[ARM] Add thread_notify infrastructure

Some machine classes need to allow VFP support to be built into the
kernel, but still allow the kernel to run even though VFP isn't
present.  Unfortunately, the kernel hard-codes VFP instructions
into the thread switch, which prevents this being run-time selectable.

Solve this by introducing a notifier which things such as VFP can
hook into to be informed of events which affect the VFP subsystem
(eg, creation and destruction of threads, switches between threads.)

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

1 files changed, 46 insertions, 25 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 03486be04193..2476f4c2e760 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -15,6 +15,8 @@
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/init.h>
+
+#include <asm/thread_notify.h>
 #include <asm/vfp.h>
 
 #include "vfpinstr.h"
@@ -36,38 +38,55 @@ union vfp_state *last_VFP_context;
  */
 unsigned int VFP_arch;
 
-/*
- * Per-thread VFP initialisation.
- */
-void vfp_flush_thread(union vfp_state *vfp)
+static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
 {
-        memset(vfp, 0, sizeof(union vfp_state));
+        struct thread_info *thread = v;
+        union vfp_state *vfp = &thread->vfpstate;
 
-        vfp->hard.fpexc = FPEXC_ENABLE;
-        vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
+        switch (cmd) {
+        case THREAD_NOTIFY_FLUSH:
+                /*
+                 * Per-thread VFP initialisation.
+                 */
+                memset(vfp, 0, sizeof(union vfp_state));
 
-        /*
-         * Disable VFP to ensure we initialise it first.
-         */
-        fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+                vfp->hard.fpexc = FPEXC_ENABLE;
+                vfp->hard.fpscr = FPSCR_ROUND_NEAREST;
 
-        /*
-         * Ensure we don't try to overwrite our newly initialised
-         * state information on the first fault.
-         */
-        if (last_VFP_context == vfp)
-                last_VFP_context = NULL;
-}
+                /*
+                 * Disable VFP to ensure we initialise it first.
+                 */
+                fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
 
-/*
- * Per-thread VFP cleanup.
- */
-void vfp_release_thread(union vfp_state *vfp)
-{
-        if (last_VFP_context == vfp)
-                last_VFP_context = NULL;
+                /*
+                 * FALLTHROUGH: Ensure we don't try to overwrite our newly
+                 * initialised state information on the first fault.
+                 */
+
+        case THREAD_NOTIFY_RELEASE:
+                /*
+                 * Per-thread VFP cleanup.
+                 */
+                if (last_VFP_context == vfp)
+                        last_VFP_context = NULL;
+                break;
+
+        case THREAD_NOTIFY_SWITCH:
+                /*
+                 * Always disable VFP so we can lazily save/restore the
+                 * old state.
+                 */
+                fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_ENABLE);
+                break;
+        }
+
+        return NOTIFY_DONE;
 }
 
+static struct notifier_block vfp_notifier_block = {
+        .notifier_call  = vfp_notifier,
+};
+
 /*
  * Raise a SIGFPE for the current process.
  * sicode describes the signal being raised.
@@ -281,6 +300,8 @@ static int __init vfp_init(void)
                         (vfpsid & FPSID_VARIANT_MASK) >> FPSID_VARIANT_BIT,
                         (vfpsid & FPSID_REV_MASK) >> FPSID_REV_BIT);
                 vfp_vector = vfp_support_entry;
+
+                thread_register_notifier(&vfp_notifier_block);
         }
         return 0;
 }