linux-kernel - Re: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to power-on sequence

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Date:   Mon, 22 Aug 2022 09:33:00 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Rock Chiu <rock.chiu@...adetech.corp-partner.google.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to
 power-on sequence

Hi,

On Thu, Aug 18, 2022 at 8:03 AM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Wed, Aug 17, 2022 at 8:22 PM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
> >
> > On Thu, Aug 18, 2022 at 11:19 AM Rock Chiu
> > <rock.chiu@...adetech.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.

While I'm not very happy with this change and I don't really
understand why these delays need to be so long, if folks are really
certain that we need them and can't make them shorter then I guess we
can land it. I'll wait a few more days in case anyone wants to chime
in with their thoughts.

-Doug