Re: [PATCH v3 3/7] arm64: Add helpers for detecting AArch32 support at EL0

[Suzuki K Poulose]

On 14/04/16 17:39, Will Deacon wrote:
> On Thu, Mar 31, 2016 at 06:27:31PM +0100, Suzuki K Poulose wrote:
> > Adds a helper to extract the support for AArch32 at EL0
> >
> > Tested-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

> > +static inline bool id_aa64pfr0_32bit_el0(u64 pfr0)
> > +{
> > +	u32 val = cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_EL0_SHIFT);
> > +
> > +	return val == ID_AA64PFR0_EL0_32BIT_64BIT;
>
> Should this be >=? What are the rules for this register?

This feature value is kind of "FTR_EXACT" where, we don't know what the relationship
of the values are. Here is the list of possible values :

0001	EL0 can be executed in AArch64 state only.
0010	EL0 can be executed in either AArch64 or AArch32 state.

All the other values are reserved. So I believe "==" is better check.

Suzuki