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Message-ID: <c3380c97-1b8c-5a68-168e-fc6150701365@postmarketos.org>
Date:   Sun, 8 Oct 2023 23:52:13 +0300
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Subject: Re: [PATCH] drm/panel: Move AUX B116XW03 out of panel-edp back to
 panel-simple
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To:     Doug Anderson <dianders@chromium.org>,
        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,
        Anton Bambura <jenneron@protonmail.com>
References: <20230925150010.1.Iff672233861bcc4cf25a7ad0a81308adc3bda8a4@changeid>
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From:   Anton Bambura <jenneron@postmarketos.org>
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On 10/5/23 21:10, Doug Anderson wrote:
> Hi,
>
> On Tue, Sep 26, 2023 at 7:01 AM Doug Anderson <dianders@chromium.org> wrote:
>> Hi,
>>
>> On Tue, Sep 26, 2023 at 1:06 AM 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-simple")
>>>> 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 kernel
>>> that doesn't contain commit 474c162878ba ("arm64: dts: mt8183: jacuzzi: Move
>>> 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?
> 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>
>
> In any case, it sounds as if things are working well enough on older
> OSes, so maybe we can just skip trying to do any stable backport on
> this. It still seems like we should land it, though, since the current
> state of the world seems pretty broken. Anyone willing to give a
> Reviewed-by or Acked-by tag?
>
> -Doug
>
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