[PATCH v2] ARM: smp_twd: reprogram twd based on clk notifier

[Mike Turquette]

Running cpufreq driver on imx6q, the following warning is seen.

$ BUG: sleeping function called from invalid context at kernel/mutex.c:269

<snip>

stack backtrace:
Backtrace:
[<80011d64>] (dump_backtrace+0x0/0x10c) from [<803fc164>] (dump_stack+0x18/0x1c)
 r6:bf8142e0 r5:bf814000 r4:806ac794 r3:bf814000
[<803fc14c>] (dump_stack+0x0/0x1c) from [<803fd444>] (print_usage_bug+0x250/0x2b
8)
[<803fd1f4>] (print_usage_bug+0x0/0x2b8) from [<80060f90>] (mark_lock+0x56c/0x67
0)
[<80060a24>] (mark_lock+0x0/0x670) from [<80061a20>] (__lock_acquire+0x98c/0x19b
4)
[<80061094>] (__lock_acquire+0x0/0x19b4) from [<80062f14>] (lock_acquire+0x68/0x
7c)
[<80062eac>] (lock_acquire+0x0/0x7c) from [<80400f28>] (mutex_lock_nested+0x78/0
x344)
 r7:00000000 r6:bf872000 r5:805cc858 r4:805c2a04
[<80400eb0>] (mutex_lock_nested+0x0/0x344) from [<803089ac>] (clk_get_rate+0x1c/
0x58)
[<80308990>] (clk_get_rate+0x0/0x58) from [<80013c48>] (twd_update_frequency+0x1
8/0x50)
 r5:bf253d04 r4:805cadf4
[<80013c30>] (twd_update_frequency+0x0/0x50) from [<80068e20>] (generic_smp_call
_function_single_interrupt+0xd4/0x13c)
 r4:bf873ee0 r3:80013c30
[<80068d4c>] (generic_smp_call_function_single_interrupt+0x0/0x13c) from [<80013
34c>] (handle_IPI+0xc0/0x194)
 r8:00000001 r7:00000000 r6:80574e48 r5:bf872000 r4:80593958
[<8001328c>] (handle_IPI+0x0/0x194) from [<800084e8>] (gic_handle_irq+0x58/0x60)
 r8:00000000 r7:bf873f8c r6:bf873f58 r5:80593070 r4:f4000100
r3:00000005
[<80008490>] (gic_handle_irq+0x0/0x60) from [<8000e124>] (__irq_svc+0x44/0x60)
Exception stack(0xbf873f58 to 0xbf873fa0)
3f40:                                                       00000001 00000001
3f60: 00000000 bf814000 bf872000 805cab48 80405aa4 80597648 00000000 412fc09a
3f80: bf872000 bf873fac bf873f70 bf873fa0 80063844 8000f1f8 20000013 ffffffff
 r6:ffffffff r5:20000013 r4:8000f1f8 r3:bf814000
[<8000f1b8>] (default_idle+0x0/0x4c) from [<8000f428>] (cpu_idle+0x98/0x114)
[<8000f390>] (cpu_idle+0x0/0x114) from [<803f9834>] (secondary_start_kernel+0x11
c/0x140)
[<803f9718>] (secondary_start_kernel+0x0/0x140) from [<103f9234>] (0x103f9234)
 r6:10c03c7d r5:0000001f r4:4f86806a r3:803f921c

It looks that the warning is caused by that twd_update_frequency() gets
called from an atomic context while it calls clk_get_rate() where a
mutex gets held.

To fix the warning, let's convert common clk users over to clk notifiers
in place of CPUfreq notifiers.  This works out nicely for Cortex-A9
MPcore designs that scale all CPUs at the same frequency.

Platforms that have not been converted to the common clk framework and
support CPUfreq will rely on the old mechanism.  Once these platforms
are converted over fully then we can remove the CPUfreq-specific bits
for good.

Signed-off-by: Mike Turquette <mturquette at linaro.org>
Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
---
Changes in v2:
 * Kept the original CPUfreq notifier scheme in place for platforms that
   have not adapted to the common clk framework yet

Testing notes:
 * Tested on OMAP4430 Panda against v3.6-rc5 with legacy clk framework
   and with local common clk patches, thus both code paths are validated
 * CPUfreq userspace governor @ 300MHz, 600MHz and 1008MHz
 * Ran "date; sleep 30; date" and compared with a stopwatch to verify
   correct timekeeping

 arch/arm/kernel/smp_twd.c |   48 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index fef42b2..e1f9069 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -11,7 +11,6 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/clk.h>
-#include <linux/cpufreq.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/err.h>
@@ -96,7 +95,52 @@ static void twd_timer_stop(struct clock_event_device *clk)
 	disable_percpu_irq(clk->irq);
 }
 
-#ifdef CONFIG_CPU_FREQ
+#ifdef CONFIG_COMMON_CLK
+
+/*
+ * Updates clockevent frequency when the cpu frequency changes.
+ * Called on the cpu that is changing frequency with interrupts disabled.
+ */
+static void twd_update_frequency(void *new_rate)
+{
+	twd_timer_rate = *((unsigned long *) new_rate);
+
+	clockevents_update_freq(*__this_cpu_ptr(twd_evt), twd_timer_rate);
+}
+
+static int twd_rate_change(struct notifier_block *nb,
+	unsigned long flags, void *data)
+{
+	struct clk_notifier_data *cnd = data;
+
+	/*
+	 * The twd clock events must be reprogrammed to account for the new
+	 * frequency.  The timer is local to a cpu, so cross-call to the
+	 * changing cpu.
+	 */
+	if (flags == POST_RATE_CHANGE)
+		smp_call_function(twd_update_frequency,
+				  (void *)&cnd->new_rate, 1);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block twd_clk_nb = {
+	.notifier_call = twd_rate_change,
+};
+
+static int twd_clk_init(void)
+{
+	if (twd_evt && *__this_cpu_ptr(twd_evt) && !IS_ERR(twd_clk))
+		return clk_notifier_register(twd_clk, &twd_clk_nb);
+
+	return 0;
+}
+core_initcall(twd_clk_init);
+
+#elif defined (CONFIG_CPU_FREQ)
+
+#include <linux/cpufreq.h>
 
 /*
  * Updates clockevent frequency when the cpu frequency changes.
-- 
1.7.9.5