Re: [PATCH] drm/brdige: analogix_dp: Grab runtime PM reference for DP-AUX

[Sean Paul <sean@poorly.run>]

On Wed, Sep 29, 2021 at 02:41:03PM -0700, Brian Norris wrote:
> If the display is not enable()d, then we aren't holding a runtime PM
> reference here. Thus, it's easy to accidentally cause a hang, if user
> space is poking around at /dev/drm_dp_aux0 at the "wrong" time.
> 
> Let's get the panel and PM state right before trying to talk AUX.
> 
> Fixes: 0d97ad03f422 ("drm/bridge: analogix_dp: Remove duplicated code")
> Cc: <stable@vger.kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Signed-off-by: Brian Norris <briannorris@chromium.org>
> ---
> 
>  .../gpu/drm/bridge/analogix/analogix_dp_core.c  | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index b7d2e4449cfa..a1b553904b85 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -1632,8 +1632,23 @@ static ssize_t analogix_dpaux_transfer(struct drm_dp_aux *aux,
>  				       struct drm_dp_aux_msg *msg)
>  {
>  	struct analogix_dp_device *dp = to_dp(aux);
> +	int ret, ret2;
>  
> -	return analogix_dp_transfer(dp, msg);
> +	ret = analogix_dp_prepare_panel(dp, true, false);
> +	if (ret) {
> +		DRM_DEV_ERROR(dp->dev, "Failed to prepare panel (%d)\n", ret);

s/DRM_DEV_ERROR/drm_err/

> +		return ret;
> +	}
> +
> +	pm_runtime_get_sync(dp->dev);
> +	ret = analogix_dp_transfer(dp, msg);
> +	pm_runtime_put(dp->dev);
> +
> +	ret2 = analogix_dp_prepare_panel(dp, false, false);
> +	if (ret2)
> +		DRM_DEV_ERROR(dp->dev, "Failed to unprepare panel (%d)\n", ret2);

What's the reasoning for not propagating unprepare failures? I feel like that
should be fair game.

> +
> +	return ret;
>  }
>  
>  struct analogix_dp_device *
> -- 
> 2.33.0.685.g46640cef36-goog
> 

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