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authorLorenzo Pieralisi <lorenzo.pieralisi@arm.com>2013-07-22 15:22:13 +0400
committerLorenzo Pieralisi <lorenzo.pieralisi@arm.com>2013-12-16 21:17:31 +0400
commit95322526ef62b84adb469c27535ab0252a369a85 (patch)
tree81fe36a9dd3361ebbcfbebee7a18207c0f58b7f9 /arch/arm64/kernel/suspend.c
parent6732bc65c277b697f6d8b645b15f63d1558c0cc4 (diff)
downloadlinux-95322526ef62b84adb469c27535ab0252a369a85.tar.xz
arm64: kernel: cpu_{suspend/resume} implementation
Kernel subsystems like CPU idle and suspend to RAM require a generic mechanism to suspend a processor, save its context and put it into a quiescent state. The cpu_{suspend}/{resume} implementation provides such a framework through a kernel interface allowing to save/restore registers, flush the context to DRAM and suspend/resume to/from low-power states where processor context may be lost. The CPU suspend implementation relies on the suspend protocol registered in CPU operations to carry out a suspend request after context is saved and flushed to DRAM. The cpu_suspend interface: int cpu_suspend(unsigned long arg); allows to pass an opaque parameter that is handed over to the suspend CPU operations back-end so that it can take action according to the semantics attached to it. The arg parameter allows suspend to RAM and CPU idle drivers to communicate to suspend protocol back-ends; it requires standardization so that the interface can be reused seamlessly across systems, paving the way for generic drivers. Context memory is allocated on the stack, whose address is stashed in a per-cpu variable to keep track of it and passed to core functions that save/restore the registers required by the architecture. Even though, upon successful execution, the cpu_suspend function shuts down the suspending processor, the warm boot resume mechanism, based on the cpu_resume function, makes the resume path operate as a cpu_suspend function return, so that cpu_suspend can be treated as a C function by the caller, which simplifies coding the PM drivers that rely on the cpu_suspend API. Upon context save, the minimal amount of memory is flushed to DRAM so that it can be retrieved when the MMU is off and caches are not searched. The suspend CPU operation, depending on the required operations (eg CPU vs Cluster shutdown) is in charge of flushing the cache hierarchy either implicitly (by calling firmware implementations like PSCI) or explicitly by executing the required cache maintainance functions. Debug exceptions are disabled during cpu_{suspend}/{resume} operations so that debug registers can be saved and restored properly preventing preemption from debug agents enabled in the kernel. Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Diffstat (limited to 'arch/arm64/kernel/suspend.c')
-rw-r--r--arch/arm64/kernel/suspend.c109
1 files changed, 109 insertions, 0 deletions
diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
new file mode 100644
index 000000000000..e074b1c32723
--- /dev/null
+++ b/arch/arm64/kernel/suspend.c
@@ -0,0 +1,109 @@
+#include <linux/slab.h>
+#include <asm/cacheflush.h>
+#include <asm/cpu_ops.h>
+#include <asm/debug-monitors.h>
+#include <asm/pgtable.h>
+#include <asm/memory.h>
+#include <asm/smp_plat.h>
+#include <asm/suspend.h>
+#include <asm/tlbflush.h>
+
+extern int __cpu_suspend(unsigned long);
+/*
+ * This is called by __cpu_suspend() to save the state, and do whatever
+ * flushing is required to ensure that when the CPU goes to sleep we have
+ * the necessary data available when the caches are not searched.
+ *
+ * @arg: Argument to pass to suspend operations
+ * @ptr: CPU context virtual address
+ * @save_ptr: address of the location where the context physical address
+ * must be saved
+ */
+int __cpu_suspend_finisher(unsigned long arg, struct cpu_suspend_ctx *ptr,
+ phys_addr_t *save_ptr)
+{
+ int cpu = smp_processor_id();
+
+ *save_ptr = virt_to_phys(ptr);
+
+ cpu_do_suspend(ptr);
+ /*
+ * Only flush the context that must be retrieved with the MMU
+ * off. VA primitives ensure the flush is applied to all
+ * cache levels so context is pushed to DRAM.
+ */
+ __flush_dcache_area(ptr, sizeof(*ptr));
+ __flush_dcache_area(save_ptr, sizeof(*save_ptr));
+
+ return cpu_ops[cpu]->cpu_suspend(arg);
+}
+
+/**
+ * cpu_suspend
+ *
+ * @arg: argument to pass to the finisher function
+ */
+int cpu_suspend(unsigned long arg)
+{
+ struct mm_struct *mm = current->active_mm;
+ int ret, cpu = smp_processor_id();
+ unsigned long flags;
+
+ /*
+ * If cpu_ops have not been registered or suspend
+ * has not been initialized, cpu_suspend call fails early.
+ */
+ if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_suspend)
+ return -EOPNOTSUPP;
+
+ /*
+ * From this point debug exceptions are disabled to prevent
+ * updates to mdscr register (saved and restored along with
+ * general purpose registers) from kernel debuggers.
+ */
+ local_dbg_save(flags);
+
+ /*
+ * mm context saved on the stack, it will be restored when
+ * the cpu comes out of reset through the identity mapped
+ * page tables, so that the thread address space is properly
+ * set-up on function return.
+ */
+ ret = __cpu_suspend(arg);
+ if (ret == 0) {
+ cpu_switch_mm(mm->pgd, mm);
+ flush_tlb_all();
+ }
+
+ /*
+ * Restore pstate flags. OS lock and mdscr have been already
+ * restored, so from this point onwards, debugging is fully
+ * renabled if it was enabled when core started shutdown.
+ */
+ local_dbg_restore(flags);
+
+ return ret;
+}
+
+extern struct sleep_save_sp sleep_save_sp;
+extern phys_addr_t sleep_idmap_phys;
+
+static int cpu_suspend_init(void)
+{
+ void *ctx_ptr;
+
+ /* ctx_ptr is an array of physical addresses */
+ ctx_ptr = kcalloc(mpidr_hash_size(), sizeof(phys_addr_t), GFP_KERNEL);
+
+ if (WARN_ON(!ctx_ptr))
+ return -ENOMEM;
+
+ sleep_save_sp.save_ptr_stash = ctx_ptr;
+ sleep_save_sp.save_ptr_stash_phys = virt_to_phys(ctx_ptr);
+ sleep_idmap_phys = virt_to_phys(idmap_pg_dir);
+ __flush_dcache_area(&sleep_save_sp, sizeof(struct sleep_save_sp));
+ __flush_dcache_area(&sleep_idmap_phys, sizeof(sleep_idmap_phys));
+
+ return 0;
+}
+early_initcall(cpu_suspend_init);