[PATCH] clocksource: arm_global_timer: Allow DT to specify already reset timer counter

[daniel.lezcano@linaro.org (Daniel Lezcano)]

On 11/25/2015 06:24 AM, Jassi Brar wrote:
> The GT counter is common to every core in a cluster. There is a usecase
> when Linux is spawned by a 'master' firmware/OS running on some core of
> the same cluster and the GT is used by the both.
>   Linux, upon boot, resetting the GT counter is obviously fatal to the
> other OS. So provide a way for DT to tell Linux if it's running in that
> 'slave' mode and must not reset the counter.
>
> Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

Hmm, I doubt that is a hardware description.

Rob ?

One comment below assuming this is acceptable.

> ---
>   Documentation/devicetree/bindings/arm/global_timer.txt |  6 ++++++
>   drivers/clocksource/arm_global_timer.c                 | 12 +++++++++---
>   2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/arm/global_timer.txt b/Documentation/devicetree/bindings/arm/global_timer.txt
> index bdae3a8..bb897a9 100644
> --- a/Documentation/devicetree/bindings/arm/global_timer.txt
> +++ b/Documentation/devicetree/bindings/arm/global_timer.txt
> @@ -17,6 +17,12 @@
>
>   - clocks : Should be phandle to a clock.
>
> +
> +** Optional properties:
> +
> +- arm,gt_no_reset : Firmware/bootloader already initialized the
> +	global timer-counter and expects it to be not reset again.
> +
>   Example:
>
>   	timer at 2c000600 {
> diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
> index a2cb6fa..952bab6 100644
> --- a/drivers/clocksource/arm_global_timer.c
> +++ b/drivers/clocksource/arm_global_timer.c
> @@ -51,6 +51,7 @@ 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_reset_counter;

Defining a global static boolean just for a check in the init function 
is ... pointless. Adding a parameter to clocksource_init would make more 
sense.

>   /*
>    * To get the value from the Global Timer Counter register proceed as follows:
> @@ -212,9 +213,11 @@ static u64 notrace gt_sched_clock_read(void)
>
>   static void __init gt_clocksource_init(void)
>   {
> -	writel(0, gt_base + GT_CONTROL);
> -	writel(0, gt_base + GT_COUNTER0);
> -	writel(0, gt_base + GT_COUNTER1);
> +	if (gt_reset_counter) {
> +		writel(0, gt_base + GT_CONTROL);
> +		writel(0, gt_base + GT_COUNTER0);
> +		writel(0, gt_base + GT_COUNTER1);
> +	}
>   	/* enables timer on all the cores */
>   	writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
>
> @@ -303,6 +306,9 @@ static void __init global_timer_of_register(struct device_node *np)
>   		goto out_irq;
>   	}
>
> +	/* See if we are told we can't reset the global timer counter */
> +	gt_reset_counter = !of_property_read_bool(np, "arm,gt_no_reset");
> +
>   	/* Immediately configure the timer on the boot CPU */
>   	gt_clocksource_init();
>   	gt_clockevents_init(this_cpu_ptr(gt_evt));
>


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