arm: arch_timer: Do not set C3STOP in case CPU_IDLE=n

Commit Message

Magnus Damm June 18, 2013, 8:16 a.m. UTC

From: Magnus Damm <[e-mail]>

Modify the ARM architected timer driver to not set C3STOP
in case CPU_IDLE is disabled. This is a short term fix that
allows use of high resolution timers even though no additional
clock event is registered.

Signed-off-by: Magnus Damm <[e-mail]>
---

 This patch is not for upstream merge nor merge into LTSI-3.4,
 instead it is expected that it will be included into the git
 repository renesas-backports at kernel.org.

 When upstream decides to merge a solution to this problem then
 this patch will be replaced with the upstream solution.

 drivers/clocksource/arm_arch_timer.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

Patch

--- 0001/drivers/clocksource/arm_arch_timer.c
+++ work/drivers/clocksource/arm_arch_timer.c	2013-06-17 09:03:44.000000000 +0900
@@ -125,7 +125,23 @@  static int arch_timer_set_next_event_phy
 
 static int __cpuinit arch_timer_setup(struct clock_event_device *clk)
 {
-	clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP;
+	clk->features = CLOCK_EVT_FEAT_ONESHOT;
+#ifdef CONFIG_CPU_IDLE
+	/* By not setting the C3STOP flag it is possible to let the
+	 * ARM architected timer to be the only clock event installed
+	 * on the system and have working high resolution timers.
+	 *
+	 * If the C3STOP flag is set unconditionally then the kernel
+	 * will always prevent using the high resoultion timer feature
+	 * unless an additional clock event is registered.
+	 *
+	 * In the case where CPU_IDLE is enabled then there is a chance
+	 * that deeper sleep states will be handled by software, but
+	 * if CPU_IDLE is disabled then deep sleep states cannot be
+	 * entered and the feature flagged by C3STOP is not needed.
+	 */
+	clk->features |= CLOCK_EVT_FEAT_C3STOP;
+#endif
 	clk->name = "arch_sys_timer";
 	clk->rating = 450;
 	if (arch_timer_use_virtual) {