clocksource/drivers/arm_arch_timer: Move system register timer programming over to CVAL

In order to cope better with high frequency counters, move the
programming of the timers from the countdown timer (TVAL) over
to the comparator (CVAL).

The programming model is slightly different, as we now need to
read the current counter value to have an absolute deadline
instead of a relative one.

There is a small overhead to this change, which we will address
in the following patches.

Reviewed-by: Oliver Upton <oupton@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211017124225.3018098-5-maz@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

1 files changed, 23 insertions, 3 deletions

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index a49bcefaa370..322165468edf 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -691,10 +691,18 @@ static __always_inline void set_next_event(const int access, unsigned long evt,
 					   struct clock_event_device *clk)
 {
 	unsigned long ctrl;
+	u64 cnt;
+
 	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
 	ctrl |= ARCH_TIMER_CTRL_ENABLE;
 	ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
-	arch_timer_reg_write(access, ARCH_TIMER_REG_TVAL, evt, clk);
+
+	if (access == ARCH_TIMER_PHYS_ACCESS)
+		cnt = __arch_counter_get_cntpct();
+	else
+		cnt = __arch_counter_get_cntvct();
+
+	arch_timer_reg_write(access, ARCH_TIMER_REG_CVAL, evt + cnt, clk);
 	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
 }
 
@@ -712,17 +720,29 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
 	return 0;
 }
 
+static __always_inline void set_next_event_mem(const int access, unsigned long evt,
+					   struct clock_event_device *clk)
+{
+	unsigned long ctrl;
+	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
+	ctrl |= ARCH_TIMER_CTRL_ENABLE;
+	ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
+
+	arch_timer_reg_write(access, ARCH_TIMER_REG_TVAL, evt, clk);
+	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
+}
+
 static int arch_timer_set_next_event_virt_mem(unsigned long evt,
 					      struct clock_event_device *clk)
 {
-	set_next_event(ARCH_TIMER_MEM_VIRT_ACCESS, evt, clk);
+	set_next_event_mem(ARCH_TIMER_MEM_VIRT_ACCESS, evt, clk);
 	return 0;
 }
 
 static int arch_timer_set_next_event_phys_mem(unsigned long evt,
 					      struct clock_event_device *clk)
 {
-	set_next_event(ARCH_TIMER_MEM_PHYS_ACCESS, evt, clk);
+	set_next_event_mem(ARCH_TIMER_MEM_PHYS_ACCESS, evt, clk);
 	return 0;
 }