideasonboard.com>
 <20240404130617.GR23803@pendragon.ideasonboard.com>
 <e26e1251-de1d-4c86-9041-a5e3b2e2d765@ideasonboard.com>
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In-Reply-To: <e26e1251-de1d-4c86-9041-a5e3b2e2d765@ideasonboard.com>

On Thu, Apr 04, 2024 at 04:47:41PM +0300, Tomi Valkeinen wrote:
> 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)?

Mostly the lack of test platforms where we handle stream start/stop from
source to sink, calling the operations on sink pads. I'm sure there will
be unforeseen issues :-)

> > 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;
> >>>>    };
> >>>>    

-- 
Regards,

Laurent Pinchart