Re: [PATCH 2/3] platform/x86: intel_scu_ipc: Check status upon timeout in ipc_wait_for_interrupt()

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Aug 30, 2023 at 06:14:02PM -0700, Stephen Boyd wrote:
> It's possible for the completion in ipc_wait_for_interrupt() to timeout,
> simply because the interrupt was delayed in being processed. A timeout
> in itself is not an error. This driver should check the status register
> upon a timeout to ensure that scheduling or interrupt processing delays
> don't affect the outcome of the IPC return value.
> 
>  CPU0                                                   SCU
>  ----                                                   ---
>  ipc_wait_for_interrupt()
>   wait_for_completion_timeout(&scu->cmd_complete)
>   [TIMEOUT]                                             status[IPC_BUSY]=0
> 
> Fix this problem by reading the status bit in all cases, regardless of
> the timeout. If the completion times out, we'll assume the problem was
> that the IPC_BUSY bit was still set, but if the status bit is cleared in
> the meantime we know that we hit some scheduling delay and we should
> just check the error bit.
> 
> Cc: Prashant Malani <pmalani@chromium.org>
> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>