Date: Wed, 24 Apr 2024 16:11:36 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Hans Verkuil <hverkuil@...all.nl>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Umang Jain <umang.jain@...asonboard.com>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 09/10] media: subdev: Support single-stream case in
 v4l2_subdev_enable/disable_streams()

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?

  Tomi

> 
>> 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@...asonboard.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@...asonboard.com>
>>>
>>>>    
>>>> -	v4l2_subdev_unlock_state(state);
>>>> +		v4l2_subdev_unlock_state(state);
>>>> +	}
>>>>    
>>>>    	return ret;
>>>>    }
>>>>
>>>
>>
> 

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