linux-kernel - Re: [PATCH v3 4/4] platform/x86: intel_scu

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Message-ID: <ZP+FHs+GBROf0zH8@smile.fi.intel.com>
Date:   Tue, 12 Sep 2023 00:22:38 +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 v3 4/4] platform/x86: intel_scu_ipc: Fail IPC send if
 still busy

On Mon, Sep 11, 2023 at 12:39:36PM -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.

...

> +static struct intel_scu_ipc_dev *intel_scu_ipc_get(struct intel_scu_ipc_dev *scu)
> +{
> +	u8 status;

> +	if (!scu)
> +		scu = ipcdev;

I would write this as

	scu = scu ?: ipcdev;

> +	if (!scu)
> +		return ERR_PTR(-ENODEV);
> +
> +	status = ipc_read_status(scu);
> +	if (status & IPC_STATUS_BUSY) {
> +		dev_dbg(&scu->dev, "device is busy\n");
> +		return ERR_PTR(-EBUSY);
> +	}
> +
> +	return scu;
> +}

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

-- 
With Best Regards,
Andy Shevchenko