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

[Shawn Guo]

From: Mike Turquette <mturquette at linaro.org>

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 the existing code to use clk notifiers
in place of CPUfreq notifiers.  This works out nicely for Cortex-A9
MPcore designs that scale all CPUs at the same frequency.

Signed-off-by: Mike Turquette <mturquette at linaro.org>
Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
---
 arch/arm/kernel/smp_twd.c |   32 +++++++++++++-------------------
 1 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index fef42b2..635e3ea 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>
@@ -96,51 +95,46 @@ static void twd_timer_stop(struct clock_event_device *clk)
 	disable_percpu_irq(clk->irq);
 }
 
-#ifdef CONFIG_CPU_FREQ
-
 /*
  * 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 *data)
+static void twd_update_frequency(void *new_rate)
 {
-	twd_timer_rate = clk_get_rate(twd_clk);
+	twd_timer_rate = *((unsigned long *) new_rate);
 
 	clockevents_update_freq(*__this_cpu_ptr(twd_evt), twd_timer_rate);
 }
 
-static int twd_cpufreq_transition(struct notifier_block *nb,
-	unsigned long state, void *data)
+static int twd_rate_change(struct notifier_block *nb,
+	unsigned long flags, void *data)
 {
-	struct cpufreq_freqs *freqs = 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 (state == CPUFREQ_POSTCHANGE || state == CPUFREQ_RESUMECHANGE)
-		smp_call_function_single(freqs->cpu, twd_update_frequency,
-			NULL, 1);
+	if (flags == POST_RATE_CHANGE)
+		smp_call_function(twd_update_frequency,
+				  (void *)&cnd->new_rate, 1);
 
 	return NOTIFY_OK;
 }
 
-static struct notifier_block twd_cpufreq_nb = {
-	.notifier_call = twd_cpufreq_transition,
+static struct notifier_block twd_clk_nb = {
+	.notifier_call = twd_rate_change,
 };
 
-static int twd_cpufreq_init(void)
+static int twd_clk_init(void)
 {
 	if (twd_evt && *__this_cpu_ptr(twd_evt) && !IS_ERR(twd_clk))
-		return cpufreq_register_notifier(&twd_cpufreq_nb,
-			CPUFREQ_TRANSITION_NOTIFIER);
+		return clk_notifier_register(twd_clk, &twd_clk_nb);
 
 	return 0;
 }
-core_initcall(twd_cpufreq_init);
-
-#endif
+core_initcall(twd_clk_init);
 
 static void __cpuinit twd_calibrate_rate(void)
 {
-- 
1.7.5.4