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>
Conflicts:
	arch/arm64/kernel/fpsimd.c

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 2fa308e4a1fad61448971f69be317249fb1c87b5..522df9c7f3a4288cf5c8e5bb07f564304bd6ab15 100644 (file)
--- 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>
@@ -85,6 +86,66 @@ void fpsimd_flush_thread(void)
        preempt_enable();
 }
 
+#ifdef CONFIG_KERNEL_MODE_NEON
+
+/*
+ * Kernel-side NEON support functions
+ */
+void kernel_neon_begin(void)
+{
+       /* Avoid using the NEON in interrupt context */
+       BUG_ON(in_interrupt());
+       preempt_disable();
+
+       if (current->mm)
+               fpsimd_save_state(&current->thread.fpsimd_state);
+}
+EXPORT_SYMBOL(kernel_neon_begin);
+
+void kernel_neon_end(void)
+{
+       if (current->mm)
+               fpsimd_load_state(&current->thread.fpsimd_state);
+
+       preempt_enable();
+}
+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.
  */
@@ -103,6 +164,8 @@ static int __init fpsimd_init(void)
        else
                elf_hwcap |= HWCAP_ASIMD;
 
+       fpsimd_pm_init();
+
        return 0;
 }
 late_initcall(fpsimd_init);