[PATCH] ARM: imx: disable cpu in .cpu_kill hook

[Shawn Guo]

It's buggy to disable the cpu that is being hot-unplugged in .cpu_die
hook which runs on the cpu itself.  Instead, it should be done in
.cpu_kill which runs on the thread (another cpu) that asks for shutting
down the cpu.  Move imx_enable_cpu(cpu, false) call into .cpu_kill
hook, and leave the cpu to be hot-unplugged in WFI with a recovery call
cpu_leave_lowpower(), so that we can get a more stable cpu hot-plug
operation.

Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
---
 arch/arm/mach-imx/common.h  |    1 +
 arch/arm/mach-imx/hotplug.c |   31 +++++++++++++++++++++++++++----
 arch/arm/mach-imx/platsmp.c |    1 +
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mach-imx/common.h b/arch/arm/mach-imx/common.h
index 7191ab4..fa36fb8 100644
--- a/arch/arm/mach-imx/common.h
+++ b/arch/arm/mach-imx/common.h
@@ -142,6 +142,7 @@ extern int imx6q_set_lpm(enum mxc_cpu_pwr_mode mode);
 extern void imx6q_clock_map_io(void);
 
 extern void imx_cpu_die(unsigned int cpu);
+extern int imx_cpu_kill(unsigned int cpu);
 
 #ifdef CONFIG_PM
 extern void imx6q_pm_init(void);
diff --git a/arch/arm/mach-imx/hotplug.c b/arch/arm/mach-imx/hotplug.c
index 3dec962..a9b4096 100644
--- a/arch/arm/mach-imx/hotplug.c
+++ b/arch/arm/mach-imx/hotplug.c
@@ -38,6 +38,22 @@ static inline void cpu_enter_lowpower(void)
 	  : "cc");
 }
 
+static inline void cpu_leave_lowpower(void)
+{
+	unsigned int v;
+
+	asm volatile(
+		"mrc	p15, 0, %0, c1, c0, 0\n"
+	"	orr	%0, %0, %1\n"
+	"	mcr	p15, 0, %0, c1, c0, 0\n"
+	"	mrc	p15, 0, %0, c1, c0, 1\n"
+	"	orr	%0, %0, %2\n"
+	"	mcr	p15, 0, %0, c1, c0, 1\n"
+	  : "=&r" (v)
+	  : "Ir" (CR_C), "Ir" (0x40)
+	  : "cc");
+}
+
 /*
  * platform-specific code to shutdown a CPU
  *
@@ -45,10 +61,17 @@ static inline void cpu_enter_lowpower(void)
  */
 void imx_cpu_die(unsigned int cpu)
 {
+	static int spurious;
+
 	cpu_enter_lowpower();
-	imx_enable_cpu(cpu, false);
+	cpu_do_idle();
+	cpu_leave_lowpower();
 
-	/* spin here until hardware takes it down */
-	while (1)
-		;
+	pr_warn("CPU%u: %u spurious wakeup calls\n", cpu, ++spurious);
+}
+
+int imx_cpu_kill(unsigned int cpu)
+{
+	imx_enable_cpu(cpu, false);
+	return 1;
 }
diff --git a/arch/arm/mach-imx/platsmp.c b/arch/arm/mach-imx/platsmp.c
index 3777b80..66fae88 100644
--- a/arch/arm/mach-imx/platsmp.c
+++ b/arch/arm/mach-imx/platsmp.c
@@ -92,5 +92,6 @@ struct smp_operations  imx_smp_ops __initdata = {
 	.smp_boot_secondary	= imx_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_die		= imx_cpu_die,
+	.cpu_kill		= imx_cpu_kill,
 #endif
 };
-- 
1.7.9.5