[PATCH] clocksource: arm_global_timer: Detect if gt is usable with CPU_FREQ

[Sören Brinkmann]

On Tue, 2015-04-14 at 08:41AM +0100, 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.
> 
> 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 at adapteva.com>
> >---
> >  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 at 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.

For Zynq, it should be OK, since we have the cadence_ttc as alternative
clocksource. Though, I have to admit not having tested this patch.

	Sören