Some Cortex A9 CPU:s (e.g. zynq) have the tick tied to the CPU
frequency. On those CPU:s we cannot use the global-timer as a reliable
clocksource with CPU frequency scaling enabled since this is not
currently taken into account by the driver.
Add a "tied-to-cpu-freq" boolean to the global-timer dt node indicate
this condition.
When the global-timer register function sees this property return
immediately and don't register the clocksource.
Signed-off-by: Ola Jeppsson <ola@xxxxxxxxxxxx>
---
Documentation/devicetree/bindings/arm/global_timer.txt | 4 ++++
drivers/clocksource/arm_global_timer.c | 7 +++++++
2 files changed, 11 insertions(+)
diff --git a/Documentation/devicetree/bindings/arm/global_timer.txt b/Documentation/devicetree/bindings/arm/global_timer.txt
index bdae3a818793..465e02c17b5b 100644
--- a/Documentation/devicetree/bindings/arm/global_timer.txt
+++ b/Documentation/devicetree/bindings/arm/global_timer.txt
@@ -17,6 +17,10 @@
- clocks : Should be phandle to a clock.
+** Timer node optional properties:
+
+- tied-to-cpu-freq : indicates that the timer scales with the CPU frequency.
+
Example:
timer@2c000600 {
diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
index e6833771a716..8913ebda3f09 100644
--- a/drivers/clocksource/arm_global_timer.c
+++ b/drivers/clocksource/arm_global_timer.c
@@ -268,6 +268,13 @@ static void __init global_timer_of_register(struct device_node *np)
return;
}
+#ifdef CONFIG_CPU_FREQ
+ if (of_property_read_bool(np, "tied-to-cpu-freq")) {
+ pr_warn("global-timer: tied to cpu frequency, not supported with scaling\n");
+ return;
+ }
+#endif
+
gt_clk = of_clk_get(np, 0);
if (!IS_ERR(gt_clk)) {
err = clk_prepare_enable(gt_clk);
--
2.3.3
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