Re: [PATCH 3/3] platform/x86: intel_scu_ipc: Fail IPC send if still busy

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On Wed, Aug 30, 2023 at 06:14:03PM -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 bool intel_scu_ipc_busy(struct intel_scu_ipc_dev *scu)

static int ?

> +{
> +	u8 status;
> +
> +	status = ipc_read_status(scu);
> +	if (status & IPC_STATUS_BUSY) {

> +		dev_err(&scu->dev, "device is busy\n");

1. Wouldn't it exaggerate the logs? Shouldn't be rate limited?
2. OTOH if we return -EBUSY directly from here, do we need this at all?

> +		return true;
> +	}
> +
> +	return false;
> +}

With Best Regards,
Andy Shevchenko

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