linux-kernel - Re: [PATCH v2 0/6] Pinephone video out fixes (flipping between two frames)

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Date: Mon, 26 Feb 2024 21:07:55 +0100
From: Erico Nunes <nunes.erico@...il.com>
To: Jernej Škrabec <jernej.skrabec@...il.com>
Cc: Ondřej Jirman <megi@....cz>, 
	Maxime Ripard <mripard@...nel.org>, Frank Oltmanns <frank@...manns.dev>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
	Samuel Holland <samuel@...lland.org>, Guido Günther <agx@...xcpu.org>, 
	Purism Kernel Team <kernel@...i.sm>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 0/6] Pinephone video out fixes (flipping between two frames)

Hello,

On Mon, Feb 26, 2024 at 6:29 PM Jernej Škrabec <jernej.skrabec@...il.com> wrote:
>
> Dne ponedeljek, 26. februar 2024 ob 08:13:42 CET je Frank Oltmanns napisal(a):
> > It seems to me that all options for changing the GPU's rate in a stable
> > manner have been exhausted. There seems to be no common interpretation
> > what the phrase "Clock output of PLL_GPU can be used for GPU;and dynamic
> > frequency scaling is not supported" in the Allwinner A64 manual (chapter
> > 3.3.3) means.
> >
> > The BSP uses a fixed rate of 432 MHz. Unless one of you has a clever
> > idea, I suggest to remove the OPPs from the device tree and set the GPU
> > to 432 MHz.
> >
> > What are your thoughts on that?
>
> I can't find original source of these points. So I'm good with removing
> them. But instead of fully removing table, you can just leave one point and
> it should work.

I had posted in
https://gitlab.freedesktop.org/mesa/mesa/-/issues/8410#note_2216628
that I also noticed the A64 datasheet specifically claims that except
for PLL_CPUX and PLL_DDR1, other PLLs don't support frequency scaling.
I was never able to find any evidence that it is actually supposed to
work anyway (perhaps it was hope?). Since you also looked in the BSP
and there is still no evidence that it is supported, I support that we
should likely just remove the OPPs.

Also, I wanted to point out that my series
https://patchwork.freedesktop.org/series/128856/#rev2 was merged to
lima recently. That was the root cause of the "flipping between two
frames" issue that people most probably hit. I highly recommend that
people using the Pinephone update their kernel to include those fixes
to fix that issue. As you mentioned about that symptom here, I just
wanted to point out that it wouldn't be possible to fix the "flipping
frames" issue with just fixes to A64 clock, it does need lima driver
fixes.

Thanks

Erico