Re: [PATCH v4 02/26] arm64: cpufeature: Add cpufeature for IRQ priority masking

[Suzuki K Poulose]

On 25/05/18 11:17, Julien Thierry wrote:
> On 25/05/18 11:04, Suzuki K Poulose wrote:
> > On 25/05/18 10:49, Julien Thierry wrote:
> > > Add a cpufeature indicating whether a cpu supports masking interrupts
> > > by priority.
> >
> > How is this different from the SYSREG_GIC_CPUIF cap ? Is it just
> > the description ?
>
> More or less.
>
> It is just to have an easier condition in the rest of the series. Basically the PRIO masking feature is enabled if we have a GICv3 CPUIF working *and* the option was selected at build time. Before this meant that I was checking for the GIC_CPUIF cap inside #ifdefs (and putting alternatives depending on that inside #ifdefs as well).
>
> Having this as a separate feature feels easier to manage in the code. It also makes it clearer at boot time that the kernel will be using irq priorities (although I admit it was not the initial intention):
>
> [ÂÂÂ 0.000000] CPU features: detected: IRQ priority masking
>
>
> But yes that new feature will be detected only if SYSREG_GIC_CPUIF gets detected as well.

Well, you could always wrap the check like :

static inline bool system_has_irq_priority_masking(void)
{
	return (IS_ENABLED(CONFIG_YOUR_CONFIG) && cpus_have_const_cap(HWCAP_SYSREG_GIC_CPUIF));
}

and use it everywhere.

The description could be statically changed to reflect based on the #ifdef.


static const struct arm64_cpu_capabilities arm64_features[] = {
        {
#ifdef CONFIG_YOUR_CONFIG
		.desc = "GIC System register CPU interface with IRQ priority masking"
#else
                .desc = "GIC system register CPU interface",
#endif
                .capability = ARM64_HAS_SYSREG_GIC_CPUIF,
                .type = ARM64_CPUCAP_SYSTEM_FEATURE,
                .matches = has_useable_gicv3_cpuif,
                .sys_reg = SYS_ID_AA64PFR0_EL1,
                .field_pos = ID_AA64PFR0_GIC_SHIFT,
                .sign = FTR_UNSIGNED,
                .min_field_value = 1,

Cheers
Suzuki