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From:   Doug Anderson <dianders@chromium.org>
Date:   Tue, 26 Sep 2023 07:01:55 -0700
Message-ID: <CAD=FV=UWQgLLfU4X+6OUR5AWOkJKwG9J7BbKGRCgze6LTY6JNw@mail.gmail.com>
Subject: Re: [PATCH] drm/panel: Move AUX B116XW03 out of panel-edp back to panel-simple
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     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
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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, however,
> > 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 in
> > 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 has
> > 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" delay
> > 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 when=
 power on")
> > Fixes: 5f04e7ce392d ("drm/panel-edp: Split eDP panels out of panel-simp=
le")
> > 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 fixes
> > them.
>
> We could avoid backport breakages by avoiding to backport this to any ker=
nel
> that doesn't contain commit 474c162878ba ("arm64: dts: mt8183: jacuzzi: M=
ove
> panel under aux-bus")... because creating a dummy panel to get two wrongs
> 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?

-Doug