linux-kernel - Re: [PATCH v2 0/4] drm/bridge: ti-sn65dsi86: Support EDID reading

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Message-ID: <CAD=FV=V3kktCrwvMBeOy1dnQGYuV-ZUGX81+upRZacfzxjceFg@mail.gmail.com>
Date:   Mon, 2 Nov 2020 08:37:21 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonas Karlman <jonas@...boo.se>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Sean Paul <seanpaul@...omium.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Vinod Koul <vkoul@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH v2 0/4] drm/bridge: ti-sn65dsi86: Support EDID reading

Hi,

On Sun, Nov 1, 2020 at 9:37 AM Sam Ravnborg <sam@...nborg.org> wrote:
>
> Hi Stephen.
>
> On Thu, Oct 29, 2020 at 06:17:34PM -0700, Stephen Boyd wrote:
> > This patch series cleans up the DDC code a little bit so that
> > it is more efficient time wise and supports grabbing the EDID
> > of the eDP panel over the aux channel. I timed this on a board
> > I have on my desk and it takes about 20ms to grab the EDID out
> > of the panel and make sure it is valid.
> >
> > The first two patches seem less controversial so I stuck them at
> > the beginning. The third patch does the EDID reading and caches
> > it so we don't have to keep grabbing it over and over again. And
> > finally the last patch updates the reply field so that short
> > reads and nacks over the channel are reflected properly instead of
> > treating them as some sort of error that can't be discerned.
> >
> > Stephen Boyd (4):
> >   drm/bridge: ti-sn65dsi86: Combine register accesses in
> >     ti_sn_aux_transfer()
> >   drm/bridge: ti-sn65dsi86: Make polling a busy loop
> >   drm/bridge: ti-sn65dsi86: Read EDID blob over DDC
> >   drm/bridge: ti-sn65dsi86: Update reply on aux failures
>
> Series looks good. You can add my a-b on the full series.
> Acked-by: Sam Ravnborg <sam@...nborg.org>
>
> I can apply after Douglas have had a look at the patches he did not r-b
> yet.

They look fine to me now assuming that Stepehn has tested patch #1
enough that we're confident that the slight change in ordering isn't
going to mess anything up.  Laurent also had comments about caching
the EDID on patch #3.  If he feels strongly about getting rid of that,
it'll need another spin and we'll just have to suck up the small boot
time penalty until we can find a solution in the core.


> Any chance we can convince you to prepare this bridge driver for use in
> a chained bridge setup where the connector is created by the display
> driver and uses drm_bridge_funcs?
>
> First step wuld be to introduce the use of a panel_bridge.
> Then add get_edid to drm_bridge_funcs and maybe more helpers.
>
> Then natural final step would be to move connector creation to the
> display driver - see how other uses drm_bridge_connector_init() to do so
> - it is relatively simple.
>
> Should be doable - and reach out if you need some help.

At some point I think Vinod tried to prepare a patch for this and I
tried it, but it didn't just work.  I spent an hour or so poking at it
and I couldn't quite figure out why and I couldn't find enough other
examples to compare against to see what was wrong...  That was a few
months ago, though.  Maybe things are in a better shape now?

-Doug