linux-kernel - Re: MT8183: Only maximum resolution 1280x720?

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Message-ID: <CAEXTbpd=-mB-n1EVb4Y7RDxkJ86b-HrFWyErgTE_FYoViZRdpw@mail.gmail.com>
Date: Mon, 18 Aug 2025 12:42:21 +0800
From: Pin-yen Lin <treapking@...omium.org>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>, Paul Menzel <pmenzel@...gen.mpg.de>
Cc: Philipp Zabel <p.zabel@...gutronix.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, dri-devel@...ts.freedesktop.org, 
	linux-mediatek@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: MT8183: Only maximum resolution 1280x720?

Hi CK and Paul,

On Mon, Aug 18, 2025 at 12:39 PM Chun-Kuang Hu <chunkuang.hu@...nel.org> wrote:
>
> Paul Menzel <pmenzel@...gen.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@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