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

[Mika Westerberg]

On Thu, Aug 31, 2023 at 05:07:26PM +0300, Andy Shevchenko wrote:
> 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?

Agree w/ returning -EBUSY here and dropping the dev_err() (or using
dev_dbg()).