drm/vc4: Account for interrupts in flight

Synchronously disable the IRQ to make the following cancel_work_sync
invocation effective.

An interrupt in flight could enqueue further overflow mem work. As we
free the binner BO immediately following vc4_irq_uninstall this caused
a NULL pointer dereference in the work callback vc4_overflow_mem_work.

Link: anholt/linux#114
Signed-off-by: Stefan Schake <stschake@gmail.com>
Fixes: d5b1a78 ("drm/vc4: Add support for drawing 3D frames.")
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1510275907-993-2-git-send-email-stschake@gmail.com
(cherry picked from commit 253696ccd613fbdaa5aba1de44c461a058e0a114)

drivers/gpu/drm/vc4/vc4_irq.c

@@ -204,6 +204,9 @@ vc4_irq_postinstall(struct drm_device *dev)
 {
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 
+	/* Undo the effects of a previous vc4_irq_uninstall. */
+	enable_irq(dev->irq);
+
 	/* Enable both the render done and out of memory interrupts. */
 	V3D_WRITE(V3D_INTENA, V3D_DRIVER_IRQS);