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

[Chen-Yu Tsai]

On Wed, Aug 30, 2023 at 7:11 PM Michael Walle <mwalle at kernel.org> wrote:
>
> >> 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.

This is probably because support for this SoC began with Chromebooks,
which have fixed and defined uses for the pipelines. I suspect that
what you are working on is much more flexible.

The driver should be made to allow dynamic selection of outputs, as
is commonly seen with other drivers, but I don't know if that's on
anyone's TODO list.

ChenYu

> > 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