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Date: Wed, 24 Apr 2024 16:17:33 +0300
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Umang Jain <umang.jain@ideasonboard.com>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 09/10] media: subdev: Support single-stream case in
 v4l2_subdev_enable/disable_streams()
Message-ID: <20240424131733.GH18608@pendragon.ideasonboard.com>
References: <20240416-enable-streams-impro-v5-0-bd5fcea49388@ideasonboard.com>
 <20240416-enable-streams-impro-v5-9-bd5fcea49388@ideasonboard.com>
 <20240419153603.GE12651@pendragon.ideasonboard.com>
 <7ed5e8cf-2bcc-4d4c-a1dc-17592b5909c0@ideasonboard.com>
 <20240424130922.GG18608@pendragon.ideasonboard.com>
 <6e2eeba1-236f-481e-9e35-460f26549698@ideasonboard.com>
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In-Reply-To: <6e2eeba1-236f-481e-9e35-460f26549698@ideasonboard.com>

On Wed, Apr 24, 2024 at 04:11:36PM +0300, Tomi Valkeinen wrote:
> On 24/04/2024 16:09, Laurent Pinchart wrote:
> > On Wed, Apr 24, 2024 at 04:05:31PM +0300, Tomi Valkeinen wrote:
> >> On 19/04/2024 18:36, Laurent Pinchart wrote:
> >>> On Tue, Apr 16, 2024 at 04:55:12PM +0300, Tomi Valkeinen wrote:
> >>>> At the moment the v4l2_subdev_enable/disable_streams() functions call
> >>>> fallback helpers to handle the case where the subdev only implements
> >>>> .s_stream(), and the main function handles the case where the subdev
> >>>> implements streams (V4L2_SUBDEV_FL_STREAMS, which implies
> >>>> .enable/disable_streams()).
> >>>>
> >>>> What is missing is support for subdevs which do not implement streams
> >>>> support, but do implement .enable/disable_streams(). Example cases of
> >>>> these subdevices are single-stream cameras, where using
> >>>> .enable/disable_streams() is not required but helps us remove the users
> >>>> of the legacy .s_stream(), and subdevices with multiple source pads (but
> >>>> single stream per pad), where .enable/disable_streams() allows the
> >>>> subdevice to control the enable/disable state per pad.
> >>>>
> >>>> The two single-streams cases (.s_stream() and .enable/disable_streams())
> >>>> are very similar, and with small changes we can change the
> >>>> v4l2_subdev_enable/disable_streams() functions to support all three
> >>>> cases, without needing separate fallback functions.
> >>>>
> >>>> A few potentially problematic details, though:
> >>>>
> >>>> - For the single-streams cases we use sd->enabled_pads field, which
> >>>>     limits the number of pads for the subdevice to 64. For simplicity I
> >>>>     added the check for this limitation to the beginning of the function,
> >>>>     and it also applies to the streams case.
> >>>>
> >>>> - The fallback functions only allowed the target pad to be a source pad.
> >>>>     It is not very clear to me why this check was needed, but it was not
> >>>>     needed in the streams case. However, I doubt the
> >>>>     v4l2_subdev_enable/disable_streams() code has ever been tested with
> >>>>     sink pads, so to be on the safe side, I added the same check
> >>>>     to the v4l2_subdev_enable/disable_streams() functions.
> >>>>
> >>>
> >>> Now that v4l2_subdev_enable_streams() is usable by (almost) every
> >>> driver, should we update documentation to indicate that manual calls to
> >>> .s_stream() should be avoided ?
> >>
> >> How about:
> >>
> >> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> >> index dabe1b5dfe4a..f52bb790773c 100644
> >> --- a/include/media/v4l2-subdev.h
> >> +++ b/include/media/v4l2-subdev.h
> >> @@ -450,6 +450,11 @@ enum v4l2_subdev_pre_streamon_flags {
> >>    *     already started or stopped subdev. Also see call_s_stream wrapper in
> >>    *     v4l2-subdev.c.
> >>    *
> >> + *     New drivers should instead implement &v4l2_subdev_pad_ops.enable_streams
> >> + *     and &v4l2_subdev_pad_ops.disable_streams operations, and use
> >> + *     v4l2_subdev_s_stream_helper for the &v4l2_subdev_video_ops.s_stream
> >> + *     operation to support legacy users.A
> >> + *
> > 
> > Add
> > 
> >   *	Drivers should also not call the .s_stream() subdev operation directly,
> >   *	but use the v4l2_subdev_enable_streams() and
> >   *	v4l2_subdev_disable_streams() helpers.
> > 
> >>    * @g_pixelaspect: callback to return the pixelaspect ratio.
> >>    *
> >>    * @s_dv_timings: Set custom dv timings in the sub device. This is used
> >>
> >>
> >> Although now that I think about it, can we "ever" get rid of s_stream?
> >> enable_streams is only usable if the subdev has pads.
> > 
> > Do we have pad-less subdevs that can stream ?
> 
> Probably not, but isn't s_stream used to enable any type of subdev? Or 
> is there a different op to power on padless subdevs?

s_stream() is supposed to start/stop streaming, and you can't really
have streams without pads, as they have to come from/go somewhere.

> >> If that's the
> >> case, the text above should probably clarify when one should continue
> >> using s_stream.
> >>
> >>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> >>>> ---
> >>>>    drivers/media/v4l2-core/v4l2-subdev.c | 187 ++++++++++++++--------------------
> >>>>    1 file changed, 79 insertions(+), 108 deletions(-)
> >>>>
> >>>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> >>>> index e45fd42da1e3..10406acfb9d0 100644
> >>>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> >>>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> >>>> @@ -2106,6 +2106,13 @@ static void v4l2_subdev_collect_streams(struct v4l2_subdev *sd,
> >>>>    					u64 *found_streams,
> >>>>    					u64 *enabled_streams)
> >>>>    {
> >>>> +	if (!(sd->flags & V4L2_SUBDEV_FL_STREAMS)) {
> >>>> +		*found_streams = BIT_ULL(0);
> >>>> +		*enabled_streams =
> >>>> +			(sd->enabled_pads & BIT_ULL(pad)) ? BIT_ULL(0) : 0;
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>>    	*found_streams = 0;
> >>>>    	*enabled_streams = 0;
> >>>>    
> >>>> @@ -2127,6 +2134,14 @@ static void v4l2_subdev_set_streams_enabled(struct v4l2_subdev *sd,
> >>>>    					    u32 pad, u64 streams_mask,
> >>>>    					    bool enabled)
> >>>>    {
> >>>> +	if (!(sd->flags & V4L2_SUBDEV_FL_STREAMS)) {
> >>>> +		if (enabled)
> >>>> +			sd->enabled_pads |= BIT_ULL(pad);
> >>>> +		else
> >>>> +			sd->enabled_pads &= ~BIT_ULL(pad);
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>>    	for (unsigned int i = 0; i < state->stream_configs.num_configs; ++i) {
> >>>>    		struct v4l2_subdev_stream_config *cfg =
> >>>>    			&state->stream_configs.configs[i];
> >>>> @@ -2136,51 +2151,6 @@ static void v4l2_subdev_set_streams_enabled(struct v4l2_subdev *sd,
> >>>>    	}
> >>>>    }
> >>>>    
> >>>> -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;
> >>>> -	int ret;
> >>>> -
> >>>> -	/*
> >>>> -	 * The subdev doesn't implement pad-based stream enable, fall back
> >>>> -	 * to the .s_stream() operation.
> >>>> -	 */
> >>>> -	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
> >>>> -		return -EOPNOTSUPP;
> >>>> -
> >>>> -	/*
> >>>> -	 * .s_stream() means there is no streams support, so the only allowed
> >>>> -	 * stream is the implicit 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) * BITS_PER_BYTE)
> >>>> -		return -EOPNOTSUPP;
> >>>> -
> >>>> -	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 pad is enabled. */
> >>>> -	if (!sd->enabled_pads) {
> >>>> -		ret = v4l2_subdev_call(sd, video, s_stream, 1);
> >>>> -		if (ret)
> >>>> -			return ret;
> >>>> -	}
> >>>> -
> >>>> -	sd->enabled_pads |= BIT_ULL(pad);
> >>>> -
> >>>> -	return 0;
> >>>> -}
> >>>> -
> >>>>    int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    			       u64 streams_mask)
> >>>>    {
> >>>> @@ -2189,21 +2159,33 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    	bool already_streaming;
> >>>>    	u64 enabled_streams;
> >>>>    	u64 found_streams;
> >>>> +	bool use_s_stream;
> >>>>    	int ret;
> >>>>    
> >>>>    	/* A few basic sanity checks first. */
> >>>>    	if (pad >= sd->entity.num_pads)
> >>>>    		return -EINVAL;
> >>>>    
> >>>> +	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
> >>>> +		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) * BITS_PER_BYTE)
> >>>> +		return -EOPNOTSUPP;
> >>>> +
> >>>>    	if (!streams_mask)
> >>>>    		return 0;
> >>>>    
> >>>>    	/* Fallback on .s_stream() if .enable_streams() isn't available. */
> >>>> -	if (!v4l2_subdev_has_op(sd, pad, enable_streams))
> >>>> -		return v4l2_subdev_enable_streams_fallback(sd, pad,
> >>>> -							   streams_mask);
> >>>> +	use_s_stream = !v4l2_subdev_has_op(sd, pad, enable_streams);
> >>>>    
> >>>> -	state = v4l2_subdev_lock_and_get_active_state(sd);
> >>>> +	if (!use_s_stream)
> >>>> +		state = v4l2_subdev_lock_and_get_active_state(sd);
> >>>> +	else
> >>>> +		state = NULL;
> >>>>    
> >>>>    	/*
> >>>>    	 * Verify that the requested streams exist and that they are not
> >>>> @@ -2231,9 +2213,18 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    
> >>>>    	already_streaming = v4l2_subdev_is_streaming(sd);
> >>>>    
> >>>> -	/* Call the .enable_streams() operation. */
> >>>> -	ret = v4l2_subdev_call(sd, pad, enable_streams, state, pad,
> >>>> -			       streams_mask);
> >>>> +	if (!use_s_stream) {
> >>>> +		/* Call the .enable_streams() operation. */
> >>>> +		ret = v4l2_subdev_call(sd, pad, enable_streams, state, pad,
> >>>> +				       streams_mask);
> >>>> +	} else {
> >>>> +		/* Start streaming when the first pad is enabled. */
> >>>> +		if (!already_streaming)
> >>>> +			ret = v4l2_subdev_call(sd, video, s_stream, 1);
> >>>> +		else
> >>>> +			ret = 0;
> >>>> +	}
> >>>> +
> >>>>    	if (ret) {
> >>>>    		dev_dbg(dev, "enable streams %u:%#llx failed: %d\n", pad,
> >>>>    			streams_mask, ret);
> >>>> @@ -2243,34 +2234,32 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    	/* Mark the streams as enabled. */
> >>>>    	v4l2_subdev_set_streams_enabled(sd, state, pad, streams_mask, true);
> >>>
> >>> state gets set to a non-null value above if the subdev has an
> >>> enable_streams operation, while in v4l2_subdev_set_streams_enabled(),
> >>
> >> That's not quite true, v4l2_subdev_lock_and_get_active_state() returns
> >> NULL if there's no state. If the driver has .enable_streams but no
> >> subdev-state, we'll have NULL state. But is that a driver bug? Probably,
> >> although I'm not quite sure. Whereas V4L2_SUBDEV_FL_STREAMS without
> >> state is a driver bug.
> >>
> >>> you use it if the V4L2_SUBDEV_FL_STREAMS flag is set. The second
> >>> condition is a subset of the first one, so it should be safe now, but I
> >>> wonder if we're at risk of crashes in the future when reworking the
> >>> code. I'm probably worrying needlessly.
> >>
> >> I agree that this is a bit messy. We have multiple different scenarios
> >> which we handle in the same functions, and it's somewhat unclear what
> >> op/state/flag combinations the drivers are allowed to have and what not.
> >>
> >> I could add a !state check here, and then use sd->enabled_pads. But that
> >> doesn't feel correct, and I think it's just better to crash and then fix
> >> it if we end up there.
> >>
> >>>>    
> >>>> -	if (!already_streaming)
> >>>> +	if (!use_s_stream && !already_streaming)
> >>>>    		v4l2_subdev_enable_privacy_led(sd);
> >>>
> >>> Once everybody switches to v4l2_subdev_enable_streams() (am I dreaming?)
> >>> we should move LED handling from the .s_stream() wrapper to here for the
> >>> fallback case too. How about a TODO comment ?
> >>
> >> Let's get back to this after we figure out if s_stream can ever be removed.
> >>
> >>>>    
> >>>>    done:
> >>>> -	v4l2_subdev_unlock_state(state);
> >>>> +	if (!use_s_stream)
> >>>
> >>> 	if (state)
> >>>
> >>> would be better I think.
> >>
> >> We get the state and state lock if (!use_s_stream), so I think it makes
> >> sense to use the same condition when unlocking to be symmetric. I'm sure
> >> I can be convinced to use if (state) too, though =).
> >>
> >>>> +		v4l2_subdev_unlock_state(state);
> >>>>    
> >>>>    	return ret;
> >>>>    }
> >>>>    EXPORT_SYMBOL_GPL(v4l2_subdev_enable_streams);
> >>>>    
> >>>> -static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
> >>>> -						u64 streams_mask)
> >>>> +int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>> +				u64 streams_mask)
> >>>>    {
> >>>>    	struct device *dev = sd->entity.graph_obj.mdev->dev;
> >>>> +	struct v4l2_subdev_state *state;
> >>>> +	u64 enabled_streams;
> >>>> +	u64 found_streams;
> >>>> +	bool use_s_stream;
> >>>>    	int ret;
> >>>>    
> >>>> -	/*
> >>>> -	 * If the subdev doesn't implement pad-based stream enable, fall back
> >>>> -	 * to the .s_stream() operation.
> >>>> -	 */
> >>>> -	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
> >>>> -		return -EOPNOTSUPP;
> >>>> +	/* A few basic sanity checks first. */
> >>>> +	if (pad >= sd->entity.num_pads)
> >>>> +		return -EINVAL;
> >>>>    
> >>>> -	/*
> >>>> -	 * .s_stream() means there is no streams support, so the only allowed
> >>>> -	 * stream is the implicit stream 0.
> >>>> -	 */
> >>>> -	if (streams_mask != BIT_ULL(0))
> >>>> +	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
> >>>>    		return -EOPNOTSUPP;
> >>>>    
> >>>>    	/*
> >>>> @@ -2280,46 +2269,16 @@ static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
> >>>>    	if (pad >= sizeof(sd->enabled_pads) * BITS_PER_BYTE)
> >>>>    		return -EOPNOTSUPP;
> >>>>    
> >>>> -	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_pads & ~BIT_ULL(pad))) {
> >>>> -		ret = v4l2_subdev_call(sd, video, s_stream, 0);
> >>>> -		if (ret)
> >>>> -			return ret;
> >>>> -	}
> >>>> -
> >>>> -	sd->enabled_pads &= ~BIT_ULL(pad);
> >>>> -
> >>>> -	return 0;
> >>>> -}
> >>>> -
> >>>> -int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>> -				u64 streams_mask)
> >>>> -{
> >>>> -	struct device *dev = sd->entity.graph_obj.mdev->dev;
> >>>> -	struct v4l2_subdev_state *state;
> >>>> -	u64 enabled_streams;
> >>>> -	u64 found_streams;
> >>>> -	int ret;
> >>>> -
> >>>> -	/* A few basic sanity checks first. */
> >>>> -	if (pad >= sd->entity.num_pads)
> >>>> -		return -EINVAL;
> >>>> -
> >>>>    	if (!streams_mask)
> >>>>    		return 0;
> >>>>    
> >>>>    	/* Fallback on .s_stream() if .disable_streams() isn't available. */
> >>>> -	if (!v4l2_subdev_has_op(sd, pad, disable_streams))
> >>>> -		return v4l2_subdev_disable_streams_fallback(sd, pad,
> >>>> -							    streams_mask);
> >>>> +	use_s_stream = !v4l2_subdev_has_op(sd, pad, disable_streams);
> >>>>    
> >>>> -	state = v4l2_subdev_lock_and_get_active_state(sd);
> >>>> +	if (!use_s_stream)
> >>>> +		state = v4l2_subdev_lock_and_get_active_state(sd);
> >>>> +	else
> >>>> +		state = NULL;
> >>>>    
> >>>>    	/*
> >>>>    	 * Verify that the requested streams exist and that they are not
> >>>> @@ -2345,9 +2304,19 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    
> >>>>    	dev_dbg(dev, "disable streams %u:%#llx\n", pad, streams_mask);
> >>>>    
> >>>> -	/* Call the .disable_streams() operation. */
> >>>> -	ret = v4l2_subdev_call(sd, pad, disable_streams, state, pad,
> >>>> -			       streams_mask);
> >>>> +	if (!use_s_stream) {
> >>>> +		/* Call the .disable_streams() operation. */
> >>>> +		ret = v4l2_subdev_call(sd, pad, disable_streams, state, pad,
> >>>> +				       streams_mask);
> >>>> +	} else {
> >>>> +		/* Stop streaming when the last streams are disabled. */
> >>>> +
> >>>> +		if (!(sd->enabled_pads & ~BIT_ULL(pad)))
> >>>> +			ret = v4l2_subdev_call(sd, video, s_stream, 0);
> >>>> +		else
> >>>> +			ret = 0;
> >>>> +	}
> >>>> +
> >>>>    	if (ret) {
> >>>>    		dev_dbg(dev, "disable streams %u:%#llx failed: %d\n", pad,
> >>>>    			streams_mask, ret);
> >>>> @@ -2357,10 +2326,12 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
> >>>>    	v4l2_subdev_set_streams_enabled(sd, state, pad, streams_mask, false);
> >>>>    
> >>>>    done:
> >>>> -	if (!v4l2_subdev_is_streaming(sd))
> >>>> -		v4l2_subdev_disable_privacy_led(sd);
> >>>> +	if (!use_s_stream) {
> >>>> +		if (!v4l2_subdev_is_streaming(sd))
> >>>> +			v4l2_subdev_disable_privacy_led(sd);
> >>>
> >>> Do we want to disable the privacy LED on failure in all cases, in
> >>> particular when the .s_stream() or .disable_streams() operations are not
> >>> even called ?
> >>>
> >>> And now that I wrote that, I realize the !v4l2_subdev_is_streaming()
> >>> condition will not be true if the operations failed, so it should be
> >>> fine.
> >>>
> >>> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >>>
> >>>>    
> >>>> -	v4l2_subdev_unlock_state(state);
> >>>> +		v4l2_subdev_unlock_state(state);
> >>>> +	}
> >>>>    
> >>>>    	return ret;
> >>>>    }
> >>>>

-- 
Regards,

Laurent Pinchart