Hi Drew,
On 16/11/16 14:38, Andrew Jones wrote:
> ARMv7-A isn't exactly the same as ARMv8-A32 (AArch32). This
> function allows unit tests to make the distinction.
So the big question here is why you would like to know this?
If it is for a certain feature, you should check for that instead.
> Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
>
> ---
> I'm actually unsure if there's a feature bit or not that I could
> probe instead. It'd be nice if somebody can confirm. Thanks, drew
Probing for a Cortex-A15 is definitely not the right thing. I think
under KVM you'd see Cortex-A7 and Cortex-A12/A17 if you run on one of those.
So there does not seem to be a dedicated feature bit, however you could
look for some ISA features that ARMv8 AA32 gained over ARMv7.
So one thing you could check for is ID_ISAR5[3:0] (SEVL).
The ARMv7 ARM says that this whole register is "Reserved, UNK", which
technically doesn't give you a lot to check for. But I guess it just
reads as zero on ARMv7 ;-)
The ARMv8 ARM on the other hands puts ARMv8 features in there, among the
new crypto instructions (which are optional), there is the SEVL
instruction, which the architecture mandates:
"In ARMv8-A the only permitted value is 0001."
So I guess the closest you could come to is to check for the lowest 4
bits of ID_ISAR5 to read as '0001'.
HTH,
Andre.
> lib/arm/asm/processor.h | 20 ++++++++++++++++++++
> lib/arm64/asm/processor.h | 5 +++++
> 2 files changed, 25 insertions(+)
>
> diff --git a/lib/arm/asm/processor.h b/lib/arm/asm/processor.h
> index f25e7eee3666..223e54beb72a 100644
> --- a/lib/arm/asm/processor.h
> +++ b/lib/arm/asm/processor.h
> @@ -5,6 +5,7 @@
> *
> * This work is licensed under the terms of the GNU LGPL, version 2.
> */
> +#include <bitops.h>
> #include <asm/ptrace.h>
>
> enum vector {
> @@ -46,4 +47,23 @@ static inline unsigned int get_mpidr(void)
> extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr);
> extern bool is_user(void);
>
> +/*
> + * ARMv7-A isn't exactly the same as ARMv8-A32 (AArch32). This
> + * function allows unit tests to make the distinction.
> + */
> +static inline bool is_aarch32(void)
> +{
> + /*
> + * XXX: Unfortunately there's no feature bit we can probe for
> + * this, so we do a hacky check for the processor type not being
> + * a Cortex-A15, which is the only v7 type we currently use.
> + */
> + unsigned long midr;
> +
> + asm volatile("MRC p15, 0, %0, c0, c0, 0" : "=r" (midr));
> + midr &= GENMASK(31, 24) | GENMASK(15, 4);
> +
> + return midr != ((0x41 << 24) | (0xc0f << 4));
> +}
> +
> #endif /* _ASMARM_PROCESSOR_H_ */
> diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
> index 84d5c7ce752b..b602e1fbbc2d 100644
> --- a/lib/arm64/asm/processor.h
> +++ b/lib/arm64/asm/processor.h
> @@ -81,5 +81,10 @@ DEFINE_GET_SYSREG32(mpidr)
> extern void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr);
> extern bool is_user(void);
>
> +static inline bool is_aarch32(void)
> +{
> + return false;
> +}
> +
> #endif /* !__ASSEMBLY__ */
> #endif /* _ASMARM64_PROCESSOR_H_ */
>
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