Re: [PATCH v2 1/2] media: imx: csi: Disable CSI immediately after last EOF

[Philipp Zabel <p.zabel@pengutronix.de>]

On Thu, 2019-01-17 at 12:49 -0800, Steve Longerbeam wrote:
> Disable the CSI immediately after receiving the last EOF before stream
> off (and thus before disabling the IDMA channel).
> 
> This fixes a complete system hard lockup on the SabreAuto when streaming
> from the ADV7180, by repeatedly sending a stream off immediately followed
> by stream on:
> 
> while true; do v4l2-ctl  -d4 --stream-mmap --stream-count=3; done
> 
> Eventually this either causes the system lockup or EOF timeouts at all
> subsequent stream on, until a system reset.
> 
> The lockup occurs when disabling the IDMA channel at stream off. Disabling
> the CSI before disabling the IDMA channel appears to be a reliable fix for
> the hard lockup.
>
> Fixes: 4a34ec8e470cb ("[media] media: imx: Add CSI subdev driver")
> 
> Reported-by: Gaël PORTAY <gael.portay@collabora.com>
> Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
> Cc: stable@vger.kernel.org
> ---
> Changes in v2:
> - restore an empty line
> - Add Fixes: and Cc: stable
> ---
>  drivers/staging/media/imx/imx-media-csi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
> index e18f58f56dfb..e0f6f88e2e70 100644
> --- a/drivers/staging/media/imx/imx-media-csi.c
> +++ b/drivers/staging/media/imx/imx-media-csi.c
> @@ -681,6 +681,8 @@ static void csi_idmac_stop(struct csi_priv *priv)
>  	if (ret == 0)
>  		v4l2_warn(&priv->sd, "wait last EOF timeout\n");
>  
> +	ipu_csi_disable(priv->csi);
> +

Can you add a short comment why this call is here? Since now
csi_idmac_stop is kind of a misnomer and symmetry with csi(_idmac)_start
is broken, I think this is a bit un-obvious.

Also note that now the error path of csi_start() will now call
ipu_csi_disable() while the CSI is disabled. This happens to work
because that just calls ipu_module_disable(), which is not refcounted.

>  	devm_free_irq(priv->dev, priv->eof_irq, priv);
>  	devm_free_irq(priv->dev, priv->nfb4eof_irq, priv);
>  
> @@ -793,9 +795,9 @@ static void csi_stop(struct csi_priv *priv)
>  		/* stop the frame interval monitor */
>  		if (priv->fim)
>  			imx_media_fim_set_stream(priv->fim, NULL, false);
> +	} else {
> +		ipu_csi_disable(priv->csi);
>  	}
> -
> -	ipu_csi_disable(priv->csi);

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

regards
Philipp