drm/armada: redo locking and atomics for armada_drm_crtc_complete_frame_work()

We can do better with armada_drm_crtc_complete_frame_work() - we can
avoid taking the event lock unless a call to drm_send_vblank_event()
is required, and using cmpxchg() and xchg(), we can eliminate the
locking around dcrtc->frame_work entirely.

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

diff --git a/drivers/gpu/drm/armada/armada_crtc.c b/drivers/gpu/drm/armada/armada_crtc.c
index 8c43ecc..5d62764 100644 (file)
--- a/drivers/gpu/drm/armada/armada_crtc.c
+++ b/drivers/gpu/drm/armada/armada_crtc.c
@@ -215,7 +215,6 @@ static int armada_drm_crtc_queue_frame_work(struct armada_crtc *dcrtc,
        struct armada_frame_work *work)
 {
        struct drm_device *dev = dcrtc->crtc.dev;
-       unsigned long flags;
        int ret;
 
        ret = drm_vblank_get(dev, dcrtc->num);
@@ -224,30 +223,29 @@ static int armada_drm_crtc_queue_frame_work(struct armada_crtc *dcrtc,
                return ret;
        }
 
-       spin_lock_irqsave(&dev->event_lock, flags);
-       if (!dcrtc->frame_work)
-               dcrtc->frame_work = work;
-       else
-               ret = -EBUSY;
-       spin_unlock_irqrestore(&dev->event_lock, flags);
-
-       if (ret)
+       if (cmpxchg(&dcrtc->frame_work, NULL, work)) {
                drm_vblank_put(dev, dcrtc->num);
+               ret = -EBUSY;
+       }
 
        return ret;
 }
 
-static void armada_drm_crtc_complete_frame_work(struct armada_crtc *dcrtc)
+static void armada_drm_crtc_complete_frame_work(struct armada_crtc *dcrtc,
+       struct armada_frame_work *work)
 {
        struct drm_device *dev = dcrtc->crtc.dev;
-       struct armada_frame_work *work = dcrtc->frame_work;
-
-       dcrtc->frame_work = NULL;
+       unsigned long flags;
 
+       spin_lock_irqsave(&dcrtc->irq_lock, flags);
        armada_drm_crtc_update_regs(dcrtc, work->regs);
+       spin_unlock_irqrestore(&dcrtc->irq_lock, flags);
 
-       if (work->event)
+       if (work->event) {
+               spin_lock_irqsave(&dev->event_lock, flags);
                drm_send_vblank_event(dev, dcrtc->num, work->event);
+               spin_unlock_irqrestore(&dev->event_lock, flags);
+       }
 
        drm_vblank_put(dev, dcrtc->num);
 
@@ -293,7 +291,7 @@ static void armada_drm_crtc_finish_fb(struct armada_crtc *dcrtc,
 
 static void armada_drm_vblank_off(struct armada_crtc *dcrtc)
 {
-       struct drm_device *dev = dcrtc->crtc.dev;
+       struct armada_frame_work *work;
 
        /*
         * Tell the DRM core that vblank IRQs aren't going to happen for
@@ -302,10 +300,9 @@ static void armada_drm_vblank_off(struct armada_crtc *dcrtc)
        drm_crtc_vblank_off(&dcrtc->crtc);
 
        /* Handle any pending flip event. */
-       spin_lock_irq(&dev->event_lock);
-       if (dcrtc->frame_work)
-               armada_drm_crtc_complete_frame_work(dcrtc);
-       spin_unlock_irq(&dev->event_lock);
+       work = xchg(&dcrtc->frame_work, NULL);
+       if (work)
+               armada_drm_crtc_complete_frame_work(dcrtc, work);
 }
 
 void armada_drm_crtc_gamma_set(struct drm_crtc *crtc, u16 r, u16 g, u16 b,
@@ -434,12 +431,10 @@ static void armada_drm_crtc_irq(struct armada_crtc *dcrtc, u32 stat)
        spin_unlock(&dcrtc->irq_lock);
 
        if (stat & GRA_FRAME_IRQ) {
-               struct drm_device *dev = dcrtc->crtc.dev;
+               struct armada_frame_work *work = xchg(&dcrtc->frame_work, NULL);
 
-               spin_lock(&dev->event_lock);
-               if (dcrtc->frame_work)
-                       armada_drm_crtc_complete_frame_work(dcrtc);
-               spin_unlock(&dev->event_lock);
+               if (work)
+                       armada_drm_crtc_complete_frame_work(dcrtc, work);
 
                wake_up(&dcrtc->frame_wait);
        }
@@ -957,8 +952,6 @@ static int armada_drm_crtc_page_flip(struct drm_crtc *crtc,
 {
        struct armada_crtc *dcrtc = drm_to_armada_crtc(crtc);
        struct armada_frame_work *work;
-       struct drm_device *dev = crtc->dev;
-       unsigned long flags;
        unsigned i;
        int ret;
 
@@ -1004,10 +997,10 @@ static int armada_drm_crtc_page_flip(struct drm_crtc *crtc,
         * interrupt, so complete it now.
         */
        if (dpms_blanked(dcrtc->dpms)) {
-               spin_lock_irqsave(&dev->event_lock, flags);
-               if (dcrtc->frame_work)
-                       armada_drm_crtc_complete_frame_work(dcrtc);
-               spin_unlock_irqrestore(&dev->event_lock, flags);
+               struct armada_frame_work *work = xchg(&dcrtc->frame_work, NULL);
+
+               if (work)
+                       armada_drm_crtc_complete_frame_work(dcrtc, work);
        }
 
        return 0;