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

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Message-ID: <20211001203722.GZ2515@art_vandelay>
Date:   Fri, 1 Oct 2021 16:37:22 -0400
From:   Sean Paul <sean@...rly.run>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        linux-kernel@...r.kernel.org, Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        stable@...r.kernel.org, Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [PATCH] drm/brdige: analogix_dp: Grab runtime PM reference for
 DP-AUX

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@...r.kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> Signed-off-by: Brian Norris <briannorris@...omium.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