linux-kernel - Re: [PATCH v4 1/5] clk: sunxi-ng: common: Support minimum and maximum rate

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Message-ID: <1b359d7e-fe85-48ca-87aa-37ab7e34aaf6@oltmanns.dev>
Date: Wed, 26 Jun 2024 19:07:19 +0200 (GMT+02:00)
From: Frank Oltmanns <frank@...manns.dev>
To: "Pafford, Robert J." <pafford.9@...keyemail.osu.edu>
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

Hi Robert,

26.06.2024 18:03:24 Pafford, Robert J. <pafford.9@...keyemail.osu.edu>:

> Hi Frank,
>
> Moving to a new for loop makes sense. Let me know when you have a patch

The patch is here, strange you didn't receive it:
https://lore.kernel.org/all/20240623-sunxi-ng_fix_common_probe-v1-1-7c97e32824a1@oltmanns.dev/


> and I'll be glad to test it on my board. I do also wonder if this may
> have contributed to some of the HDMI issues seen in the other thread.

My thought's exactly!

Best regards,
  Frank

>
> Best,
> Robert
>
>> Hi Robert,
>>
>> I'm truly sorry for the trouble the patch has caused you and for my late
>> reply!
>>
>> On 2024-06-14 at 23:52:08 +0000, "Pafford, Robert J." <pafford.9@...keyemail.osu.edu> wrote:
>>>> 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 patch appears to cause a buffer under-read bug due to the call to 'hw_to_ccu_common', which assumes all entries
>>> in the desc->hw_clocks->hws array are contained in ccu_common structs.
>>>
>>> However, not all clocks in the array are contained in ccu_common structs. For example, as part
>>> of the "sun20i-d1-ccu" driver, the "pll-video0" clock holds the 'clk_hw' struct inside of a 'clk_fixed_factor' struct,
>>> as it is a fixed factor clock based on the "pll-video0-4x" clock, created with the CLK_FIXED_FACTOR_HWS macro.
>>> This results in undefined behavior as the hw_to_ccu_common returns an invalid pointer referencing memory before the
>>> 'clk_fixed_factor' struct.
>>>
>>
>> Great catch! At first glance, it seems to me that calling
>> clk_hw_set_rate_range() in sunxi_ccu_probe() should not have happenend
>> in the loop that iterates over the hw_clks.
>>
>> Instead we should add one more loop that iterates over the ccu_clks.
>> Note, that there is already one such loop but, unfortunately, we can't
>> use that as it happens before the hw_clks loop and we can only call
>> clk_hw_set_rate_range() after the hw_clk has been registered.
>>
>> Hence, I propose to move the offending code to a new loop:
>>         for (i = 0; i < desc->num_ccu_clks; i++) {
>>                 struct ccu_common *cclk = desc->ccu_clks[i];
>>
>>                 if (!cclk)
>>                         continue;
>>
>>                 if (cclk->max_rate)
>>                         clk_hw_set_rate_range(&cclk->hw, common->min_rate,
>>                                               common->max_rate);
>>                 else
>>                         WARN(cclk->min_rate,
>>                              "No max_rate, ignoring min_rate of clock %d - %s\n",
>>                              i, cclk->hw.init->name);
>>         }
>>
>> I haven't tested (or even compiled) the above, but I'll test and send a
>> patch within the next few days for you to test.
>>
>> Thanks again,
>>   Frank
>>
>>>
>>> I have attached kernel warnings from a system based on the "sun8i-t113s.dtsi" device tree, where the memory contains
>>> a non-zero value for the min-rate but a zero value for the max-rate, triggering the "No max_rate, ignoring min_rate"
>>> warning in the 'sunxi_ccu_probe' function.
>>>
>>> [...]