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From:   Doug Anderson <dianders@chromium.org>
Date:   Thu, 18 Aug 2022 08:03:24 -0700
Message-ID: <CAD=FV=UXFiA4hW8_cmO0Di-NCpqvkjTqqOfbc6DfD5Rs8aT6hA@mail.gmail.com>
Subject: Re: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to
 power-on sequence
To:     Hsin-Yi Wang <hsinyi@chromium.org>
Cc:     Rock Chiu <rock.chiu@paradetech.corp-partner.google.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
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Hi,

On Wed, Aug 17, 2022 at 8:22 PM Hsin-Yi Wang <hsinyi@chromium.org> wrote:
>
> On Thu, Aug 18, 2022 at 11:19 AM Rock Chiu
> <rock.chiu@paradetech.corp-partner.google.com> wrote:
> >
> > How does T4/T5  impact the real case? We talked previously the T4/T5
> > shouldn't cause user impact.
> > Do we have testing data from ODM?
> >
> Please leave comments below the previous comment's headline.
>
> I'm confused. The reason I upstreamed this patch is because this is in
> your application note and you asked us to help upstream it. Now do you
> mean that we don't need T4 and T5?

I think Rock is asking what problems the extra delay is causing. In
other words: why do we care about keeping these delays short?

The answer is that it affects boot speed and also resume speed of
devices. Adding these two delays here means that there's an extra 100
ms before the user can see something on the screen. That may not seem
like a lot, but those kinds of delays add up quickly. At least on
Chromebooks, booting quickly is always a big goal.

-Doug