[GICv3 ITS]S2IDLE framework does not invoke syscore_ops in GICv3 ITS driver

[Youngmin Nam]

On Wed, Mar 26, 2025 at 08:59:02AM +0000, Marc Zyngier wrote:
> On Wed, 26 Mar 2025 03:09:37 +0000,
> Youngmin Nam <youngmin.nam at samsung.com> wrote:
> > 
> > Hi.
> > 
> > On our SoC, we are using S2IDLE instead of S2R as a system suspend mode.
> > However, when I try to enable ARM GICv3 ITS driver (drivers/irqchip/irq-gic-v3-its.c),
> > I noticed that there is no proper way to invoke suspend/resume callback,
> > because it only uses syscore_ops, which is not called in an s2idle scenario.
> 
> This is *by design*.
> 
> > Please refer to the codes below.
> > 
> > <drivers/irqchip/irq-gic-v3-its.c>
> > 5028 static struct syscore_ops its_syscore_ops = {
> > 5029         .suspend = its_save_disable,
> > 5030         .resume = its_restore_enable,
> > 5031 };
> > ...
> > 5803         register_syscore_ops(&its_syscore_ops);
> > 
> > <kernel/power/suspend.c>
> > 444         if (state == PM_SUSPEND_TO_IDLE) {
> > 445                 s2idle_loop();
> > 446                 goto Platform_wake;
> > 447         }
> > 448
> > 449         error = pm_sleep_disable_secondary_cpus();
> > 450         if (error || suspend_test(TEST_CPUS)) {
> > 451                 log_suspend_abort_reason("Disabling non-boot cpus failed");
> > 452                 goto Enable_cpus;
> > 453         }
> > 454
> > 455         arch_suspend_disable_irqs();
> > 456         BUG_ON(!irqs_disabled());
> > 457
> > 458         system_state = SYSTEM_SUSPEND;
> > 459
> > 460         error = syscore_suspend();
> > 
> > How should we handle this situation ?
> 
> By implementing anything related to GIC power-management in your EL3
> firmware. Only your firmware knows whether you are going into a state
> where the GIC (and the ITS) is going to lose its state (because power
> is going to be removed) or if the sleep period is short enough that
> you can come back from idle without loss of context.
> 
> Furthermore, there is a lot of things that non-secure cannot do when
> it comes to GIC power management (most the controls are secure only),
> so it is pretty clear that the kernel is the wrong place for this.
> 
> I'd suggest you look at what TF-A provides, because this is not
> exactly a new problem (it has been solved several years ago).
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.
> 

Hi Marc,

First of all, I’d like to distinguish between the GICv3 driver (irq-gic-v3.c)
and the ITS driver (irq-gic-v3-its.c).

I now understand why the GICv3 driver doesn’t implement suspend and resume functions.
However, unlike the GICv3 driver, the ITS driver currently provides
suspend and resume functions via syscore_ops in the kernel.
And AFAIK, LPIs are always treated as non-secure. (Please correct me If I'm wrong).

The problem is that syscore_ops is not invoked during the S2IDLE scenario,
so we cannot rely on it in that context.
We would like to use these suspend/resume functions during S2IDLE as well.

Thanks.