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>

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 68b7562..44a5d0a 100644 (file)
--- 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]);