ARM: VFP: re-initialize VFP coprocessor access enables on CPU hotplug

We can not guarantee that VFP will be enabled when CPU hotplug brings
a CPU back online from a reset state.  Add a hotplug CPU notifier to
ensure that the VFP coprocessor access is enabled whenever a CPU comes
back online.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 23 insertions, 1 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 8063a322c790..0797cb528b46 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -10,9 +10,12 @@
  */
 #include <linux/module.h>
 #include <linux/types.h>
+#include <linux/cpu.h>
 #include <linux/kernel.h>
+#include <linux/notifier.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
+#include <linux/smp.h>
 #include <linux/init.h>
 
 #include <asm/cputype.h>
@@ -484,7 +487,24 @@ void vfp_flush_hwstate(struct thread_info *thread)
         put_cpu();
 }
 
-#include <linux/smp.h>
+/*
+ * VFP hardware can lose all context when a CPU goes offline.
+ * Safely clear our held state when a CPU has been killed, and
+ * re-enable access to VFP when the CPU comes back online.
+ *
+ * Both CPU_DYING and CPU_STARTING are called on the CPU which
+ * is being offlined/onlined.
+ */
+static int vfp_hotplug(struct notifier_block *b, unsigned long action,
+        void *hcpu)
+{
+        if (action == CPU_DYING || action == CPU_DYING_FROZEN) {
+                unsigned int cpu = (long)hcpu;
+                last_VFP_context[cpu] = NULL;
+        } else if (action == CPU_STARTING || action == CPU_STARTING_FROZEN)
+                vfp_enable(NULL);
+        return NOTIFY_OK;
+}
 
 /*
  * VFP support code initialisation.
@@ -514,6 +534,8 @@ static int __init vfp_init(void)
         else if (vfpsid & FPSID_NODOUBLE) {
                 printk("no double precision support\n");
         } else {
+                hotcpu_notifier(vfp_hotplug, 0);
+
                 smp_call_function(vfp_enable, NULL, 1);
 
                 VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;  /* Extract the architecture version */