MT8183: Only maximum resolution 1280x720?

[Pin-yen Lin]

Hi CK and Paul,

On Mon, Aug 18, 2025 at 12:39 PM Chun-Kuang Hu <chunkuang.hu at kernel.org> wrote:
>
> Paul Menzel <pmenzel at molgen.mpg.de> 於 2025年5月25日 週日 下午2:01寫道：
> >
> > Dear Linux folks,
> >
> >
> > On the older MT8183 device Lenovo IdeaPad Duet Chromebook, running
> > ChromeOS with their Linux 5.10.x, connecting a 1920x1080 Dell monitor to
> > a USB-C adapter using HDMI, only the resolution of 1280x720 is
> > configured, although the adapter also support 1920x1080. It happens with
> > all adapters, for example, LMP USB-C mini Dock [1].
> >
> > I reported it to the Chromium OS issue tracker [1], and the last comment is:
> >
> > > It seems the display pipeline for the internal display (DSI) has
> > > higher clock rate. Also, the resolution support depends on the
> > > refresh rate as well, so the claimed 2400x1080 might only work on
> > > lower refresh rate.
> > >
> > > For the external display, the display modes are mostly rejected by
> > > the pre-defined max_clock_khz in mtk_dpi.c:
> > > https://elixir.bootlin.com/linux/v6.11.4/source/drivers/gpu/drm/mediatek/mtk_dpi.c#L940
> >
> > Can you confirm this? The font rendering seems not so good in the lower
> > resolution, and strangely, playing movies these seem to be rendered in
> > higher resolution (or the monitor or hardware does a good job in
> > up-scaling).
>
> 8183 max_clock_khz is defined in patch [3] by Rex, but this is a
> prepare patch for mt8192 [4].
> I'm not sure that Rex has test it for mt8183.
> Maybe you could try to enlarge 8183 max_clock_khz and see.

I found the internal discussion about this (back in 2018), and the
owner had confirmed MT8183 DPI only supports up to 100Mhz. They also
clearly stated that 1080p at 60 is not supported by MT8183.
>
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/mediatek/mtk_dpi.c?h=v6.17-rc1&id=44b07120291c4b7a6722ccb7149f6b9d938cf5a2
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/mediatek/mtk_dpi.c?h=v6.17-rc1&id=38eaef2dca4ec8dfb9ea84d9dde0f76da5c8caaa
>
> Regards,
> CK
>
> >
> >
> > Kind regards,
> >
> > Paul
> >
> >
> > [1]: https://lmp-adapter.com/product/lmp-usb-c-mini-dock/
> > [2]: https://issuetracker.google.com/issues/295666708

Regards,
Pin-yen