MIPS: PM: Add CPU PM callbacks for general CPU context

Add a CPU power management notifier callback for preserving general CPU
context. The CPU PM callbacks will be triggered by the powering down of
CPU cores, for example by cpuidle drivers & in the future by suspend to
RAM implementations.

The current state preserved is mostly related to the process context:
- FPU
- DSP
- ASID
- UserLocal
- Watch registers

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Paul Burton <paul.burton@imgtec.com>

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 5cd695f..322bbe1 100644 (file)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -50,6 +50,7 @@ config MIPS
        select CLONE_BACKWARDS
        select HAVE_DEBUG_STACKOVERFLOW
        select HAVE_CC_STACKPROTECTOR
+       select CPU_PM if CPU_IDLE
 
 menu "Machine selection"
 

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 277dab3..97540a8 100644 (file)
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -107,6 +107,8 @@ obj-$(CONFIG_JUMP_LABEL)    += jump_label.o
 obj-$(CONFIG_MIPS_CM)          += mips-cm.o
 obj-$(CONFIG_MIPS_CPC)         += mips-cpc.o
 
+obj-$(CONFIG_CPU_PM)           += pm.o
+
 #
 # DSP ASE supported for MIPS32 or MIPS64 Release 2 cores only. It is not
 # safe to unconditionnaly use the assembler -mdsp / -mdspr2 switches

diff --git a/arch/mips/kernel/pm.c b/arch/mips/kernel/pm.c
new file mode 100644 (file)
index 0000000..112903f
--- /dev/null
+++ b/arch/mips/kernel/pm.c
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2014 Imagination Technologies Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under  the terms of the GNU General  Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ *
+ * CPU PM notifiers for saving/restoring general CPU state.
+ */
+
+#include <linux/cpu_pm.h>
+#include <linux/init.h>
+
+#include <asm/dsp.h>
+#include <asm/fpu.h>
+#include <asm/mmu_context.h>
+#include <asm/watch.h>
+
+/**
+ * mips_cpu_save() - Save general CPU state.
+ * Ensures that general CPU context is saved, notably FPU and DSP.
+ */
+static int mips_cpu_save(void)
+{
+       /* Save FPU state */
+       lose_fpu(1);
+
+       /* Save DSP state */
+       save_dsp(current);
+
+       return 0;
+}
+
+/**
+ * mips_cpu_restore() - Restore general CPU state.
+ * Restores important CPU context.
+ */
+static void mips_cpu_restore(void)
+{
+       unsigned int cpu = smp_processor_id();
+
+       /* Restore ASID */
+       if (current->mm)
+               write_c0_entryhi(cpu_asid(cpu, current->mm));
+
+       /* Restore DSP state */
+       restore_dsp(current);
+
+       /* Restore UserLocal */
+       if (cpu_has_userlocal)
+               write_c0_userlocal(current_thread_info()->tp_value);
+
+       /* Restore watch registers */
+       __restore_watch();
+}
+
+/**
+ * mips_pm_notifier() - Notifier for preserving general CPU context.
+ * @self:      Notifier block.
+ * @cmd:       CPU PM event.
+ * @v:         Private data (unused).
+ *
+ * This is called when a CPU power management event occurs, and is used to
+ * ensure that important CPU context is preserved across a CPU power down.
+ */
+static int mips_pm_notifier(struct notifier_block *self, unsigned long cmd,
+                           void *v)
+{
+       int ret;
+
+       switch (cmd) {
+       case CPU_PM_ENTER:
+               ret = mips_cpu_save();
+               if (ret)
+                       return NOTIFY_STOP;
+               break;
+       case CPU_PM_ENTER_FAILED:
+       case CPU_PM_EXIT:
+               mips_cpu_restore();
+               break;
+       }
+
+       return NOTIFY_OK;
+}
+
+static struct notifier_block mips_pm_notifier_block = {
+       .notifier_call = mips_pm_notifier,
+};
+
+static int __init mips_pm_init(void)
+{
+       return cpu_pm_register_notifier(&mips_pm_notifier_block);
+}
+arch_initcall(mips_pm_init);