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

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Message-ID: <CAAOTY_8vLqU30L3+ijYJPLrioRsUwVwJAeumtVYfRJ9e5tjp4A@mail.gmail.com>
Date: Thu, 14 Aug 2025 22:35:41 +0800
From: Chun-Kuang Hu <chunkuang.hu@...nel.org>
To: Paul Menzel <pmenzel@...gen.mpg.de>
Cc: Chun-Kuang Hu <chunkuang.hu@...nel.org>, 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?

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.

[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