linux-kernel - Re: [PATCH v7 09/11] drm/mediatek: dp: Add support for embedded DisplayPort aux-bus

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Date:   Wed, 30 Aug 2023 13:11:35 +0200
From:   Michael Walle <mwalle@...nel.org>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     angelogioacchino.delregno@...labora.com, airlied@...il.com,
        amergnat@...libre.com, chunkuang.hu@...nel.org, ck.hu@...iatek.com,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        ehristev@...labora.com, kernel@...labora.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, matthias.bgg@...il.com,
        p.zabel@...gutronix.de, wenst@...omium.org
Subject: Re: [PATCH v7 09/11] drm/mediatek: dp: Add support for embedded
 DisplayPort aux-bus

>> While digging through the code I realized that all the outputs and 
>> pipelines
>> are harcoded. Doh. For all the mediatek SoCs. Looks like major 
>> restriction
>> to
>> me. E.g. there is also DSI and HDMI output on the mt8195. I looked at 
>> the
>> downstream linux and there, the output is not part of the pipeline. 
>> Are you
>> aware of any work in that direction?
> 
> I'm not sure I get what output and pipelines are hardcoded that you're 
> referring
> to (besides the one in the mtk-dsi/dpi driver that you already sent the 
> patch
> fixing).

Have a look at [1]. That main path ends with the DP_INTF0 which is the
eDP output. But from what I understand that path can also use the DSI
output. But that is a pattern for all the paths in that file. Looks like
all supported boards in the kernel will have the output type for a given
SoC/path (or maybe the mt8195 is the first one which supports different
output interfaces).

If you have a look at the mediatek kernel instead [2], there the last
part of the path is not fixed, but there is also a .conn_routes property
by which you seem to be able to choose the actual output interface.

I was just curious if you know of any development for that (or similar)
in the kernel.

-michael

> And I'm not familiar with the DSI and HDMI output support on MT8195, so 
> I can't
> help with that.
> 
> Thanks,
> Nícolas

[1] 
https://elixir.bootlin.com/linux/v6.5/source/drivers/gpu/drm/mediatek/mtk_drm_drv.c#L210
[2] 
https://gitlab.com/mediatek/aiot/bsp/linux/-/blob/mtk-v5.15-dev/drivers/gpu/drm/mediatek/mtk_drm_drv.c?ref_type=heads#L425