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SubjectRe: [PATCH v3 1/2] media: imx: csi: Disable SMFC before disabling IDMA channel
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Date
Hi,

On Fri, 2019-01-18 at 17:04 -0800, Steve Longerbeam wrote:
> Disable the SMFC before disabling the IDMA channel, instead of after,
> in csi_idmac_unsetup().
>
> 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. Stopping
> the video data stream entering the IDMA channel before disabling the
> channel itself appears to be a reliable fix for the hard lockup. That can
> be done either by disabling the SMFC or the CSI before disabling the
> channel. Disabling the SMFC before the channel is the easiest solution,
> so do that.
>
> Fixes: 4a34ec8e470cb ("[media] media: imx: Add CSI subdev driver")
>
> Suggested-by: Peter Seiderer <ps.report@gmx.net>
> Reported-by: Gaël PORTAY <gael.portay@collabora.com>
> Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>

Gaël, could we get a Tested-by: for this as well?

> Cc: stable@vger.kernel.org
> ---
> Changes in v3:
> - switch from disabling the CSI before the channel to disabling the
> SMFC before the channel.
> Changes in v2:
> - restore an empty line
> - Add Fixes: and Cc: stable
> ---
> drivers/staging/media/imx/imx-media-csi.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
> index e18f58f56dfb..8610027eac97 100644
> --- a/drivers/staging/media/imx/imx-media-csi.c
> +++ b/drivers/staging/media/imx/imx-media-csi.c
> @@ -560,8 +560,8 @@ static int csi_idmac_setup_channel(struct csi_priv *priv)
> static void csi_idmac_unsetup(struct csi_priv *priv,
> enum vb2_buffer_state state)
> {
> - ipu_idmac_disable_channel(priv->idmac_ch);
> ipu_smfc_disable(priv->smfc);
> + ipu_idmac_disable_channel(priv->idmac_ch);

Steve, do you have any theory why this helps? It's a bit weird to
disable the SMFC module while the DMA channel is still enabled. I think
this warrants a big comment, given that enable order is SMFC_EN before
IDMAC channel enable.

Also ipu_smfc_disable is refcounted, so if the other CSI is capturing
simultaneously, this change has no effect.

FWIW, I don't see any regressions though.

regards
Philipp

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