linux-kernel - Re: [PATCH v3 2/4] platform/x86: intel_scu_ipc: Check status upon timeout in ipc_wait_for

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Message-ID: <20230912050045.GA1599918@black.fi.intel.com>
Date:   Tue, 12 Sep 2023 08:00:45 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        platform-driver-x86@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Prashant Malani <pmalani@...omium.org>
Subject: Re: [PATCH v3 2/4] platform/x86: intel_scu_ipc: Check status upon
 timeout in ipc_wait_for_interrupt()

On Mon, Sep 11, 2023 at 12:39:34PM -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_STATUS_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_STATUS_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@...omium.org>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

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