Subject: [RFC v2 13/18] ARM: OMAP2+: AM33XX: timer: Interchance clkevt and clksrc timers

From: [email-masked] (Jon Hunter)
Date: Thu, 17 Jan 2013 13:09:14 -0600

On 12/31/2012 07:07 AM, Vaibhav Bedia wrote:
> AM33XX has two timers (DTIMER0/1) in the WKUP domain.
> On GP devices the source of DMTIMER0 is fixed to an
> inaccurate internal 32k RC oscillator and this makes
> the DMTIMER0 practically either as a clocksource or
> as clockevent.
> 
> Currently the timer instance in WKUP domain is used
> as the clockevent and the timer in non-WKUP domain
> as the clocksource. DMTIMER1 in WKUP domain can keep
> running in suspend from a 32K clock fed from external
> OSC and can serve as the persistent clock for the kernel.
> To enable this, interchange the timers used as clocksource
> and clockevent for AM33XX.
> 
> For now a new DT property has been added to allow the timer code
> to select the timer with the right property.
> 
> It has been pointed out by Santosh Shilimkar and Kevin Hilman
> that such a change will result in soc-idle never being achieved
> on AM33XX. There are other reasons why soc-idle does not look
> feasible on AM33XX so for now we go ahead with the interchange
> of the the timers. If at a later point of time we do come up
> with an approach which makes soc-idle possible on AM33XX, this
> can be revisited.
> 
> Signed-off-by: Vaibhav Bedia <[email-masked]>
> Signed-off-by: Vaibhav Hiremath <[email-masked]>
> Cc: Tony Lingren <[email-masked]>
> Cc: Santosh Shilimkar <[email-masked]>
> Cc: Benoit Cousson <[email-masked]>
> Cc: Paul Walmsley <[email-masked]>
> Cc: Kevin Hilman <[email-masked]>
> Cc: Jon Hunter <[email-masked]>
> 
> ---
> v1->v2:
> 	Use DT properties for changing the timers
> 
>  .../devicetree/bindings/arm/omap/timer.txt         |    2 ++
>  arch/arm/boot/dts/am33xx.dtsi                      |    1 +
>  arch/arm/mach-omap2/timer.c                        |    6 +++---
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/arm/omap/timer.txt b/Documentation/devicetree/bindings/arm/omap/timer.txt
> index 8732d4d..62d4f2c 100644
> --- a/Documentation/devicetree/bindings/arm/omap/timer.txt
> +++ b/Documentation/devicetree/bindings/arm/omap/timer.txt
> @@ -18,6 +18,8 @@ Optional properties:
>  - ti,timer-pwm: 	Indicates the timer can generate a PWM output.
>  - ti,timer-secure: 	Indicates the timer is reserved on a secure OMAP device
>  			and therefore cannot be used by the kernel.
> +- ti,timer-non-wkup	Indicates the timer is in non-wkup power domain and hence
> +			will lose register context when the power domain transitions

I was hoping that we could avoid adding another property, especially
given that his equivalent to a timer that does not have the
"ti,timer-alwon" property.

>  Example:
>  
> diff --git a/arch/arm/boot/dts/am33xx.dtsi b/arch/arm/boot/dts/am33xx.dtsi
> index 4731748..b4e8bf7 100644
> --- a/arch/arm/boot/dts/am33xx.dtsi
> +++ b/arch/arm/boot/dts/am33xx.dtsi
> @@ -251,6 +251,7 @@
>  			reg = <0x48040000 0x400>;
>  			interrupts = <68>;
>  			ti,hwmods = "timer2";
> +			ti,timer-non-wkup;

Is this is only one not in the wake-up domain?

>  		};
>  
>  		timer3: timer at 48042000 {
> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
> index 38f9cbc..cfb3413 100644
> --- a/arch/arm/mach-omap2/timer.c
> +++ b/arch/arm/mach-omap2/timer.c
> @@ -264,7 +264,7 @@ static int __init omap_dm_timer_init_one(struct omap_dm_timer *timer,
>  	int r = 0;
>  
>  	if (of_have_populated_dt()) {
> -		np = omap_get_timer_dt(omap_timer_match, NULL);
> +		np = omap_get_timer_dt(omap_timer_match, property);
>  		if (!np)
>  			return -ENODEV;
>  
> @@ -633,8 +633,8 @@ OMAP_SYS_TIMER(3_gp, gptimer);
>  #endif /* CONFIG_ARCH_OMAP3 */
>  
>  #ifdef CONFIG_SOC_AM33XX
> -OMAP_SYS_GP_TIMER_INIT(3_am33xx, 1, OMAP4_MPU_SOURCE, "ti,timer-alwon",
> -		       2, OMAP4_MPU_SOURCE);
> +OMAP_SYS_GP_TIMER_INIT(3_am33xx, 2, OMAP4_MPU_SOURCE, "ti,timer-non-wkup",
> +		       1, OMAP4_MPU_SOURCE);

It seems to me here that we should specify the property "ti,timer-alwon"
for the clocksource and then no property for the clockevent. Hence, may
be the code needs to be adjusted so that if clockevent or clocksource
can use any timer (ie. no property specified), we look for a timer that
has no "ti-timer-xxxx" properties. This will ensure that if we need a
particular timer for clocksource, which we look for after clockevent, it
will be available.

Cheers
Jon