[PATCH v3] twd: Don't set CLOCK_EVT_FEAT_C3STOP unconditionally

[mark.rutland@arm.com (Mark Rutland)]

On Mon, Oct 05, 2015 at 11:50:23AM +0200, Marc Gonzalez wrote:
> In 5388a6b266 ("ARM: SMP: Always enable clock event broadcast support")
> Russell noted that "the TWD local timers are unable to wake up the CPU
> when it is placed into a low power mode".
> 
> However, some platforms do not stop the TWD block in low-power mode,
> and can thus use the TWD timers in one-shot mode, without setting up
> a broadcast device.
> 
> Make the driver check for the "twd_never_stops" property, and set the
> CLOCK_EVT_FEAT_C3STOP flag accordingly.
> 
> Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
> ---
>  Documentation/devicetree/bindings/arm/twd.txt | 5 +++++
>  arch/arm/kernel/smp_twd.c                     | 5 ++++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/arm/twd.txt b/Documentation/devicetree/bindings/arm/twd.txt
> index 75b8610939fa..7f849235e12a 100644
> --- a/Documentation/devicetree/bindings/arm/twd.txt
> +++ b/Documentation/devicetree/bindings/arm/twd.txt
> @@ -19,6 +19,11 @@ interrupts.
>  - reg : Specify the base address and the size of the TWD timer
>  	register window.
>  
> +Optional
> +- twd-never-stops : boolean property. If present, the twd driver will not set
> +  the CLOCK_EVT_FEAT_C3STOP flag. TWD timer can then operate in one-shot mode,
> +  no broadcast device required.

Please describe the actual physical details (i.e. that the TWD cannot be
placed into a state where it cannot generate interrupts) rather than
describing the Linux implementation details.

Otherwise this looks ok.

Mark.

> +
>  Example:
>  
>  	twd-timer at 2c000600 {
> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
> index e8f6d241881f..79298d4fb41f 100644
> --- a/arch/arm/kernel/smp_twd.c
> +++ b/arch/arm/kernel/smp_twd.c
> @@ -33,6 +33,7 @@ static unsigned long twd_timer_rate;
>  static DEFINE_PER_CPU(bool, percpu_setup_called);
>  
>  static struct clock_event_device __percpu *twd_evt;
> +static int feat_c3stop;
>  static int twd_ppi;
>  
>  static void twd_set_mode(enum clock_event_mode mode,
> @@ -293,7 +294,7 @@ static void twd_timer_setup(void)
>  
>  	clk->name = "local_timer";
>  	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
> -			CLOCK_EVT_FEAT_C3STOP;
> +			feat_c3stop;
>  	clk->rating = 350;
>  	clk->set_mode = twd_set_mode;
>  	clk->set_next_event = twd_set_next_event;
> @@ -345,6 +346,8 @@ static int __init twd_local_timer_common_register(struct device_node *np)
>  		goto out_irq;
>  
>  	twd_get_clock(np);
> +	if (!of_property_read_bool(np, "twd-never-stops"))
> +		feat_c3stop = CLOCK_EVT_FEAT_C3STOP;
>  
>  	/*
>  	 * Immediately configure the timer on the boot CPU, unless we need
> -- 
> 2.4.5
>