linux-kernel - Re: [PATCH v3 1/2] drm/bridge: analogix_dp: Grab runtime PM reference for DP-AUX

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Date:   Tue, 22 Feb 2022 14:10:04 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Sean Paul <sean@...rly.run>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        "# 4.0+" <stable@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [PATCH v3 1/2] drm/bridge: analogix_dp: Grab runtime PM reference
 for DP-AUX

Hi,

On Thu, Feb 17, 2022 at 2:42 PM Brian Norris <briannorris@...omium.org> 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 a runtime PM reference, and check that we "see" the panel.
> Don't force any panel power-up, etc., because that can be intrusive, and
> that's not what other drivers do (see
> drivers/gpu/drm/bridge/ti-sn65dsi86.c and
> drivers/gpu/drm/bridge/parade-ps8640.c.)
>
> 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>
> ---
>
> Changes in v3:
> - Avoid panel power-up; just check for HPD state, and let the rest
>   happen "as-is" (e.g., time out, if the caller hasn't prepared things
>   properly)
>
> Changes in v2:
> - Fix spelling in Subject
> - DRM_DEV_ERROR() -> drm_err()
> - Propagate errors from un-analogix_dp_prepare_panel()
>
>  drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Douglas Anderson <dianders@...omium.org>


-Doug