[PATCH 2/2] ARM: SH-Mobile: sh73a0: Add CPU Hotplug

[Bastian Hecht]

From: Bastian Hecht <hechtb at gmail.com>

Add the capability to add and remove CPUs on the fly.
The Cortex-A9 offers the possibility to take single cores out of the
MP Core. We add this capabilty taking care that caches are kept
coherent. For the actual shutdown via a WFI instruction, a code snippet
from the omap2 code tree is copied. Thanks for that! For verifying the
shutdown we rely on the internal SH73A0 Power Status Register
PSTR.

Signed-off-by: Bastian Hecht <hechtb+renesas at gmail.com>
---
 arch/arm/mach-shmobile/headsmp-sh73a0.S      |   46 ++++++++++++++++++++++++++
 arch/arm/mach-shmobile/include/mach/common.h |    1 +
 arch/arm/mach-shmobile/smp-sh73a0.c          |   41 +++++++++++++++++++----
 3 files changed, 82 insertions(+), 6 deletions(-)

diff --git a/arch/arm/mach-shmobile/headsmp-sh73a0.S b/arch/arm/mach-shmobile/headsmp-sh73a0.S
index bec4c0d..be463a3 100644
--- a/arch/arm/mach-shmobile/headsmp-sh73a0.S
+++ b/arch/arm/mach-shmobile/headsmp-sh73a0.S
@@ -23,6 +23,52 @@
 #include <linux/init.h>
 #include <asm/memory.h>
 
+/* Taken from arch/arm/mach-omap2/sleep44xx.S. Thanks! */
+ENTRY(sh73a0_do_wfi)
+        stmfd   sp!, {lr}
+
+        /*
+         * Execute an ISB instruction to ensure that all of the
+         * CP15 register changes have been committed.
+         */
+        isb
+
+        /*
+         * Execute a barrier instruction to ensure that all cache,
+         * TLB and branch predictor maintenance operations issued
+         * by any CPU in the cluster have completed.
+         */
+        dsb
+        dmb
+
+        /*
+         * Execute a WFI instruction and wait until the
+         * STANDBYWFI output is asserted to indicate that the
+         * CPU is in idle and low power state. CPU can specualatively
+         * prefetch the instructions so add NOPs after WFI. Sixteen
+         * NOPs as per Cortex-A9 pipeline.
+         */
+        wfi                                     @ Wait For Interrupt
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+        nop
+
+        ldmfd   sp!, {pc}
+ENDPROC(sh73a0_do_wfi)
+
 	__CPUINIT
 /*
  * Reset vector for secondary CPUs.
diff --git a/arch/arm/mach-shmobile/include/mach/common.h b/arch/arm/mach-shmobile/include/mach/common.h
index f2e2c29..40f767e 100644
--- a/arch/arm/mach-shmobile/include/mach/common.h
+++ b/arch/arm/mach-shmobile/include/mach/common.h
@@ -55,6 +55,7 @@ extern void sh73a0_add_standard_devices(void);
 extern void sh73a0_clock_init(void);
 extern void sh73a0_pinmux_init(void);
 extern void sh73a0_secondary_vector(void);
+extern void sh73a0_do_wfi(void);
 extern struct clk sh73a0_extal1_clk;
 extern struct clk sh73a0_extal2_clk;
 extern struct clk sh73a0_extcki_clk;
diff --git a/arch/arm/mach-shmobile/smp-sh73a0.c b/arch/arm/mach-shmobile/smp-sh73a0.c
index 5e36f5d..9237e13 100644
--- a/arch/arm/mach-shmobile/smp-sh73a0.c
+++ b/arch/arm/mach-shmobile/smp-sh73a0.c
@@ -24,6 +24,7 @@
 #include <linux/io.h>
 #include <linux/delay.h>
 #include <mach/common.h>
+#include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 #include <mach/sh73a0.h>
 #include <asm/smp_scu.h>
@@ -36,6 +37,8 @@
 #define SBAR		IOMEM(0xe6180020)
 #define APARMBAREA	IOMEM(0xe6f10020)
 
+#define PSTR_SHUTDOWN_MODE	3
+
 static void __iomem *scu_base_addr(void)
 {
 	return (void __iomem *)0xf0000000;
@@ -92,16 +95,20 @@ static void __init sh73a0_smp_init_cpus(void)
 	shmobile_smp_init_cpus(ncores);
 }
 
-static int __maybe_unused sh73a0_cpu_kill(unsigned int cpu)
+#ifdef CONFIG_HOTPLUG_CPU
+static int sh73a0_cpu_kill(unsigned int cpu)
 {
+
 	int k;
+	u32 pstr;
 
-	/* this function is running on another CPU than the offline target,
-	 * here we need wait for shutdown code in platform_cpu_die() to
-	 * finish before asking SoC-specific code to power off the CPU core.
+	/*
+	 * wait until the power status register confirms the shutdown of the
+	 * offline target
 	 */
 	for (k = 0; k < 1000; k++) {
-		if (shmobile_cpu_is_dead(cpu))
+		pstr = (__raw_readl(PSTR) >> (4 * cpu)) & 3;
+		if (pstr == PSTR_SHUTDOWN_MODE)
 			return 1;
 
 		mdelay(1);
@@ -110,6 +117,28 @@ static int __maybe_unused sh73a0_cpu_kill(unsigned int cpu)
 	return 0;
 }
 
+static void sh73a0_cpu_die(unsigned int cpu)
+{
+	/*
+	 * The ARM MPcore does not issue a cache coherency request for the L1
+	 * cache when powering off single CPUs. We must take care of this and
+	 * further caches.
+	 */
+	dsb();
+	flush_cache_all();
+
+	/* Set power off mode. This takes the CPU out of the MP cluster */
+	scu_power_mode(scu_base_addr(), SCU_PM_POWEROFF);
+
+	/* Enter shutdown mode */
+	sh73a0_do_wfi();
+
+	/* We assume success always. We never reach this */
+	pr_err("Shutting down CPU failed. This should never happen!\n");
+	for (;;)
+		;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
 
 struct smp_operations sh73a0_smp_ops __initdata = {
 	.smp_init_cpus		= sh73a0_smp_init_cpus,
@@ -118,7 +147,7 @@ struct smp_operations sh73a0_smp_ops __initdata = {
 	.smp_boot_secondary	= sh73a0_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_kill		= sh73a0_cpu_kill,
-	.cpu_die		= shmobile_cpu_die,
+	.cpu_die		= sh73a0_cpu_die,
 	.cpu_disable		= shmobile_cpu_disable,
 #endif
 };
-- 
1.7.9.5