Re: [PATCH 1/8] spmi: mtk-pmif: Serialize PMIF status check and command submission

Greg Kroah-Hartman
2023-12-15T16:12:32Z

On Wed, Dec 06, 2023 at 03:17:24PM -0800, Stephen Boyd wrote:
> From: Nícolas F. R. A. Prado <nfraprado@collabora.com>
>
> 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>
> Link: https://lore.kernel.org/r/20230724154739.493724-1-nfraprado@collabora.com
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
> Signed-off-by: Stephen Boyd <sboyd@kernel.org>
> ---
> drivers/spmi/spmi-mtk-pmif.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him
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