linux-kernel - Re: [PATCH 2/2] drm/bridge: it6505: Drop EDID cache on bridge power off

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Message-ID: <CAD=FV=X2V+LQ1XOo_eJ1Vv3Pn+E309kvyY9FOzaZP_j8ToXM2g@mail.gmail.com>
Date: Tue, 24 Sep 2024 10:48:37 -0700
From: Doug Anderson <dianders@...omium.org>
To: Pin-yen Lin <treapking@...omium.org>
Cc: Xin Ji <xji@...logixsemi.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, linux-kernel@...r.kernel.org, 
	Sam Ravnborg <sam@...nborg.org>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 2/2] drm/bridge: it6505: Drop EDID cache on bridge power off

Hi,

On Mon, Sep 23, 2024 at 8:53 PM Pin-yen Lin <treapking@...omium.org> wrote:
>
> The bridge might miss the display change events when it's powered off.
> This happens when a user changes the external monitor when the system
> is suspended and the embedded controller doesn't not wake AP up.
>
> It's also observed that one DP-to-HDMI bridge doesn't work correctly
> when there is no EDID read after it is powered on.
>
> Drop the cache to force an EDID read after system resume to fix this.
>
> Fixes: 11feaef69d0c ("drm/bridge: it6505: Add caching for EDID")
> Signed-off-by: Pin-yen Lin <treapking@...omium.org>

Ah, I guess this answers my question in the previous patch about
whether caching was important even for external displays since this
driver only supports external DP and the commit you mention in "Fixes"
says that caching was important.

So this looks reasonable. One thing I wonder is if you're totally
guaranteed to get a PM Runtime suspend whenever you get an unplug /
replug of a display. I tried to dig a little bit but I'm not super
familiar with this bridge and it looks complicated enough that I guess
I'll have to trust that it's fine. So...

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