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From:   Doug Anderson <dianders@chromium.org>
Date:   Thu, 12 Oct 2023 09:45:09 -0700
Message-ID: <CAD=FV=WAYYv5h6oWWhEJHyZesE5cguBqVufCmK6s4gvMeNkCWg@mail.gmail.com>
Subject: Re: [PATCH] drm/panel: Move AUX B116XW03 out of panel-edp back to panel-simple
To:     Anton Bambura <jenneron@postmarketos.org>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kernel.org,
        Hsin-Yi Wang <hsinyi@chromium.org>, matthias.bgg@gmail.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-mediatek@lists.infradead.org,
        Marek Szyprowski <m.szyprowski@samsung.com>, airlied@gmail.com,
        daniel@ffwll.ch, jitao.shi@mediatek.com, linus.walleij@linaro.org,
        linux-kernel@vger.kernel.org, neil.armstrong@linaro.org,
        quic_jesszhan@quicinc.com, sam@ravnborg.org,
        Anton Bambura <jenneron@protonmail.com>
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Hi,

On Sun, Oct 8, 2023 at 1:52=E2=80=AFPM Anton Bambura <jenneron@postmarketos=
.org> wrote:
>
>
> On 10/5/23 21:10, Doug Anderson wrote:
> > Hi,
> >
> > On Tue, Sep 26, 2023 at 7:01=E2=80=AFAM Doug Anderson <dianders@chromiu=
m.org> wrote:
> >> Hi,
> >>
> >> On Tue, Sep 26, 2023 at 1:06=E2=80=AFAM AngeloGioacchino Del Regno
> >> <angelogioacchino.delregno@collabora.com> wrote:
> >>> Il 26/09/23 00:00, Douglas Anderson ha scritto:
> >>>> In commit 5f04e7ce392d ("drm/panel-edp: Split eDP panels out of
> >>>> panel-simple") I moved a pile of panels out of panel-simple driver
> >>>> into the newly created panel-edp driver. One of those panels, howeve=
r,
> >>>> shouldn't have been moved.
> >>>>
> >>>> As is clear from commit e35e305eff0f ("drm/panel: simple: Add AUO
> >>>> B116XW03 panel support"), AUX B116XW03 is an LVDS panel. It's used i=
n
> >>>> exynos5250-snow and exynos5420-peach-pit where it's clear that the
> >>>> panel is hooked up with LVDS. Furthermore, searching for datasheets =
I
> >>>> found one that makes it clear that this panel is LVDS.
> >>>>
> >>>> As far as I can tell, I got confused because in commit 88d3457ceb82
> >>>> ("drm/panel: auo,b116xw03: fix flash backlight when power on") Jitao
> >>>> Shi added "DRM_MODE_CONNECTOR_eDP". That seems wrong. Looking at the
> >>>> downstream ChromeOS trees, it seems like some Mediatek boards are
> >>>> using a panel that they call "auo,b116xw03" that's an eDP panel. The
> >>>> best I can guess is that they actually have a different panel that h=
as
> >>>> similar timing. If so then the proper panel should be used or they
> >>>> should switch to the generic "edp-panel" compatible.
> >>>>
> >>>> When moving this back to panel-edp, I wasn't sure what to use for
> >>>> .bus_flags and .bus_format and whether to add the extra "enable" del=
ay
> >>>> from commit 88d3457ceb82 ("drm/panel: auo,b116xw03: fix flash
> >>>> backlight when power on"). I've added formats/flags/delays based on =
my
> >>>> (inexpert) analysis of the datasheet. These are untested.
> >>>>
> >>>> NOTE: if/when this is backported to stable, we might run into some
> >>>> trouble. Specifically, before 474c162878ba ("arm64: dts: mt8183:
> >>>> jacuzzi: Move panel under aux-bus") this panel was used by
> >>>> "mt8183-kukui-jacuzzi", which assumed it was an eDP panel. I don't
> >>>> know what to suggest for that other than someone making up a bogus
> >>>> panel for jacuzzi that's just for the stable channel.
> >>>>
> >>>> Fixes: 88d3457ceb82 ("drm/panel: auo,b116xw03: fix flash backlight w=
hen power on")
> >>>> Fixes: 5f04e7ce392d ("drm/panel-edp: Split eDP panels out of panel-s=
imple")
> >>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> >>>> ---
> >>>> I haven't had a snow or peach-pit hooked up for debugging / testing
> >>>> for years. I presume that they must be broken and hope that this fix=
es
> >>>> them.
> >>> We could avoid backport breakages by avoiding to backport this to any=
 kernel
> >>> that doesn't contain commit 474c162878ba ("arm64: dts: mt8183: jacuzz=
i: Move
> >>> panel under aux-bus")... because creating a dummy panel to get two wr=
ongs
> >>> right is definitely not ok.
> >> Sure, except that leaves us with ... a breakage. :-P
> >>
> >> Although I haven't tested it, I have a hard time believing that
> >> exynos5250-snow and exynos5420-peach-pit will work properly with the
> >> panel defined as an eDP panel. That means that they will be broken. If
> >> someone cared to get those fixed in a stable backport then we'd be
> >> stuck deciding who to break. If you have any brilliant ideas then I'm
> >> all ears.
> >>
> >> ...then again, I presume this has been broken since commit
> >> 88d3457ceb82 ("drm/panel: auo,b116xw03: fix flash backlight when power
> >> on"). That was a little over 3 years ago. Maybe I'm wrong and somehow
> >> things still limp along and sorta work even though the panel is
> >> defined incorrectly?
> > I dug out a exynos5250-snow out of my pile and booted postmarket OS on
> > it, which was shockingly easy/pleasant (kudos to those involved!). I
> > found that it was booting a kernel based on 6.1.24. Digging into
> > sysfs, I found that indeed it appeared to be using the "panel-edp"
> > driver, so I guess it is limping along with the wrong driver and wrong
> > flags...
> >
> > It wasn't totally clear for me how to build a new kernel and deploy it
> > for postmarket OS, so I wasn't able to confirm this change. I've CCed
> > the person listed on the postmarket OS wiki though to see if they have
> > any insight.
> Tested it on peach-pit using linux-next with this patch applied. Panel
> still works and "dmesg | grep panel" returns panel_simple instead of
> panel_edp.
>
> Tested-by: Anton Bambura <jenneron@postmarketos.org>

Pushed to drm-misc-fixes:

ad3e33fe071d drm/panel: Move AUX B116XW03 out of panel-edp back to panel-si=
mple

-Doug