linux-kernel - Re: [PATCH] drm/panel-simple: Power the panel when probing DP AUX backlight

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Date:   Wed, 14 Jul 2021 14:48:33 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Rajeev Nandan <rajeevny@...eaurora.org>,
        Robert Foss <robert.foss@...aro.org>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        Sam Ravnborg <sam@...nborg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel-simple: Power the panel when probing DP AUX
 backlight

Reviewed-by: Lyude Paul <lyude@...hat.com>

On Wed, 2021-07-14 at 09:33 -0700, Douglas Anderson wrote:
> When I tried booting up a device that needed the DP AUX backlight, I
> found an error in the logs:
>   panel-simple-dp-aux: probe of aux-ti_sn65dsi86.aux.0 failed with error -
> 110
> 
> The aux transfers were failing because the panel wasn't powered. Just
> like when reading the EDID we need to power the panel when trying to
> talk to it. Add the needed pm_runtime calls.
> 
> After I do this I can successfully probe the panel and adjust the
> backlight on my board.
> 
> Fixes: bfd451403d70 ("drm/panel-simple: Support DP AUX backlight")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  drivers/gpu/drm/panel/panel-simple.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c
> b/drivers/gpu/drm/panel/panel-simple.c
> index e0a05f366ce6..9b286bd4444f 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -827,7 +827,10 @@ static int panel_simple_probe(struct device *dev, const
> struct panel_desc *desc,
>                 goto disable_pm_runtime;
>  
>         if (!panel->base.backlight && panel->aux) {
> +               pm_runtime_get_sync(dev);
>                 err = drm_panel_dp_aux_backlight(&panel->base, panel->aux);
> +               pm_runtime_mark_last_busy(dev);
> +               pm_runtime_put_autosuspend(dev);
>                 if (err)
>                         goto disable_pm_runtime;
>         }

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat