linux-kernel - Re: [PATCH v2 3/3] platform/x86: intel_scu

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Message-ID: <CAE-0n53iGCL3q=CsDKZr28eMjx40miLNG6+-jf12JKMxuAKkKg@mail.gmail.com>
Date:   Wed, 6 Sep 2023 15:22:43 -0500
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
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 v2 3/3] platform/x86: intel_scu_ipc: Fail IPC send if
 still busy

Quoting Andy Shevchenko (2023-09-06 13:13:27)
> On Wed, Sep 06, 2023 at 11:09:43AM -0700, Stephen Boyd wrote:
> > It's possible for interrupts to get significantly delayed to the point
> > that callers of intel_scu_ipc_dev_command() and friends can call the
> > function once, hit a timeout, and call it again while the interrupt
> > still hasn't been processed. This driver will get seriously confused if
> > the interrupt is finally processed after the second IPC has been sent
> > with ipc_command(). It won't know which IPC has been completed. This
> > could be quite disastrous if calling code assumes something has happened
> > upon return from intel_scu_ipc_dev_simple_command() when it actually
> > hasn't.
> >
> > Let's avoid this scenario by simply returning -EBUSY in this case.
> > Hopefully higher layers will know to back off or fail gracefully when
> > this happens. It's all highly unlikely anyway, but it's better to be
> > correct here as we have no way to know which IPC the status register is
> > telling us about if we send a second IPC while the previous IPC is still
> > processing.
>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>
> Also see below.
>
> ...
>
> > @@ -450,6 +468,12 @@ int intel_scu_ipc_dev_simple_command(struct intel_scu_ipc_dev *scu, int cmd,
> >               return -ENODEV;
> >       }
>
> >       scu = ipcdev;
>
> Side observation: Isn't this a bug? We should not override the supplied parameter.

If it is a bug that would be great to know. I wanted to make an API that
got the scu if it wasn't busy but then I ran across this code that
replaced the scu with ipcdev.