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Commit d53dab3a authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Dave Airlie
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarMario Kleiner <mario.kleiner@tuebingen.mpg.de>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent a7c36fd8

drivers/gpu/drm/drm_irq.c

+0 −9
Original line number Diff line number Diff line
@@ -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]);