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, 8 insertions, 0 deletions

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index aa4ec53281ce..6cc8aff83805 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -833,7 +833,11 @@ static void arch_timer_evtstrm_enable(int divider)
         cntkctl |= (divider << ARCH_TIMER_EVT_TRIGGER_SHIFT)
                         | ARCH_TIMER_VIRT_EVT_EN;
         arch_timer_set_cntkctl(cntkctl);
+#ifdef CONFIG_ARM64
+        cpu_set_named_feature(EVTSTRM);
+#else
         elf_hwcap |= HWCAP_EVTSTRM;
+#endif
 #ifdef CONFIG_COMPAT
         compat_elf_hwcap |= COMPAT_HWCAP_EVTSTRM;
 #endif
@@ -1055,7 +1059,11 @@ static int arch_timer_cpu_pm_notify(struct notifier_block *self,
         } else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT) {
                 arch_timer_set_cntkctl(__this_cpu_read(saved_cntkctl));
 
+#ifdef CONFIG_ARM64
+                if (cpu_have_named_feature(EVTSTRM))
+#else
                 if (elf_hwcap & HWCAP_EVTSTRM)
+#endif
                         cpumask_set_cpu(smp_processor_id(), &evtstrm_available);
         }
         return NOTIFY_OK;