Re: [PATCH v3 1/4] platform/x86: intel_scu_ipc: Check status after timeout in busy_loop()

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On 9/11/2023 12:39 PM, Stephen Boyd wrote:
> It's possible for the polling loop in busy_loop() to get scheduled away
> for a long time.
>   status = ipc_read_status(scu); // status = IPC_STATUS_BUSY
>   <long time scheduled away>
>   if (!(status & IPC_STATUS_BUSY))
> If this happens, then the status bit could change while the task is
> scheduled away and this function would never read the status again after
> timing out. Instead, the function will return -ETIMEDOUT when it's
> possible that scheduling didn't work out and the status bit was cleared.
> Bit polling code should always check the bit being polled one more time
> after the timeout in case this happens.
> Fix this by reading the status once more after the while loop breaks.
> The read_poll_timeout() macro implements all of this, and it is
> shorter, so use that macro here to consolidate code and fix this.
> There were some concerns with using read_poll_timeout() because it uses
> timekeeping, and timekeeping isn't running early on or during the late
> stages of system suspend or early stages of system resume, but an audit
> of the code concluded that this code isn't called during those times so
> it is safe to use the macro.
> Cc: Prashant Malani <pmalani@xxxxxxxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Fixes: e7b7ab3847c9 ("platform/x86: intel_scu_ipc: Sleeping is fine when polling")
> Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> ---

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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