Re: [PATCH] clocksource: arm_global_timer: fix suspend resume

From: Grygorii Strashko
Date: Fri Nov 13 2015 - 13:30:33 EST

On 11/13/2015 08:15 PM, Felipe Balbi wrote:


Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
On 11/13/2015 07:40 PM, Felipe Balbi wrote:


Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
On 11/13/2015 06:43 PM, Felipe Balbi wrote:


Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
Now the System stall is observed on TI AM437x based board
(am437x-gp-evm) during resuming from System suspend when ARM Global
timer is selected as clocksource device - SysRq are working, but
nothing else. The reason of stall is that ARM Global timer loses its

The reason of stall is that ARM Global timer loses its contexts during
System suspend:

Hence, update ARM Global timer driver to reflect above behaviour
- save GT_CONTROL.TIMER_ENABLE during suspend and restore on resume;
- ensure clocksource and clockevent devices have coresponding flags
depending on presence of "always-on" DT property.

CC: Arnd Bergmann <arnd@xxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Felipe Balbi <balbi@xxxxxx>
Cc: Tony Lindgren <tony@xxxxxxxxxxx>
Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
drivers/clocksource/arm_global_timer.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
index a2cb6fa..1bbaf64 100644
--- a/drivers/clocksource/arm_global_timer.c
+++ b/drivers/clocksource/arm_global_timer.c
@@ -51,6 +51,8 @@ static void __iomem *gt_base;
static unsigned long gt_clk_rate;
static int gt_ppi;
static struct clock_event_device __percpu *gt_evt;
+static bool gt_always_on;
+static u32 gt_control;

* To get the value from the Global Timer Counter register proceed as follows:
@@ -168,6 +170,9 @@ static int gt_clockevents_init(struct clock_event_device *clk)
int cpu = smp_processor_id();

+ if (!gt_always_on)
+ clk->features |= CLOCK_EVT_FEAT_C3STOP;
clk->name = "arm_global_timer";
@@ -195,12 +200,25 @@ static cycle_t gt_clocksource_read(struct clocksource *cs)
return gt_counter_read();

+static void gt_suspend(struct clocksource *cs)
+ gt_control = readl(gt_base + GT_CONTROL);
+static void gt_resume(struct clocksource *cs)
+ /* enables timer on all the cores */
+ writel(gt_control & GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);

do you really need to save context if all you restore is TIMER_ENABLE
bit ? seems like you could skip gt_suspend altogether. Is there really a
situation where this driver is running and GT isn't enabled ?

Now It's not. It's always enabled. I did it because .suspend() is called for
all registered clock sources regardless of their usage. So, potentially
in the future, at the moment when .suspend() is called it might be disabled
(for example, .enable/disable() callbacks can be added and, if ARM Global timer
will not be registered as sched_clock, it will be possible to keep it disabled
if not used now).

But It's not essentially now - I can update it and drop save restore.
Pls, confirm.

I think it's best to skip suspend completely. You're not restoring
anything you saved during suspend, unless you meant | where you used &.

I didn't get it - I'm restoring one bit(0) only.

that's the point, if you know you're restoring only that bit. Why save
anything at all ?

i think there are difference between "restoring" and "re-enabling".
"restoring" - assume saving smth.. then restore saving value.
I'm saving & restoring one bit here.

But I can do just "re-enabling" -
and then I don't need to save anything. It will work with current

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