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Subject[PATCH v2 1/3] drivers: clocksource: configure event stream for ARM arch timer
Date
From: Will Deacon <will.deacon@arm.com>

The ARM architected timer can generate events (used for waking up
CPUs executing the wfe instruction) at a frequency represented as a
power-of-2 divisor of the clock rate.

This patch configures the event stream, aiming for a period of 100us
between events. This can be used to implement wfe-based timeouts for
userspace locking implementations.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm/include/asm/arch_timer.h | 5 +++--
arch/arm64/include/asm/arch_timer.h | 6 +++---
drivers/clocksource/arm_arch_timer.c | 9 ++++++++-
include/clocksource/arm_arch_timer.h | 2 ++
4 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index e406d57..c3d9ef7 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -89,14 +89,15 @@ static inline u64 arch_counter_get_cntvct(void)
return cval;
}

-static inline void arch_counter_set_user_access(void)
+static inline void arch_counter_set_user_access(int divider)
{
u32 cntkctl;

asm volatile("mrc p15, 0, %0, c14, c1, 0" : "=r" (cntkctl));

/* disable user access to everything */
- cntkctl &= ~((3 << 8) | (7 << 0));
+ cntkctl &= ~((3 << 8) | (0xf << 4) | (3 << 0));
+ cntkctl |= (divider << 4) | (1 << 2);

asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
}
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 98abd47..8c1e42f 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -97,16 +97,16 @@ static inline u32 arch_timer_get_cntfrq(void)
return val;
}

-static inline void arch_counter_set_user_access(void)
+static inline void arch_counter_set_user_access(int divider)
{
u32 cntkctl;

/* Disable user access to the timers and the physical counter. */
asm volatile("mrs %0, cntkctl_el1" : "=r" (cntkctl));
- cntkctl &= ~((3 << 8) | (1 << 0));
+ cntkctl &= ~((3 << 8) | (0xf << 4) | (1 << 0));

/* Enable user access to the virtual counter and frequency. */
- cntkctl |= (1 << 1);
+ cntkctl |= (divider << 4) | (1 << 2) | (1 << 1);
asm volatile("msr cntkctl_el1, %0" : : "r" (cntkctl));
}

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index ffadd83..6301ee5 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -125,6 +125,8 @@ static int arch_timer_set_next_event_phys(unsigned long evt,

static int arch_timer_setup(struct clock_event_device *clk)
{
+ int evt_stream_div, pos;
+
clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP;
clk->name = "arch_sys_timer";
clk->rating = 450;
@@ -153,7 +155,12 @@ static int arch_timer_setup(struct clock_event_device *clk)
enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
}

- arch_counter_set_user_access();
+ /* Find the closest power of two to the divisor */
+ evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+ pos = fls(evt_stream_div);
+ if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+ pos--;
+ arch_counter_set_user_access(min(pos, 15));

return 0;
}
diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index c463ce9..24dc140 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -29,6 +29,8 @@
#define ARCH_TIMER_PHYS_ACCESS 0
#define ARCH_TIMER_VIRT_ACCESS 1

+#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */
+
#ifdef CONFIG_ARM_ARCH_TIMER

extern u32 arch_timer_get_rate(void);
--
1.8.1.2



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