[PATCH v4] clocksource: arch_timer: Fix code to use physical timers when requested

From: Sonny Rao
Date: Wed Oct 08 2014 - 03:39:11 EST

This is a bug fix for using physical arch timers when
the arch_timer_use_virtual boolean is false. It restores the
arch_counter_get_cntpct() function after removal in

0d651e4e "clocksource: arch_timer: use virtual counters"

We need this on certain ARMv7 systems which are architected like this:

* The firmware doesn't know and doesn't care about hypervisor mode and
we don't want to add the complexity of hypervisor there.

* The firmware isn't involved in SMP bringup or resume.

* The ARCH timer come up with an uninitialized offset between the
virtual and physical counters. Each core gets a different random

* The device boots in "Secure SVC" mode.

* Nothing has touched the reset value of CNTHCTL.PL1PCEN or
CNTHCTL.PL1PCTEN (both default to 1 at reset)

One example of such as system is RK3288 where it is much simpler to
use the physical counter since there's nobody managing the offset and
each time a core goes down and comes back up it will get reinitialized
to some other random value.

Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx>
Acked-by: Olof Johansson <olof@xxxxxxxxx>
v2: Add fixes tag to commit message, cc stable, copy Doug's
description of the systems which need this in commit message.
v3: Don't change the memory-mapped physical timer/counter code
v4: remove the memory-mapped physical counter code since it's not used
arch/arm/include/asm/arch_timer.h | 9 +++++++++
arch/arm64/include/asm/arch_timer.h | 10 ++++++++++
drivers/clocksource/arm_arch_timer.c | 10 +++++++---
3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 0704e0c..e72aa4d 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -78,6 +78,15 @@ static inline u32 arch_timer_get_cntfrq(void)
return val;

+static inline u64 arch_counter_get_cntpct(void)
+ u64 cval;
+ isb();
+ asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
+ return cval;
static inline u64 arch_counter_get_cntvct(void)
u64 cval;
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 9400596..58657c4 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -135,6 +135,16 @@ static inline void arch_timer_evtstrm_enable(int divider)

+static inline u64 arch_counter_get_cntpct(void)
+ u64 cval;
+ isb();
+ asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
+ return cval;
static inline u64 arch_counter_get_cntvct(void)
u64 cval;
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6b50311..799139f 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -429,10 +429,14 @@ static void __init arch_counter_register(unsigned type)
u64 start_count;

/* Register the CP15 based counter if we have one */
- if (type & ARCH_CP15_TIMER)
- arch_timer_read_counter = arch_counter_get_cntvct;
- else
+ if (type & ARCH_CP15_TIMER) {
+ if (arch_timer_use_virtual)
+ arch_timer_read_counter = arch_counter_get_cntvct;
+ else
+ arch_timer_read_counter = arch_counter_get_cntpct;
+ } else {
arch_timer_read_counter = arch_counter_get_cntvct_mem;
+ }

start_count = arch_timer_read_counter();
clocksource_register_hz(&clocksource_counter, arch_timer_rate);

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/