arm64: HWCAP: add support for AT_HWCAP2

As we will exhaust the first 32 bits of AT_HWCAP let's start
exposing AT_HWCAP2 to userspace to give us up to 64 caps.

Whilst it's possible to use the remaining 32 bits of AT_HWCAP, we
prefer to expand into AT_HWCAP2 in order to provide a consistent
view to userspace between ILP32 and LP64. However internal to the
kernel we prefer to continue to use the full space of elf_hwcap.

To reduce complexity and allow for future expansion, we now
represent hwcaps in the kernel as ordinals and use a
KERNEL_HWCAP_ prefix. This allows us to support automatic feature
based module loading for all our hwcaps.

We introduce cpu_set_feature to set hwcaps which complements the
existing cpu_have_feature helper. These helpers allow us to clean
up existing direct uses of elf_hwcap and reduce any future effort
required to move beyond 64 caps.

For convenience we also introduce cpu_{have,set}_named_feature which
makes use of the cpu_feature macro to allow providing a hwcap name
without a {KERNEL_}HWCAP_ prefix.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
[will: use const_ilog2() and tweak documentation]
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 5ebe73b69961..735cf1f8b109 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1258,14 +1258,14 @@ static inline void fpsimd_hotplug_init(void) { }
  */
 static int __init fpsimd_init(void)
 {
-	if (elf_hwcap & HWCAP_FP) {
+	if (cpu_have_named_feature(FP)) {
 		fpsimd_pm_init();
 		fpsimd_hotplug_init();
 	} else {
 		pr_notice("Floating-point is not implemented\n");
 	}
 
-	if (!(elf_hwcap & HWCAP_ASIMD))
+	if (!cpu_have_named_feature(ASIMD))
 		pr_notice("Advanced SIMD is not implemented\n");
 
 	return sve_sysctl_init();