Messages in this thread | | | Date | Fri, 11 Aug 2023 13:09:17 +0200 | Subject | Re: [PATCH v3] spmi: mtk-pmif: Serialize PMIF status check and command submission | From | Alexandre Mergnat <> |
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Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
On 24/07/2023 17:47, 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.
-- Regards, Alexandre
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