Hi Michael,
Thanks for your feedback.
On 2022-03-02 17:48:34 +0100, Michael Rodin wrote:
> Hi Niklas, Hans,
>
> On Mon, Nov 15, 2021 at 03:26:53PM +0100, Hans Verkuil wrote:
> > On 08/11/2021 19:42, Niklas Söderlund wrote:
> > > Hi Hans,
> > >
> > > On 2021-11-08 18:36:25 +0100, Hans Verkuil wrote:
> > >> On 08/11/2021 17:02, Niklas Söderlund wrote:
> > >>> When a subdevice signals a transfer error stop the VIN in addition to
> > >>> informing user-space of the event.
> > >>>
> > >>> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> > >>> Reviewed-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> > >>> ---
> > >>> * Changes since v3
> > >>> - Switch to new V4L2_EVENT_XFER_ERROR from V4L2_EVENT_EOS.
> > >>> - Call vb2_queue_error() when encountering the event.
> > >>>
> > >>> * Changes since v2
> > >>> - Log using vin_dbg() instead of v4l2_info().
> > >>> ---
> > >>> drivers/media/platform/rcar-vin/rcar-v4l2.c | 17 ++++++++++++++++-
> > >>> 1 file changed, 16 insertions(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/drivers/media/platform/rcar-vin/rcar-v4l2.c b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > >>> index a5bfa76fdac6e55a..bf17fdefe90aabf5 100644
> > >>> --- a/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > >>> +++ b/drivers/media/platform/rcar-vin/rcar-v4l2.c
> > >>> @@ -992,9 +992,24 @@ void rvin_v4l2_unregister(struct rvin_dev *vin)
> > >>> static void rvin_notify_video_device(struct rvin_dev *vin,
> > >>> unsigned int notification, void *arg)
> > >>> {
> > >>> + const struct v4l2_event *event;
> > >>> +
> > >>> switch (notification) {
> > >>> case V4L2_DEVICE_NOTIFY_EVENT:
> > >>> - v4l2_event_queue(&vin->vdev, arg);
> > >>> + event = arg;
> > >>> +
> > >>> + switch (event->type) {
> > >>> + case V4L2_EVENT_XFER_ERROR:
> > >>> + vin_dbg(vin,
> > >>> + "Subdevice signaled transfer error, stopping.\n");
> > >>> + rvin_stop_streaming(vin);
> > >>> + vb2_queue_error(&vin->queue);
> > >>
> > >> Hmm, wouldn't it be the case that every driver that calls vb2_queue_error()
> > >> would also have to send this new event? Would it be possible to modify
> > >> vb2_queue_error() to raise this event? I haven't analyzed all the drivers
> > >> that call this function to see if that makes sense.
> > >>
> > >> Perhaps a separate new function vb2_queue_error_with_event() would also be
> > >> an option.
> > >
> > > I think that maybe a good idea, but I think that would be needed on-top
> > > of this work as I can't really test it. Here the rcar-csi2.ko is a
> > > subdevice which detects the error condition and generates the event. And
> > > this code is in rcar-vin.ko, the video device driver which reacts to the
> > > event and then forwards it to user-space.
> > >
> > > Or am I misunderstanding you? And you think I should remove the
> > > v4l2_event_queue() below in favor of a new vb2_queue_error_with_event()
> > > call?
> >
> > Yes. And use vb2_queue_error_with_event in other drivers as well where
> > applicable. Hmm, it can't be called vb2_ since it is v4l2_ specific, so
> > perhaps v4l2_queue_error which takes a video_device and a vb2_queue as
> > arguments. I don't want this just in rcar since it makes perfect sense
> > as a generic event for such situations.
>
> Handling errors in this way could be problematic, because a (CSI2) transfer
> error does not mean a total hardware failure on Rcar3. From my experience
> there are 3 kinds of CSI2 errors:
> 1. errors which occur sometimes, but do not affect video streaming
> 2. errors which occur on every start of streaming but usually do not
> affect actual video streaming to VIN module after the start
> 3. fatal errors which require a "Software Reset" mentioned by Renesas in
> the chapter 25.3.13 of the hardware manual in order to continue
> video streaming
> This patch set makes the video pipeline unusable if we get errors described
> in the first scenario if I am not mistaken. In the second scenario the
> video pipeline was already not usable before because we end up in a
> continuous restart loop in rcar-csi2.c. And the third scenario is not
> really addressed by this patch set (or maybe the job is offloaded on to
> userspace)?
>
> Maybe it's better to implement a recovery in a different way, which would
> consider the three mentioned error scenarios above:
> 1. Monitor rvin_irq after streaming has started, e.g. by using a timer
> (I tried someting similar in [1])
> 2. restart the complete video pipeline via rvin_stop_streaming and
> rvin_start_streaming if no frame is captured in a reasonable amount
> of time (optionally after checking if a subdevice has sent a
> V4L2_EVENT_XFER_ERROR).
> This would make the complete recovery process almost invisible for the
> application and avoid any application changes.
>
> What do you think?
I think you bring up a few interesting points and for discussions sake I
think we need to split it in two. One on how we could implement
V4L2_EVENT_XFER_ERROR in a generic sens and one on how to best deal with
errors in the R-Car Gen3 capture pipeline.
For the proposed V4L2_EVENT_XFER_ERROR the idea from my side is that a
driver in the pipeline shall only raise this error (and propagate it to
the effected video node) when there is no way to recover without
involving user-space. So when this event happens an application at the
very least needs to do a full s_stream cycle to restart the capture
session.
On the particulars of the VIN capture pipeline the only way I found so
far to freak out the CSI-2 receiver enough to trigger the event with this
patch series is to disconnect the HDMI source from the ADV7481 while
streaming and I don't think any in kernel recover method can fix that
;-)
Over all I do agree with your idea that if we can recover from errors
that are recovererable that is good. For this series I would like to
focus on the former to get V4L2_EVENT_XFER_ERROR in and then if we have
ways to provoke and test recovery in the Gen3 pipeline we can add such
things to the drivers. Do this make sens or do you think the change in
the R-Car CSI-2 driver to raise V4L2_EVENT_XFER_ERROR is to harsh? My
motivation for is is the new datasheet and discussions with Renesas, but
then again my only way to trigger CSI-2 errors is to pull cables while
streaming so maybe I'm biased as such issues can't really be recover
from...
Let me know what you think, I was about to spin a new version of this
series.
>
> [1] https://lore.kernel.org/linux-renesas-soc/1592588777-100596-1-git-send-email-mrodin@xxxxxxxxxxxxxx/
>
> > Regards,
> >
> > Hans
> >
> > >
> > >>
> > >> Regards,
> > >>
> > >> Hans
> > >>
> > >>> + break;
> > >>> + default:
> > >>> + break;
> > >>> + }
> > >>> +
> > >>> + v4l2_event_queue(&vin->vdev, event);
> > >>> break;
> > >>> default:
> > >>> break;
> > >>>
> > >>
> > >
> >
>
> --
> Best Regards,
> Michael
--
Kind Regards,
Niklas Söderlund
