Re: [PATCH 05/16] arm64: Add flags to check the safety of a capability for late CPU

[Suzuki K Poulose]

On 26/01/18 10:10, Dave Martin wrote:
> On Tue, Jan 23, 2018 at 12:27:58PM +0000, Suzuki K Poulose wrote:
> > Add two different flags to indicate if the conflict of a capability
> > on a late CPU with the current system state
> >
> >   1) Can a CPU have a capability when the system doesn't have it ?
> >
> >      Most arm64 features could have this set. While erratum work arounds
> >      cannot have this, as we may miss work arounds.
> >
> >   2) Can a CPU miss a capability when the system has it ?
> >      This could be set for arm64 erratum work arounds as we don't
> >      care if a CPU doesn't need the work around. However it should
> >      be clear for features.
> >
> > These flags could be added to certain entries based on their nature.
> >
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   arch/arm64/include/asm/cpufeature.h | 35 +++++++++++++++++++++++++++++++----
> >   1 file changed, 31 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> > index 4fd5de8ef33e..27d037bb0451 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -94,10 +94,25 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
> >   #define SCOPE_SYSTEM				ARM64_CPUCAP_SCOPE_SYSTEM
> >   #define SCOPE_LOCAL_CPU				ARM64_CPUCAP_SCOPE_LOCAL_CPU
> >   
> > -/* CPU errata detected at boot time based on feature of one or more CPUs */
> > -#define ARM64_CPUCAP_STRICT_CPU_LOCAL_ERRATUM	(ARM64_CPUCAP_SCOPE_LOCAL_CPU)
> > -/* CPU feature detected at boot time based on system-wide value of a feature */
> > -#define ARM64_CPUCAP_BOOT_SYSTEM_FEATURE	(ARM64_CPUCAP_SCOPE_SYSTEM)
> > +/* Is it safe for a late CPU to have this capability when system doesn't already have */
> > +#define ARM64_CPUCAP_LATE_CPU_SAFE_TO_HAVE	BIT(2)
> > +/* Is it safe for a late CPU to miss this capability when system has it */
> > +#define ARM64_CPUCAP_LATE_CPU_SAFE_TO_MISS	BIT(3)
>
> Maybe _OPTIONAL and _PERMITTED would be a bit less verbose?
>
> Alternatively,
> 	ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU
> 	ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU

Sounds better than what I have. I have picked them up.

Cheers
Suzuki