linux-kernel - Re: [PATCH] drm/meson: add support for 2560x1440 resolution output

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Message-ID: <CAFBinCB9hxgJt_rqdy_1bM0FjnnCt1K=Au77yxeuWox1wSvdDw@mail.gmail.com>
Date: Sat, 4 Oct 2025 22:22:38 +0200
From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To: Christian Hewitt <christianshewitt@...il.com>, Neil Armstrong <neil.armstrong@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Kevin Hilman <khilman@...libre.com>, Jerome Brunet <jbrunet@...libre.com>, 
	dri-devel@...ts.freedesktop.org, linux-amlogic@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Dongjin Kim <tobetter@...il.com>
Subject: Re: [PATCH] drm/meson: add support for 2560x1440 resolution output

Hi Christian,

On Mon, Sep 29, 2025 at 1:58 AM Christian Hewitt
<christianshewitt@...il.com> wrote:
>
> > On 29 Sep 2025, at 1:24 am, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:
> >
> > Hi Christian,
> >
> > On Sat, Sep 27, 2025 at 3:02 PM Christian Hewitt
> > <christianshewitt@...il.com> wrote:
> > [...]
> >> @@ -894,6 +908,10 @@ static void meson_vclk_set(struct meson_drm *priv,
> >>                        m = 0xf7;
> >>                        frac = vic_alternate_clock ? 0x8148 : 0x10000;
> >>                        break;
> >> +               case 4830000:
> >> +                       m = 0xc9;
> >> +                       frac = 0xd560;
> >> +                       break;
> > Initially I thought this was wrong because it's only added for the
> > G12A (which is also used on G12B and SM1) code-path, leaving out the
> > GX SoCs.
> >
> > Was the 2560x1440 mode tested on a computer monitor or a TV?
> > I suspect it's the former, so I think it expected the code to take the
> > MESON_VCLK_TARGET_DMT path, which automatically calculates m and frac.
> >
> > I'll give it a try on Friday as I do have a computer monitor with that
> > resolution - so any hints for testing are welcome!
>
> The original patch is from Hardkernel sources - I’ve picked it several
> years ago and then updated values semi-recently after 1000ULL changes.
> The user who originally requested that I cherry-pick it (and tested it)
> was using an Odroid N2+ board (G12B) with a Dell monitor IIRC. It’s not
> tested by myself as I only have TV’s not monitors, so it will be good
> to have your confirmation (either way). If it’s wrong I’ll be happy to
> drop it - I’m just trying to upstream and offload some longer-running
> and allegedly good patches in the LibreELEC kernel patchset.
So I've tried it on a Le Potato (S905X SoC) board. This patch doesn't
do anything here (as expected, since it only targets the G12A and
later code-path).

Doing some more analysis, it seems that
meson_venc_hdmi_supported_mode() simply prevents using any mode with
more than 1920 pixels.
I attached a simple patch to overcome this (discarding any
meson_vclk.c changes):
$ cat /sys/class/drm/card1-HDMI-A-1/modes
2560x1440
2048x1152
1920x1200
1920x1080
...

My monitor's OSD tells me that I'm running at 2560x1440@...z.

@Neil, should we bump the limits in meson_venc.c to "4Kx2K@60" (that's
a quote from both, S905/GXBB and S905D3/SM1 datasheets), most likely
meaning: 4096x2160?


Best regards,
Martin

View attachment "meson_venc-hdmi-support-1440p-screen.diff" of type "text/x-patch" (661 bytes)