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

From: Russell King <rmk+kernel@arm.linux.org.uk>
To: dri-devel@lists.freedesktop.org
Subject: [PATCH 08/20] drm/armada: use xchg() to atomically update dplane->old_fb
Date: Tue, 29 Sep 2015 19:10:09 +0100	[thread overview]
Message-ID: <E1ZgzLt-0003lG-Aq@rmk-PC.arm.linux.org.uk> (raw)
In-Reply-To: <20150929180843.GP21513@n2100.arm.linux.org.uk>

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@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

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