Message-ID: <20220520195041.GA18056@vmlxhi-121.adit-jv.com>
Date:   Fri, 20 May 2022 21:50:41 +0200
From:   Michael Rodin <mrodin@...adit-jv.com>
To:     Niklas Söderlund <niklas.soderlund@...natech.se>
CC:     Michael Rodin <mrodin@...adit-jv.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-renesas-soc@...r.kernel.org>, <michael@...in.online>,
        <erosca@...adit-jv.com>
Subject: Re: [PATCH 3/3] rcar-vin: handle transfer errors from subdevices and
 stop streaming if required

Hi Niklas,

On Thu, May 19, 2022 at 11:00:20PM +0200, Niklas Söderlund wrote:
> Hi Michael,
> 
> Thanks for your work.
> 
> I like this patch, I think it captures the issue discussed in the 
> previous thread quiet nicely. One small nit below.
> 
> On 2022-05-19 20:00:09 +0200, Michael Rodin wrote:
> > When a subdevice sends a transfer error event during streaming and we can
> > not capture new frames, then we know for sure that this is an unrecoverable
> > failure and not just a temporary glitch. In this case we can not ignore the
> > transfer error any more and have to notify userspace. In response to the
> > transfer error event userspace can try to restart streaming and hope that
> > it works again.
> > 
> > This patch is based on the patch [1] from Niklas Söderlund, however it adds
> > more logic to check whether the VIN hardware module is actually affected by
> > the transfer errors reported by the usptream device. For this it takes some
> > ideas from the imx driver where EOF interrupts are monitored by the
> > eof_timeout_timer added by commit 4a34ec8e470c ("[media] media: imx: Add
> > CSI subdev driver").
> > 
> > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_linux-2Drenesas-2Dsoc_20211108160220.767586-2D4-2Dniklas.soderlund-2Brenesas-40ragnatech.se_&d=DwIDAw&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=sWsgk3pKkv5GeIDM2RZlPY8TjNFU2D0oBeOj6QNBadE&m=on7B_2z5sGrhiuvQgbA4XC0_qMRWNTZoWGRMzD9N0Ag&s=_LetePiuy8odH72QwAj6k-I0YOANjzkNwTnqqFr0_ck&e=
> > 
> > Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
> > ---
> >  drivers/media/platform/renesas/rcar-vin/rcar-dma.c | 34 ++++++++++++++++++++++
> >  .../media/platform/renesas/rcar-vin/rcar-v4l2.c    | 18 +++++++++++-
> >  drivers/media/platform/renesas/rcar-vin/rcar-vin.h |  7 +++++
> >  3 files changed, 58 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/platform/renesas/rcar-vin/rcar-dma.c b/drivers/media/platform/renesas/rcar-vin/rcar-dma.c
> > index 2272f1c..596a367 100644
> > --- a/drivers/media/platform/renesas/rcar-vin/rcar-dma.c
> > +++ b/drivers/media/platform/renesas/rcar-vin/rcar-dma.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/pm_runtime.h>
> > +#include <media/v4l2-event.h>
> >  
> >  #include <media/videobuf2-dma-contig.h>
> >  
> > @@ -1060,6 +1061,9 @@ static irqreturn_t rvin_irq(int irq, void *data)
> >  		vin_dbg(vin, "Dropping frame %u\n", vin->sequence);
> >  	}
> >  
> > +	cancel_delayed_work(&vin->frame_timeout);
> > +	schedule_delayed_work(&vin->frame_timeout, msecs_to_jiffies(FRAME_TIMEOUT_MS));
> > +
> >  	vin->sequence++;
> >  
> >  	/* Prepare for next frame */
> > @@ -1283,6 +1287,7 @@ int rvin_start_streaming(struct rvin_dev *vin)
> >  	spin_lock_irqsave(&vin->qlock, flags);
> >  
> >  	vin->sequence = 0;
> > +	vin->xfer_error = false;
> >  
> >  	ret = rvin_capture_start(vin);
> >  	if (ret)
> > @@ -1290,6 +1295,10 @@ int rvin_start_streaming(struct rvin_dev *vin)
> >  
> >  	spin_unlock_irqrestore(&vin->qlock, flags);
> >  
> > +	/* We start the frame watchdog only after we have successfully started streaming */
> > +	if (!ret)
> > +		schedule_delayed_work(&vin->frame_timeout, msecs_to_jiffies(FRAME_TIMEOUT_MS));
> > +
> >  	return ret;
> >  }
> >  
> > @@ -1332,6 +1341,12 @@ void rvin_stop_streaming(struct rvin_dev *vin)
> >  	}
> >  
> >  	vin->state = STOPPING;
> > +	/*
> > +	 * Since we are now stopping and don't expect more frames to be captured, make sure that
> > +	 * there is no pending work for error handling.
> > +	 */
> > +	cancel_delayed_work_sync(&vin->frame_timeout);
> > +	vin->xfer_error = false;
> 
> Do we need to set xfer_error to false here? The delayed work is canceled 
> and we reset the xfer_error when we start in rvin_start_streaming().
> 

You are right, this seems to be redundant. But I think that there might be
a different case where we have to reset xfer_error:

 1. A non-critical transfer error has occurred during streaming from a
    HDMI source.
 2. Frames are still captured for an hour without any further problems,
    since it was just a short glitch
 3. Now the source (e.g. HDMI signal generator) has been powered off by the
    user so it does not send new frames.
 4. Timeout occurs due to 3 but since xfer_error has been set 1 hour ago,
    userspace is notified about a transfer error and assumes that streaming
    has been stopped because of this.

To avoid this scenario I think maybe we have to restrict validity of
xfer_error. Maybe it would be better to make xfer_error a counter which is
set after a transfer error to e.g. 10 frames and then decremented after
each captured frame so after 10 successfully captured frames we know that a
timeout has occurred definitely not due to a transfer error?

Another possible improvement might be to make FRAME_TIMEOUT_MS configurable,
maybe via a v4l2 control from userspace? Or we could also define the timeout
as a multiple of the frame interval of the source. This would allow us to
reduce the timeout further based on the particular source so the userspace
does not have to wait for a second until it knows that it has to restart
streaming.

What do you think?

> >  
> >  	/* Wait until only scratch buffer is used, max 3 interrupts. */
> >  	retries = 0;
> > @@ -1424,6 +1439,23 @@ void rvin_dma_unregister(struct rvin_dev *vin)
> >  	v4l2_device_unregister(&vin->v4l2_dev);
> >  }
> >  
> > +static void rvin_frame_timeout(struct work_struct *work)
> > +{
> > +	struct delayed_work *dwork = to_delayed_work(work);
> > +	struct rvin_dev *vin = container_of(dwork, struct rvin_dev, frame_timeout);
> > +	struct v4l2_event event = {
> > +		.type = V4L2_EVENT_XFER_ERROR,
> > +	};
> > +
> > +	vin_dbg(vin, "Frame timeout!\n");
> > +
> > +	if (!vin->xfer_error)
> > +		return;
> > +	vin_err(vin, "Unrecoverable transfer error detected, stopping streaming\n");
> > +	vb2_queue_error(&vin->queue);
> > +	v4l2_event_queue(&vin->vdev, &event);
> > +}
> > +
> >  int rvin_dma_register(struct rvin_dev *vin, int irq)
> >  {
> >  	struct vb2_queue *q = &vin->queue;
> > @@ -1470,6 +1502,8 @@ int rvin_dma_register(struct rvin_dev *vin, int irq)
> >  		goto error;
> >  	}
> >  
> > +	INIT_DELAYED_WORK(&vin->frame_timeout, rvin_frame_timeout);
> > +
> >  	return 0;
> >  error:
> >  	rvin_dma_unregister(vin);
> > diff --git a/drivers/media/platform/renesas/rcar-vin/rcar-v4l2.c b/drivers/media/platform/renesas/rcar-vin/rcar-v4l2.c
> > index 2e2aa9d..bd7f6fe2 100644
> > --- a/drivers/media/platform/renesas/rcar-vin/rcar-v4l2.c
> > +++ b/drivers/media/platform/renesas/rcar-vin/rcar-v4l2.c
> > @@ -648,6 +648,8 @@ static int rvin_subscribe_event(struct v4l2_fh *fh,
> >  	switch (sub->type) {
> >  	case V4L2_EVENT_SOURCE_CHANGE:
> >  		return v4l2_event_subscribe(fh, sub, 4, NULL);
> > +	case V4L2_EVENT_XFER_ERROR:
> > +		return v4l2_event_subscribe(fh, sub, 1, NULL);
> >  	}
> >  	return v4l2_ctrl_subscribe_event(fh, sub);
> >  }
> > @@ -1000,9 +1002,23 @@ 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:
> > +			if (vin->state != STOPPED && vin->state != STOPPING) {
> > +				vin_dbg(vin, "Subdevice signaled transfer error.\n");
> > +				vin->xfer_error = true;
> > +			}
> > +			break;
> > +		default:
> > +			break;
> > +		}
> > +
> >  		break;
> >  	default:
> >  		break;
> > diff --git a/drivers/media/platform/renesas/rcar-vin/rcar-vin.h b/drivers/media/platform/renesas/rcar-vin/rcar-vin.h
> > index 1f94589..4726a69 100644
> > --- a/drivers/media/platform/renesas/rcar-vin/rcar-vin.h
> > +++ b/drivers/media/platform/renesas/rcar-vin/rcar-vin.h
> > @@ -31,6 +31,9 @@
> >  /* Max number on VIN instances that can be in a system */
> >  #define RCAR_VIN_NUM 32
> >  
> > +/* maximum time we wait before signalling an error to userspace */
> > +#define FRAME_TIMEOUT_MS 1000
> > +
> >  struct rvin_group;
> >  
> >  enum model_id {
> > @@ -207,6 +210,8 @@ struct rvin_info {
> >   * @std:		active video standard of the video source
> >   *
> >   * @alpha:		Alpha component to fill in for supported pixel formats
> > + * @xfer_error:		Indicates if any transfer errors occurred in the current streaming session.
> > + * @frame_timeout:	Watchdog for monitoring regular capturing of frames in rvin_irq.
> >   */
> >  struct rvin_dev {
> >  	struct device *dev;
> > @@ -251,6 +256,8 @@ struct rvin_dev {
> >  	v4l2_std_id std;
> >  
> >  	unsigned int alpha;
> > +	bool xfer_error;
> > +	struct delayed_work frame_timeout;
> >  };
> >  
> >  #define vin_to_source(vin)		((vin)->parallel.subdev)
> > -- 
> > 2.7.4
> > 
> 
> -- 
> Kind Regards,
> Niklas Söderlund

-- 
Best Regards,
Michael

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