Re: [PATCH v2 2/2] clk: mediatek: mt8365: Fix index issue

From: Alexandre Mergnat <amergnat@baylibre.com>
To: AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Chen-Yu Tsai <wenst@chromium.org>
Cc: Markus Schneider-Pargmann <msp@baylibre.com>,
	linux-clk@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org
Subject: Re: [PATCH v2 2/2] clk: mediatek: mt8365: Fix index issue
Date: Fri, 26 May 2023 11:38:53 +0200	[thread overview]
Message-ID: <d2ed4cce-108f-c861-5f84-0c7ac5954346@baylibre.com> (raw)
In-Reply-To: <2a60740f-782d-08d5-f62f-dcc67aaf4d32@collabora.com>

On 26/05/2023 10:33, AngeloGioacchino Del Regno wrote:
> Il 25/05/23 16:50, Alexandre Mergnat ha scritto:
>> Before the patch [1], the clock probe was done directly in the
>> clk-mt8365 driver. In this probe function, the array which stores the
>> data clocks is sized using the higher defined numbers (*_NR_CLOCK) in
>> the clock lists [2]. Currently, with the patch [1], the specific
>> clk-mt8365 probe function is replaced by the mtk generic one [3], which
>> size the clock data array by adding all the clock descriptor array size
>> provided by the clk-mt8365 driver.
>>
>> Actually, all clock indexes come from the header file [2], that mean, if
>> there are more clock (then more index) in the header file [2] than the
>> number of clock declared in the clock descriptor arrays (which is the
>> case currently), the clock data array will be undersized and then the
>> generic probe function will overflow when it will try to write in
>> "clk_data[CLK_INDEX]". Actually, instead of crashing at boot, the probe
>> function returns an error in the log which looks like:
>> "of_clk_hw_onecell_get: invalid index 135", then this clock isn't
>> enabled.
>>
>> Solve this issue by adding in the driver the missing clocks declared in
>> the header clock file [2].
>>
>> [1]: Commit ffe91cb28f6a ("clk: mediatek: mt8365: Convert to
>>       mtk_clk_simple_{probe,remove}()")
>> [2]: include/dt-bindings/clock/mediatek,mt8365-clk.h
>> [3]: drivers/clk/mediatek/clk-mtk.c
>>
>> Fixes: ffe91cb28f6a ("clk: mediatek: mt8365: Convert to 
>> mtk_clk_simple_{probe,remove}()")
>
> This is not fixing the conversion, but the clock driver, as it 
> originally missed
> clock entries and hence was not compliant with its binding (header).
> It worked before, probably, but this doesn't mean that this driver 
> didn't contain
> a logic mistake from the beginning :-)
>
> So, add (or replace the current one with) the relevant Fixes tag...
>

Briefly and factually, the mt8365 clk probe mechanism was different

compared to the mtk clk driver. Even if it was an issue or not, it was

working (for sure). When [1] improved the mt8365 clk driver by using

the mtk clk generic probe, some clocks (USB here) no longer worked.

So, IMHO, it still a functional regression introduced by [1], because it

come from the switch of the probe function.

I'm not blaming & shaming the author of [1], as you said, it originally

missed clock entries and hence was not compliant with its binding

(whereas other MTK SoC was I guess). This commit is pointed thanks

to the bisect + test.

-- 
Regards,
Alexandre