On Thu, Oct 10, 2019 at 06:15:15PM +0100, Suzuki K Poulose wrote:
> The NO_FPSIMD capability is defined with scope SYSTEM, which implies
> that the "absence" of FP/SIMD on at least one CPU is detected only
> after all the SMP CPUs are brought up. However, we use the status
> of this capability for every context switch. So, let us change
> the scop to LOCAL_CPU to allow the detection of this capability
> as and when the first CPU without FP is brought up.
>
> Also, the current type allows hotplugged CPU to be brought up without
> FP/SIMD when all the current CPUs have FP/SIMD and we have the userspace
> up. Fix both of these issues by changing the capability to
> BOOT_RESTRICTED_LOCAL_CPU_FEATURE.
>
> Fixes: 82e0191a1aa11abf ("arm64: Support systems without FP/ASIMD")
> Cc: Will Deacon <w...@kernel.org>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
> ---
> arch/arm64/kernel/cpufeature.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 9323bcc40a58..0f9eace6c64b 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1361,7 +1361,7 @@ static const struct arm64_cpu_capabilities
> arm64_features[] = {
> {
> /* FP/SIMD is not implemented */
> .capability = ARM64_HAS_NO_FPSIMD,
> - .type = ARM64_CPUCAP_SYSTEM_FEATURE,
> + .type = ARM64_CPUCAP_BOOT_RESTRICTED_CPU_LOCAL_FEATURE,
ARM64_HAS_NO_FPSIMD is really a disability, not a capability.
Although we have other things that smell like this (CPU errata for
example), I wonder whether inverting the meaning in the case would
make the situation easier to understand.
So, we'd have ARM64_HAS_FPSIMD, with a minimum (signed) feature field
value of 0. Then this just looks like an ARM64_CPUCAP_SYSTEM_FEATURE
IIUC. We'd just need to invert the sense of the check in
system_supports_fpsimd().
> .min_field_value = 0,
(Does .min_field_value == 0 make sense, or is it even used? I thought
only the default has_cpuid_feature() match logic uses that.)
> .matches = has_no_fpsimd,
> },
Cheers
---Dave
