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Date:   Tue, 10 Oct 2023 10:52:09 +0200
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Subject: Re: [PATCH v3] spmi: mtk-pmif: Serialize PMIF status check and
 command submission
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        <nfraprado@collabora.com>, Stephen Boyd <sboyd@kernel.org>
Cc:     Chen-Yu Tsai <wenst@google.com>, kernel@collabora.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>,
        James Lo <james.lo@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
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 <7b407eda-702a-444a-b644-5e8dc31f3991@notapiano>
From:   AngeloGioacchino Del Regno <angelogioacchino.delregno@kernel.org>
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Il 19/09/23 22:12, Nícolas F. R. A. Prado ha scritto:
> On Thu, Aug 10, 2023 at 06:03:53PM -0400, Nícolas F. R. A. Prado wrote:
>> On Mon, Jul 24, 2023 at 11:47:33AM -0400, Nícolas F. R. A. Prado wrote:
>>> Before writing the read or write command to the SPMI arbiter through the
>>> PMIF interface, the current status of the channel is checked to ensure
>>> it is idle. However, since the status only changes from idle when the
>>> command is written, it is possible for two concurrent calls to determine
>>> that the channel is idle and simultaneously send their commands. At this
>>> point the PMIF interface hangs, with the status register no longer being
>>> updated, and thus causing all subsequent operations to time out.
>>>
>>> This was observed on the mt8195-cherry-tomato-r2 machine, particularly
>>> after commit 46600ab142f8 ("regulator: Set PROBE_PREFER_ASYNCHRONOUS for
>>> drivers between 5.10 and 5.15") was applied, since then the two MT6315
>>> devices present on the SPMI bus would probe assynchronously and
>>> sometimes (during probe or at a later point) read the bus
>>> simultaneously, breaking the PMIF interface and consequently slowing
>>> down the whole system.
>>>
>>> To fix the issue at its root cause, introduce locking around the channel
>>> status check and the command write, so that both become an atomic
>>> operation, preventing race conditions between two (or more) SPMI bus
>>> read/write operations. A spinlock is used since this is a fast bus, as
>>> indicated by the usage of the atomic variant of readl_poll, and
>>> '.fast_io = true' being used in the mt6315 driver, so spinlocks are
>>> already used for the regmap access.
>>>
>>> Fixes: b45b3ccef8c0 ("spmi: mediatek: Add support for MT6873/8192")
>>> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
>>
>> Hi,
>>
>> gentle ping on this one. MT8195 Chromebooks sometimes boot to a broken state
>> without it.
> 
> Hi Stephen,
> 
> once again kindling reminding you of this important fix for MediaTek platforms,
> solving a real issue impacting basic functionality observed on the MT8195
> Chromebook.
> 

Hello Stephen,

can you please pick this one ASAP?
MT8195 is broken without.

Thanks,
Angelo