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

[Julien Thierry]

On 25/05/18 11:36, Suzuki K Poulose wrote:
> 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)
> {
>  ÂÂÂÂreturn (IS_ENABLED(CONFIG_YOUR_CONFIG) && 
> cpus_have_const_cap(HWCAP_SYSREG_GIC_CPUIF));
> }
>
> and use it everywhere.

Yes, but I can't use that in the asm parts that use alternatives and 
would need to surround them in #ifdef... :\

> The description could be statically changed to reflect based on the #ifdef.
>
>
> static const struct arm64_cpu_capabilities arm64_features[] = {
>  ÂÂÂÂÂÂÂ {
> #ifdef CONFIG_YOUR_CONFIG
>  ÂÂÂÂÂÂÂ .desc = "GIC System register CPU interface with IRQ priority 
> masking"
> #else
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .desc = "GIC system register CPU interface",
> #endif
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .capability = ARM64_HAS_SYSREG_GIC_CPUIF,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .matches = has_useable_gicv3_cpuif,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .sys_reg = SYS_ID_AA64PFR0_EL1,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .field_pos = ID_AA64PFR0_GIC_SHIFT,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .sign = FTR_UNSIGNED,
>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ .min_field_value = 1,
>
> Cheers
> Suzuki

--
Julien Thierry