linux-kernel - Re: [PATCH 2/3] platform/x86: intel_scu_ipc: Check status upon timeout in ipc_wait_for

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Message-ID: <ZPCcevAt4CwCADe2@smile.fi.intel.com>
Date:   Thu, 31 Aug 2023 16:58:18 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        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,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Prashant Malani <pmalani@...omium.org>
Subject: Re: [PATCH 2/3] platform/x86: intel_scu_ipc: Check status upon
 timeout in ipc_wait_for_interrupt()

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.

Makes sense, thanks for fixing this!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Also see below.

...

>  /* Wait till ipc ioc interrupt is received or timeout in 10 HZ */

Not sure if this comment needs to be updated / amended.

...

>  	status = ipc_read_status(scu);
> -	if (status & IPC_STATUS_ERR)
> -		return -EIO;
> +	if (!(status & IPC_STATUS_BUSY))
> +		err = (status & IPC_STATUS_ERR) ? -EIO : 0;
>  
> -	return 0;
> +	return err;

I would write it as:

	status = ipc_read_status(scu);
	if (status & IPC_STATUS_BUSY)
		return 0;
	if (status & IPC_STATUS_ERR)
		return -EIO;

	return 0;

Also would be good, in case you are not doing it yet, to use --patience when
formatting your patches.

-- 
With Best Regards,
Andy Shevchenko