linux-kernel - Re: [PATCH] drm/bridge: parade-ps8640: Fix additional suspend/resume at bootup

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Message-ID: <CAD=FV=XWdA5kC5VpRPNWzCQDJjmDg5s7bP=sa7yVuqnRcxWf+w@mail.gmail.com>
Date:   Fri, 12 Nov 2021 08:32:04 -0800
From:   Doug Anderson <dianders@...gle.com>
To:     yangcong <yangcong5@...qin.corp-partner.google.com>
Cc:     swboyd@...omium.org, robert.foss@...aro.org,
        narmstrong@...libre.com, laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, a.hajda@...sung.com, philipchen@...omium.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: parade-ps8640: Fix additional suspend/resume
 at bootup

Hi,

On Fri, Nov 12, 2021 at 12:43 AM yangcong
<yangcong5@...qin.corp-partner.google.com> wrote:
>
> Through log and waveform, we can see that there will be additional
> suspend/resume when booting. This timing does not meet the ps8640 spec.
> It seems that the delay of 500ms does not satisfied drm_panel_get_modes.
> I increased it to 900ms and it seems that this problem can be solved.
> To be safe, I'd just round up to a full 1000.

Do be clear: I'm still not convinced that the old 500 ms actually
causes any real problems. I think someone is just measuring with a
scope and upset that they see the device power on and then power off
again. In any case, if we can avoid an extra power cycle at boot then
that seems sane to me. Since this is a tiny change, I'll plan to merge
it some time next week unless someone yells.

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