Re: [PATCH] rcar-csi2: restart CSI-2 link if error is detected

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hello Niklas,

On Tue, Mar 12, 2019 at 07:58:13PM +0100, Niklas Söderlund wrote:
> On 2019-03-11 11:53:01 +0100, Hans Verkuil wrote:
> > On 2/18/19 11:15 AM, Niklas Söderlund wrote:
> >> Restart the CSI-2 link if the CSI-2 receiver detects an error during
> >> reception. The driver did nothing when a link error happened and the
> >> data flow simply stopped without the user knowing why.
> >> 
> >> Change the driver to try and recover from errors by restarting the link
> >> and informing the user that something is not right. For obvious reasons
> >> it's not possible to recover from all errors (video source disconnected
> >> for example) but in such cases the user is at least informed of the
> >> error and the same behavior of the stopped data flow is retained.

What error causes have you noticed in practice that would benefit from
this ?

> > What you really would like to have is that when a CSI error is detected,
> > the CSI driver can ask upstream whether or not a disconnect has taken place.
> > 
> > If that was the case, then there is no point in restarting the CSI.
> > 
> > While a disconnect is very uncommon for a sensor, it is of course perfectly
> > normal if an HDMI-to-CSI bridge was connected to the CSI port.

Note that this may not always result in a CSI-2 error, the HDMI to CSI-2
bridge may continue sending valid timings with dummy (or random) data.

> > Unfortunately, we don't have such functionality, but perhaps this is something
> > to think about?
> 
> I think your idea sounds good and that such a functionality could be 
> useful. I have a  feeling such a functionality could be related to 
> notifications?
> 
> > This does mean, however, that I don't like the dev_err since it doesn't have
> > to be an error. I would suggest replacing the first dev_err by dev_info and
> > the second by dev_warn.
> 
> With the background you provides I agree that they should not be 
> dev_err. I will update as you suggest for the next version, thanks.
> 
> >> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> >> ---
> >>  drivers/media/platform/rcar-vin/rcar-csi2.c | 52 ++++++++++++++++++++-
> >>  1 file changed, 51 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
> >> index f90b380478775015..0506fe4106d5c012 100644
> >> --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> >> +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> >> @@ -84,6 +84,9 @@ struct rcar_csi2;
> >>  
> >>  /* Interrupt Enable */
> >>  #define INTEN_REG			0x30
> >> +#define INTEN_INT_AFIFO_OF		BIT(27)
> >> +#define INTEN_INT_ERRSOTHS		BIT(4)
> >> +#define INTEN_INT_ERRSOTSYNCHS		BIT(3)
> >>  
> >>  /* Interrupt Source Mask */
> >>  #define INTCLOSE_REG			0x34
> >> @@ -540,6 +543,10 @@ static int rcsi2_start_receiver(struct rcar_csi2 *priv)
> >>  	if (mbps < 0)
> >>  		return mbps;
> >>  
> >> +	/* Enable interrupts. */
> >> +	rcsi2_write(priv, INTEN_REG, INTEN_INT_AFIFO_OF | INTEN_INT_ERRSOTHS
> >> +		    | INTEN_INT_ERRSOTSYNCHS);
> >> +
> >>  	/* Init */
> >>  	rcsi2_write(priv, TREF_REG, TREF_TREF);
> >>  	rcsi2_write(priv, PHTC_REG, 0);
> >> @@ -702,6 +709,43 @@ static const struct v4l2_subdev_ops rcar_csi2_subdev_ops = {
> >>  	.pad	= &rcar_csi2_pad_ops,
> >>  };
> >>  
> >> +static irqreturn_t rcsi2_irq(int irq, void *data)
> >> +{
> >> +	struct rcar_csi2 *priv = data;
> >> +	u32 status, err_status;
> >> +
> >> +	status = rcsi2_read(priv, INTSTATE_REG);
> >> +	err_status = rcsi2_read(priv, INTERRSTATE_REG);
> >> +
> >> +	if (!status)
> >> +		return IRQ_HANDLED;
> >> +
> >> +	rcsi2_write(priv, INTSTATE_REG, status);
> >> +
> >> +	if (!err_status)
> >> +		return IRQ_HANDLED;
> >> +
> >> +	rcsi2_write(priv, INTERRSTATE_REG, err_status);
> >> +
> >> +	dev_err(priv->dev, "Transfer error, restarting CSI-2 receiver\n");
> >> +
> >> +	return IRQ_WAKE_THREAD;
> >> +}
> >> +
> >> +static irqreturn_t rcsi2_irq_thread(int irq, void *data)
> >> +{
> >> +	struct rcar_csi2 *priv = data;
> >> +
> >> +	mutex_lock(&priv->lock);
> >> +	rcsi2_stop(priv);
> >> +	usleep_range(1000, 2000);
> >> +	if (rcsi2_start(priv))
> >> +		dev_err(priv->dev, "Failed to restart CSI-2 receiver\n");
> >> +	mutex_unlock(&priv->lock);
> >> +
> >> +	return IRQ_HANDLED;
> >> +}
> >> +
> >>  /* -----------------------------------------------------------------------------
> >>   * Async handling and registration of subdevices and links.
> >>   */
> >> @@ -982,7 +1026,7 @@ static int rcsi2_probe_resources(struct rcar_csi2 *priv,
> >>  				 struct platform_device *pdev)
> >>  {
> >>  	struct resource *res;
> >> -	int irq;
> >> +	int irq, ret;
> >>  
> >>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >>  	priv->base = devm_ioremap_resource(&pdev->dev, res);
> >> @@ -993,6 +1037,12 @@ static int rcsi2_probe_resources(struct rcar_csi2 *priv,
> >>  	if (irq < 0)
> >>  		return irq;
> >>  
> >> +	ret = devm_request_threaded_irq(&pdev->dev, irq, rcsi2_irq,
> >> +					rcsi2_irq_thread, IRQF_SHARED,
> >> +					KBUILD_MODNAME, priv);
> >> +	if (ret)
> >> +		return ret;
> >> +
> >>  	priv->rstc = devm_reset_control_get(&pdev->dev, NULL);
> >>  	if (IS_ERR(priv->rstc))
> >>  		return PTR_ERR(priv->rstc);

-- 
Regards,

Laurent Pinchart