Date: Thu, 23 May 2024 19:58:00 +0100
From: Måns Rullgård <mans@...sr.com>
To: Frank Oltmanns <frank@...manns.dev>
Cc: Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec
 <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, Guido
 Günther <agx@...xcpu.org>, Purism Kernel Team
 <kernel@...i.sm>, Ondrej
 Jirman <megi@....cz>, Neil Armstrong <neil.armstrong@...aro.org>, Jessica
 Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, 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,
 stable@...r.kernel.org
Subject: Re: [PATCH v4 1/5] clk: sunxi-ng: common: Support minimum and
 maximum rate

Måns Rullgård <mans@...sr.com> writes:

> Frank Oltmanns <frank@...manns.dev> writes:
>
>> Hi Måns,
>>
>> 21.05.2024 15:43:10 Måns Rullgård <mans@...sr.com>:
>>
>>> Frank Oltmanns <frank@...manns.dev> writes:
>>>
>>>> The Allwinner SoC's typically have an upper and lower limit for their
>>>> clocks' rates. Up until now, support for that has been implemented
>>>> separately for each clock type.
>>>>
>>>> Implement that functionality in the sunxi-ng's common part making use of
>>>> the CCF rate liming capabilities, so that it is available for all clock
>>>> types.
>>>>
>>>> Suggested-by: Maxime Ripard <mripard@...nel.org>
>>>> Signed-off-by: Frank Oltmanns <frank@...manns.dev>
>>>> Cc: stable@...r.kernel.org
>>>> ---
>>>> drivers/clk/sunxi-ng/ccu_common.c | 19 +++++++++++++++++++
>>>> drivers/clk/sunxi-ng/ccu_common.h |  3 +++
>>>> 2 files changed, 22 insertions(+)
>>>
>>> This just landed in 6.6 stable, and it broke HDMI output on an A20 based
>>> device, the clocks ending up all wrong as seen in this diff of
>>> /sys/kernel/debug/clk/clk_summary:

[...]

>>> Reverting this commit makes it work again.
>>
>> Thank you for your detailed report!
>>
>> I've had a first look at hdmi-tmds and hdmi-ddc, and neither seems to
>> be calling ccu_is_better_rate() in their determine_rate()
>> functions. Their parents have the exact same rates in your diff, so,
>> my current working assumption is that they can't be the cause either.
>>
>> I'll have a more detailed look over the weekend. Until then, if anyone
>> has some ideas where I should have a look next, please share your
>> thoughts.
>
> In case it's relevant, this system doesn't use the HDMI DDC, the
> physical DDC pins being connected to a different I2C adapter for
> various reasons.
>
> From the clk_summary diff, I see a few things:
>
> 1. hdmi-tmds has changed parent from pll-video1-2x to pll-video0-2x.
> 2. The ratio of hdmi-tmds to its parent has changed from 1/8 to 1.
> 3. The resulting rate bears no relation to the pixel clock from EDID.
>
> I tried kernel 6.9.1 as well, and that doesn't work either.  I'll keep
> digging and try to narrow it down.

It turns out HDMI output is broken in v6.9 for a different reason.
However, this commit (b914ec33b391 clk: sunxi-ng: common: Support
minimum and maximum rate) requires two others as well in order not
to break things on the A20:

cedb7dd193f6 drm/sun4i: hdmi: Convert encoder to atomic
9ca6bc246035 drm/sun4i: hdmi: Move mode_set into enable

With those two (the second depends on the first) cherry-picked on top of
v6.6.31, the HDMI output is working again.  Likewise on v6.8.10.

-- 
Måns Rullgård

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