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Date: Wed, 24 Apr 2024 16:09:22 +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: <20240424130922.GG18608@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>
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In-Reply-To: <7ed5e8cf-2bcc-4d4c-a1dc-17592b5909c0@ideasonboard.com>

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 ?

> 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 =).
> 
>   Tomi
> 
> >> +		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