Hi Dennis, On Fri, Jul 16, 2021 at 04:09:21PM +0200, Dennis Rachui wrote: > > On Thu, Jul 15, 2021 at 12:57:37PM +0200, Niklas Söderlund wrote: > > > On 2021-07-14 21:40:51 +0300, Laurent Pinchart wrote: > > > > On Tue, Jul 13, 2021 at 11:42:17AM +0200, Niklas Söderlund wrote: > > > > > On 2021-07-11 01:42:44 +0300, Laurent Pinchart wrote: > > > > > > On Fri, Jul 09, 2021 at 04:20:40PM +0200, Niklas Söderlund wrote: > > > > > > > On 2021-07-08 15:22:58 +0200, Dennis Rachui wrote: > > > > > > > > Verify that streaming is not active before setting the pad format. > > > > > > > > > > > > > > > > According to the VIDIOC documentation [1] changes to the > > > > > > > > active format of a media pad via the VIDIOC_SUBDEV_S_FMT > > > > > > > > ioctl are applied to the underlying hardware. > > > > > > > > In rcar-csi2 a format change only applies to hardware, when > > > > > > > > the pipeline is started. While the device is not in use, it > > > > > > > > is therefore okay to update the format. > > > > > > > > > > > > > > > > However, when the pipeline is active, this leads to a format > > > > > > > > mismatch between driver and device. > > > > > > > > Other applications can query the format with > > > > > > > > VIDIOC_SUBDEV_G_FMT at any time and would be reported a > > > > > > > > format that does not fit the current stream. > > > > > > > > > > > > > > > > This commit prevents format update while streaming is active > > > > > > > > and returns -EBUSY to user space, as suggested by [1]. > > > > > > > > > > > > > > > > [1] > > > > > > > > Documentation/userspace-api/media/v4l/vidioc-subdev-g-fmt.rs > > > > > > > > t > > > > > > > > > > > > > > I like that this is addressed, but I wonder is this not > > > > > > > something that should be fixed in the V4L2 core and not in drivers? > > > > > > > > > > > > Some drivers may support format changes during streaming (that's > > > > > > allowed by the V4L2 API, I'm not sure if it's used anywhere > > > > > > though). While I'd favour not duplicating the same logic in > > > > > > different (and differently > > > > > > buggy) ways in drivers, I'm not sure how this could be > > > > > > implemented in a sane way in the V4L2 core in its current state. > > > > > > > > > > I understand it's possible from some devices to support to format > > > > > changes during streaming, but as you point out it's the exception > > > > > and not the rule, if used at all. > > > > > > > > > > So my point is if we start to enforce this in drivers we are > > > > > headed down a road where this will be messier to clean up. Would > > > > > it not make more sens to default the V4L2 core to disallow format > > > > > changes while streaming and add a new flag to V4L2_SUBDEV_CAP_ to > > > > > signal that the subdevice supports format changes while streaming? > > > > > > > > > > We already have V4L2_SUBDEV_CAP_RO_SUBDEV to signal that a > > > > > subdevice only supports read-only operations so I think it would > > > > > not be too hard to move this functionality into the core? > > > > > > > > Yes, that's something we could try. The subdev core will then need > > > > to track the streaming state, which may require wrapping the > > > > .s_stream() call. Locking should then also likely be handled by the > > > > core. Probably nothing impossible, but quite a bit of work. Any > > > > volunteer ? :-) > > > > > > We already track the stream count in struct media_entity and it's > > > incremented/decremented under the media device lock by > > > media_pipeline_start() and media_pipeline_stop(). So I don't think > > > it's such a hard feature to add. > > > > > > The large task IMHO is to figure out if we have any subdevice in tree > > > that allows format changes while streaming and that would need to set > > > this new V4L2_SUBDEV_CAP_ flag. > > > > Many subdevs allow format changes during streaming. The question is > > whether any of them do so knowingly, or if they're all buggy :-) I'd > > be surprised if there > were more than a couple of drivers that > > actually support this correctly. > > From my perspective, the current stream_count from struct media_entity > would not be sufficient. References should be counted per struct media_pad. > Otherwise, devices that allow multiple parallel streams would block user > space from updating media-pads that are not part of an active media-pipeline. > E.g. in rcar-csi2 this could effect a source pad connected to currently > unused VIN device. We're working on moving the information to pads, see "[PATCH v7 06/27] media: entity: Move the pipeline from entity to pads" (https://lore.kernel.org/linux-media/20210524104408.599645-7-tomi.valkeinen@xxxxxxxxxxxxxxxx/). Does this address your concern ? > > > > > > > > Note: after creation of this commit, it was noticed that > > > > > > > > Steve Longerbeam has a very similar solution in his fork. > > > > > > > > > > > > > > > > Fixes: 769afd212b16 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver") > > > > > > > > Cc: Steve Longerbeam <slongerbeam@xxxxxxxxx> > > > > > > > > Signed-off-by: Dennis Rachui <drachui@xxxxxxxxxxxxxx> > > > > > > > > --- > > > > > > > > drivers/media/platform/rcar-vin/rcar-csi2.c | 21 ++++++++++++++++++++- > > > > > > > > 1 file changed, 20 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > > > > > b/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > > > > > index e28eff0..98152e1 100644 > > > > > > > > --- a/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > > > > > +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > > > > > @@ -724,18 +724,37 @@ static int rcsi2_set_pad_format(struct > > > > > > > > v4l2_subdev *sd, { > > > > > > > > struct rcar_csi2 *priv = sd_to_csi2(sd); > > > > > > > > struct v4l2_mbus_framefmt *framefmt; > > > > > > > > + int ret = 0; > > > > > > > > + > > > > > > > > + mutex_lock(&priv->lock); > > > > > > > > > > > > > > > > if (!rcsi2_code_to_fmt(format->format.code)) > > > > > > > > format->format.code = rcar_csi2_formats[0].code; > > > > > > > > > > > > > > > > if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE) { > > > > > > > > + > > > > > > > > + /* > > > > > > > > + * Do not apply changes to active format while streaming. > > > > > > > > + * > > > > > > > > + * Since video streams could be forwarded from sink pad to any > > > > > > > > + * source pad (depending on CSI-2 channel routing), all > > > > > > > > + * media pads are effected by this rule. > > > > > > > > + */ > > > > > > > > + if (priv->stream_count > 0) { > > > > > > > > + ret = -EBUSY; > > > > > > > > + goto out; > > > > > > > > + } > > > > > > > > + > > > > > > > > priv->mf = format->format; > > > > > > > > } else { > > > > > > > > framefmt = v4l2_subdev_get_try_format(sd, sd_state, 0); > > > > > > > > *framefmt = format->format; > > > > > > > > } > > > > > > > > > > > > > > > > - return 0; > > > > > > > > +out: > > > > > > > > + mutex_unlock(&priv->lock); > > > > > > > > + > > > > > > > > + return ret; > > > > > > > > } > > > > > > > > > > > > > > > > static int rcsi2_get_pad_format(struct v4l2_subdev *sd, -- Regards, Laurent Pinchart
