linux-kernel - Re: [PATCH 1/3] platform/x86: intel_scu_ipc: Check status after timeouts in busy

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Message-ID: <ZPiCz6AaLc4mqGH8@smile.fi.intel.com>
Date:   Wed, 6 Sep 2023 16:46:55 +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 1/3] platform/x86: intel_scu_ipc: Check status after
 timeouts in busy_loop()

On Tue, Sep 05, 2023 at 05:27:23PM -0500, Stephen Boyd wrote:
> Quoting Mika Westerberg (2023-08-31 22:50:11)
> > On Wed, Aug 30, 2023 at 06:14:01PM -0700, 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);
> > >   <long time scheduled away>
> > >   if (!(status & IPC_STATUS_BUSY))
> >
> > How can the status bit change here as we are the only user and the SCU
> > access is serialized by ipclock?
> 
> I don't know how the SCU works. I thought that IPC_STATUS_BUSY bit was
> cleared by the SCU when it was done processing. With that assumption, I
> tried to show that the status is read and then the process schedules
> away for a long time and has an outdated view of the busy bit.

We probably have different versions of firmwares for the different SoC
generations. But I _think_ that you are right, the SCU firmware should
clear the bit when it's done.

-- 
With Best Regards,
Andy Shevchenko