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

[Russell King - ARM Linux]

On Wed, Sep 30, 2015 at 11:49:44AM +0100, Emil Velikov wrote:
> Hi Russell,
> 
> On 29 September 2015 at 19:10, Russell King  
> wrote:
> > 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 
> > ---
> [...]
> > @@ -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);
> Shouldn't this be part of another patch ?

Yes, you're right, it should be in:

drm/armada: introduce generic armada_plane struct

Now moved there, thanks.

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

[Emil Velikov]

Hi Russell,

On 29 September 2015 at 19:10, Russell King  
wrote:
> 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 
> ---
[...]
> @@ -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);
Shouldn't this be part of another patch ?

-Emil

[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 
---
 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