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

From: [email-masked] (Marc Gonzalez)
Date: Mon, 5 Oct 2015 11:50:23 +0200

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 <[email-masked]>
---
 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.
+
 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