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

[Suzuki K Poulose]

On 12/06/18 14:46, Julien Thierry wrote:
> On 25/05/18 11:48, Julien Thierry wrote:
> > On 25/05/18 11:41, Suzuki K Poulose wrote:
> > > On 25/05/18 11:39, Julien Thierry wrote:
> > > > 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)
> > > > > {
> > > > > ÂÂÂÂÂreturn (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... :\
> > >
> > > I thought there is _ALTERNATIVE_CFG() to base the alternative depend on a CONFIG_xxx ?
> > > Doesn't that solve the problem ?
> >
> > Right, I didn't see that one. It should work yes.
> >
> > I'll try that when working on the next version.
>
> I've been trying to use this now, but I can't figure out how.
>
> The _ALTERNATIVE_CFG does not seem to work in assembly code (despite having its own definition for __ASSEMBLY__), and the alternative_insn does not seem to be suited for instructions that take operands (or more than one operand)
>
> If I am mistaken, can you provide an example of how to use this in assembly with instructions having more than 1 operand?

I am sorry, but I think the ALTERNATIVE_CFG is not the right one, as it
omits the entire block, if the CONFIG is not enabled. So you are left with
only three choices :

1) Use alternative call back
2) Stick to two separate caps.
3) Use #ifdef

Cheers
Suzuki