linux-kernel - Re: [PATCH v3 1/2] media: imx: csi: Disable SMFC before disabling IDMA channel

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Message-ID: <1548071350.3287.3.camel@pengutronix.de>
Date:   Mon, 21 Jan 2019 12:49:10 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Steve Longerbeam <slongerbeam@...il.com>,
        linux-media@...r.kernel.org
Cc:     Gael PORTAY <gael.portay@...labora.com>,
        Peter Seiderer <ps.report@....net>, stable@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] media: imx: csi: Disable SMFC before disabling
 IDMA channel

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@....net>
> Reported-by: Gaël PORTAY <gael.portay@...labora.com>
> Signed-off-by: Steve Longerbeam <slongerbeam@...il.com>

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

> Cc: stable@...r.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