Re: [PATCH v2 06/17] irqchip/gic-v3: Configure SGIs as standard interrupts

[Valentin Schneider]

On 30/06/20 11:15, Marc Zyngier wrote:
> On 2020-06-25 19:25, Valentin Schneider wrote:
>> Also, while staring at this it dawned on me that IPI's don't need the
>> eoimode=0 isb(): due to how the IPI flow-handler is structured, we'll
>> get a
>> gic_eoi_irq() just before calling into the irqaction. Dunno how much we
>> care about it.
>
> That's interesting. This ISB is a leftover from the loop we had before
> the pseudo-NMI code, where we had to make sure the write to EOIR was
> ordered with the read from IAR.
>
> Given that we have an exception return right after the interrupt
> handling, I *think* we could get rid of it (but that would need
> mode checking on broken systems such as TX1...).  I don't think
> this is specific to IPIs though.
>

If I got this one right:

  39a06b67c2c1 ("irqchip/gic: Ensure we have an ISB between ack and ->handle_irq")

you're describing case 2, which is indeed gone on gic-v3. However IIUC we
also want an ISB between poking IAR and calling into the irqaction (case 1)
- we get just that with IPIs due to the early gic_eoi_irq(), but we don't
for the other flows.

> Thanks,
>
>          M.