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Subject[PATCH v2 13/18] arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs
Date
Instead of applying a CPU-specific workaround to all CPUs in the system,
allow it to only affect a subset of them (typical big-little case).

This is done by turning the erratum pointer into a per-CPU variable.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/include/asm/arch_timer.h | 31 ++++++++++++++++----------
drivers/clocksource/arm_arch_timer.c | 42 +++++++++++++++++++++++++-----------
2 files changed, 50 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index d46cf21e8b80..3cba3a5e4ba1 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -25,6 +25,7 @@
#include <linux/bug.h>
#include <linux/init.h>
#include <linux/jump_label.h>
+#include <linux/smp.h>
#include <linux/types.h>

#include <clocksource/arm_arch_timer.h>
@@ -56,17 +57,25 @@ struct arch_timer_erratum_workaround {
int (*set_next_event_virt)(unsigned long, struct clock_event_device *);
};

-extern const struct arch_timer_erratum_workaround *timer_unstable_counter_workaround;
-
-#define arch_timer_reg_read_stable(reg) \
-({ \
- u64 _val; \
- if (needs_unstable_timer_counter_workaround() && \
- timer_unstable_counter_workaround->read_##reg) \
- _val = timer_unstable_counter_workaround->read_##reg(); \
- else \
- _val = read_sysreg(reg); \
- _val; \
+DECLARE_PER_CPU(const struct arch_timer_erratum_workaround *,
+ timer_unstable_counter_workaround);
+
+#define arch_timer_reg_read_stable(reg) \
+({ \
+ u64 _val; \
+ if (needs_unstable_timer_counter_workaround()) { \
+ const struct arch_timer_erratum_workaround *wa; \
+ preempt_disable(); \
+ wa = __this_cpu_read(timer_unstable_counter_workaround); \
+ if (wa && wa->read_##reg) \
+ _val = wa->read_##reg(); \
+ else \
+ _val = read_sysreg(reg); \
+ preempt_enable(); \
+ } else { \
+ _val = read_sysreg(reg); \
+ } \
+ _val; \
})

/*
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index b9f01daafdfa..2b17b99922a1 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -235,7 +235,8 @@ static u64 notrace hisi_161010101_read_cntvct_el0(void)
#endif

#ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
-const struct arch_timer_erratum_workaround *timer_unstable_counter_workaround = NULL;
+DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *,
+ timer_unstable_counter_workaround);
EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);

DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
@@ -345,9 +346,18 @@ arch_timer_iterate_errata(enum arch_timer_erratum_match_type type,
}

static
-void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa)
+void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa,
+ bool local)
{
- timer_unstable_counter_workaround = wa;
+ int i;
+
+ if (local) {
+ __this_cpu_write(timer_unstable_counter_workaround, wa);
+ } else {
+ for_each_possible_cpu(i)
+ per_cpu(timer_unstable_counter_workaround, i) = wa;
+ }
+
static_branch_enable(&arch_timer_read_ool_enabled);
}

@@ -376,14 +386,17 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
return;

if (static_branch_unlikely(&arch_timer_read_ool_enabled)) {
- if (wa != timer_unstable_counter_workaround)
+ const struct arch_timer_erratum_workaround *__wa;
+ __wa = __this_cpu_read(timer_unstable_counter_workaround);
+ if (__wa && wa != __wa)
pr_warn("Can't enable workaround for %s (clashes with %s\n)",
- wa->desc,
- timer_unstable_counter_workaround->desc);
- return;
+ wa->desc, __wa->desc);
+
+ if (__wa)
+ return;
}

- arch_timer_enable_workaround(wa);
+ arch_timer_enable_workaround(wa, local);
pr_info("Enabling %s workaround for %s\n",
local ? "local" : "global", wa->desc);
}
@@ -391,10 +404,15 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
#define erratum_handler(fn, r, ...) \
({ \
bool __val; \
- if (needs_unstable_timer_counter_workaround() && \
- timer_unstable_counter_workaround->fn) { \
- r = timer_unstable_counter_workaround->fn(__VA_ARGS__); \
- __val = true; \
+ if (needs_unstable_timer_counter_workaround()) { \
+ const struct arch_timer_erratum_workaround *__wa; \
+ __wa = __this_cpu_read(timer_unstable_counter_workaround); \
+ if (__wa && __wa->fn) { \
+ r = __wa->fn(__VA_ARGS__); \
+ __val = true; \
+ } else { \
+ __val = false; \
+ } \
} else { \
__val = false; \
} \
--
2.11.0
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