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Message-ID: <20240424130922.GG18608@pendragon.ideasonboard.com>
Date: Wed, 24 Apr 2024 16:09:22 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...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 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@...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;
> >> }
> >>
> >
>
--
Regards,
Laurent Pinchart
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