Hi Srini, Ola,
On 04/14/2015 09:41 AM, Srinivas Kandagatla wrote:
+Adding Pete and Maxime
Hi Ola,
Thankyou for sending the patch,
I like the Idea, but I have some specific concerns which would break
existing SOCs.
I like the idea too.
On 13/04/15 18:37, Ola Jeppsson wrote:
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
+
This patch would not let the SOC like STiH415/416 or zynq with
"tied-to-cpu-freq" property to boot with multi_v7_defconfig. Which is
not correct thing to do, as STi SOC's do not use cpufreq driver
however the tick is tied to this clocksource.
Yes, you are right, but I don't see any cleaner way to do this.
On STi, we have another timer we can use as a clocksource when doing CPU
Freq, the ST LPC timer.
It is not upstreamed yet, but we will try to have it for next release.
I propose we set the "tied-to-cpu-freq" in GT node of STi family as soon
as we enable the LPC timer one.
Doing that, the STi boot won't break in multi_v7 config.
Kind regards,
Maxime
--srini
gt_clk = of_clk_get(np, 0);
if (!IS_ERR(gt_clk)) {
err = clk_prepare_enable(gt_clk);
--
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