arm64: kernel: implement fpsimd CPU PM notifier

When a CPU enters a low power state, its FP register content is lost.
This patch adds a notifier to save the FP context on CPU shutdown
and restore it on CPU resume. The context is saved and restored only
if the suspending thread is not a kernel thread, mirroring the current
context switch behaviour.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index bb785d23dbde..4aef42a04bdc 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -17,6 +17,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <linux/cpu_pm.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/sched.h>
@@ -113,6 +114,39 @@ EXPORT_SYMBOL(kernel_neon_end);
 
 #endif /* CONFIG_KERNEL_MODE_NEON */
 
+#ifdef CONFIG_CPU_PM
+static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
+                                  unsigned long cmd, void *v)
+{
+        switch (cmd) {
+        case CPU_PM_ENTER:
+                if (current->mm)
+                        fpsimd_save_state(&current->thread.fpsimd_state);
+                break;
+        case CPU_PM_EXIT:
+                if (current->mm)
+                        fpsimd_load_state(&current->thread.fpsimd_state);
+                break;
+        case CPU_PM_ENTER_FAILED:
+        default:
+                return NOTIFY_DONE;
+        }
+        return NOTIFY_OK;
+}
+
+static struct notifier_block fpsimd_cpu_pm_notifier_block = {
+        .notifier_call = fpsimd_cpu_pm_notifier,
+};
+
+static void fpsimd_pm_init(void)
+{
+        cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
+}
+
+#else
+static inline void fpsimd_pm_init(void) { }
+#endif /* CONFIG_CPU_PM */
+
 /*
  * FP/SIMD support code initialisation.
  */
@@ -131,6 +165,8 @@ static int __init fpsimd_init(void)
         else
                 elf_hwcap |= HWCAP_ASIMD;
 
+        fpsimd_pm_init();
+
         return 0;
 }
 late_initcall(fpsimd_init);