Re: [PATCH] drm/msm/dsi: add protection against NULL dsi device

[Sean Paul <sean@poorly.run>]

On Wed, Mar 06, 2019 at 05:28:54PM -0800, Abhinav Kumar wrote:
> When panel probe happens after DSI probe, the DSI probe
> is deferred as per current design. In the probe defer path
> dsi device is destroyed. This NULL dsi device could be
> deferenced by the panel probe in the mipi_dsi_attach path.
> 
> Check for NULL dsi device before accessing it.

It would be really nice to sort all of this out in a manner that's not
sprinkling NULL checks around the driver. I spent 5 minutes looking around and
couldn't really make sense of how all of these pieces interact, but this seems
like it might be an architectural problem (perhaps since dpu was using its own
panel stuff instead of drm_panel?).

Anyways, it'd be nice to fix that.

In the meantime, could you please add a big comment like the !dev check in this
function explaining how this situation can come to pass? That way the knowledge
isn't lost and whoever comes along to clean up all of these probe checks will
have some clue as to what's going on.

Sean

> 
> Reported-by: Jeffrey Hugo <jhugo@codeaurora.org>
> Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
> Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_manager.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 80aa634..cc2569d 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -769,7 +769,7 @@ bool msm_dsi_manager_cmd_xfer_trigger(int id, u32 dma_base, u32 len)
>  void msm_dsi_manager_attach_dsi_device(int id, u32 device_flags)
>  {
>  	struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
> -	struct drm_device *dev = msm_dsi->dev;
> +	struct drm_device *dev = msm_dsi ? msm_dsi->dev : NULL;
>  	struct msm_drm_private *priv;
>  	struct msm_kms *kms;
>  	struct drm_encoder *encoder;
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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