[PATCH 08/20] drm/armada: use xchg() to atomically update dplane->old_fb

[Russell King]

Rather than using a spinlock, use xchg() to atomically update
dplane->old_fb.  This allows us to eliminate dplane->lock.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/gpu/drm/armada/armada_overlay.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/armada/armada_overlay.c 
b/drivers/gpu/drm/armada/armada_overlay.c
index 093c2d4f2b79..8738b590abc2 100644
--- a/drivers/gpu/drm/armada/armada_overlay.c
+++ b/drivers/gpu/drm/armada/armada_overlay.c
@@ -31,7 +31,6 @@ struct armada_ovl_plane_properties {

 struct armada_ovl_plane {
        struct drm_plane base;
-       spinlock_t lock;
        struct drm_framebuffer *old_fb;
        uint32_t src_hw;
        uint32_t dst_hw;
@@ -76,13 +75,10 @@ static void armada_ovl_retire_fb(struct armada_ovl_plane 
*dplane,
 {
        struct drm_framebuffer *old_fb;

-       spin_lock(&dplane->lock);
-       old_fb = dplane->old_fb;
-       dplane->old_fb = fb;
-       spin_unlock(&dplane->lock);
+       old_fb = xchg(&dplane->old_fb, fb);

        if (old_fb)
-               armada_drm_queue_unref_work(dplane->base.dev, old_fb);
+               armada_drm_queue_unref_work(dplane->base.base.dev, old_fb);
 }

 /* === Plane support === */
@@ -289,10 +285,7 @@ static int armada_ovl_plane_disable(struct drm_plane 
*plane)
        if (plane->fb)
                drm_framebuffer_unreference(plane->fb);

-       spin_lock_irq(&dplane->lock);
-       fb = dplane->old_fb;
-       dplane->old_fb = NULL;
-       spin_unlock_irq(&dplane->lock);
+       fb = xchg(&dplane->old_fb, NULL);
        if (fb)
                drm_framebuffer_unreference(fb);

@@ -464,7 +457,6 @@ int armada_overlay_plane_create(struct drm_device *dev, 
unsigned long crtcs)
        if (!dplane)
                return -ENOMEM;

-       spin_lock_init(&dplane->lock);
        init_waitqueue_head(&dplane->vbl.wait);
        armada_drm_vbl_event_init(&dplane->vbl.update, armada_ovl_plane_vbl,
                                  dplane);
-- 
2.1.0