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

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Message-ID: <d2ed4cce-108f-c861-5f84-0c7ac5954346@baylibre.com>
Date:   Fri, 26 May 2023 11:38:53 +0200
From:   Alexandre Mergnat <amergnat@...libre.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chen-Yu Tsai <wenst@...omium.org>
Cc:     Markus Schneider-Pargmann <msp@...libre.com>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] clk: mediatek: mt8365: Fix index issue


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