drm: Remove utterly bogus preempt_disable() sections

commit 27641c3f (drm/vblank: Add support for precise vblank
timestamping) adds preempt_disable()/enable() around a spin locked
section with the comments:

 * Disable preemption, so vblank_time_lock is held as short as
 * possible, even under a kernel with PREEMPT_RT patches.

/* Disable preemption while holding vblank_time_lock. Do
 * it explicitely to guard against PREEMPT_RT kernel.

Just that this has never been tested on a RT kernel which would have
granted that nonsense with a might_sleep() warning because
dev->vblank_time_lock is converted to a "sleeping" spinlock on RT.

So this is activly wrong on RT and superflous on mainline. Remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 0 insertions, 9 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 68b756253f9f..44a5d0ad8b7c 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -110,10 +110,7 @@ static void vblank_disable_and_save(struct drm_device *dev, int crtc)
         /* Prevent vblank irq processing while disabling vblank irqs,
          * so no updates of timestamps or count can happen after we've
          * disabled. Needed to prevent races in case of delayed irq's.
-         * Disable preemption, so vblank_time_lock is held as short as
-         * possible, even under a kernel with PREEMPT_RT patches.
          */
-        preempt_disable();
         spin_lock_irqsave(&dev->vblank_time_lock, irqflags);
 
         dev->driver->disable_vblank(dev, crtc);
@@ -164,7 +161,6 @@ static void vblank_disable_and_save(struct drm_device *dev, int crtc)
         clear_vblank_timestamps(dev, crtc);
 
         spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
-        preempt_enable();
 }
 
 static void vblank_disable_fn(unsigned long arg)
@@ -889,10 +885,6 @@ int drm_vblank_get(struct drm_device *dev, int crtc)
         spin_lock_irqsave(&dev->vbl_lock, irqflags);
         /* Going from 0->1 means we have to enable interrupts again */
         if (atomic_add_return(1, &dev->vblank_refcount[crtc]) == 1) {
-                /* Disable preemption while holding vblank_time_lock. Do
-                 * it explicitely to guard against PREEMPT_RT kernel.
-                 */
-                preempt_disable();
                 spin_lock_irqsave(&dev->vblank_time_lock, irqflags2);
                 if (!dev->vblank_enabled[crtc]) {
                         /* Enable vblank irqs under vblank_time_lock protection.
@@ -912,7 +904,6 @@ int drm_vblank_get(struct drm_device *dev, int crtc)
                         }
                 }
                 spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags2);
-                preempt_enable();
         } else {
                 if (!dev->vblank_enabled[crtc]) {
                         atomic_dec(&dev->vblank_refcount[crtc]);