drm/omap: fix incorrect lock state

After commit 92cc68e ("drm/vblank: Use
spin_(un)lock_irq() in drm_crtc_vblank_on()") omapdrm locking is broken:

WARNING: inconsistent lock state
5.8.0-rc2-00483-g92cc68e35863 #13 Tainted: G        W
--------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
ea98222c (&dev->event_lock#2){?.+.}-{2:2}, at: drm_handle_vblank+0x4c/0x520 [drm]
{HARDIRQ-ON-W} state was registered at:
  trace_hardirqs_on+0x9c/0x1ec
  _raw_spin_unlock_irq+0x20/0x58
  omap_crtc_atomic_enable+0x54/0xa0 [omapdrm]
  drm_atomic_helper_commit_modeset_enables+0x218/0x270 [drm_kms_helper]
  omap_atomic_commit_tail+0x48/0xc4 [omapdrm]
  commit_tail+0x9c/0x190 [drm_kms_helper]
  drm_atomic_helper_commit+0x154/0x188 [drm_kms_helper]
  drm_client_modeset_commit_atomic+0x228/0x268 [drm]
  drm_client_modeset_commit_locked+0x60/0x1d0 [drm]
  drm_client_modeset_commit+0x24/0x40 [drm]
  drm_fb_helper_restore_fbdev_mode_unlocked+0x54/0xa8 [drm_kms_helper]
  drm_fb_helper_set_par+0x2c/0x5c [drm_kms_helper]
  drm_fb_helper_hotplug_event.part.0+0xa0/0xbc [drm_kms_helper]
  drm_kms_helper_hotplug_event+0x24/0x30 [drm_kms_helper]
  output_poll_execute+0x1a8/0x1c0 [drm_kms_helper]
  process_one_work+0x268/0x800
  worker_thread+0x30/0x4e0
  kthread+0x164/0x190
  ret_from_fork+0x14/0x20

The reason for this is that omapdrm calls drm_crtc_vblank_on() while
holding event_lock taken with spin_lock_irq().

It is not clear why drm_crtc_vblank_on() and drm_crtc_vblank_get() are
called while holding event_lock. I don't see any problem with moving
those calls outside the lock, which is what this patch does.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200819103021.440288-1-tomi.valkeinen@ti.com
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/omapdrm/omap_crtc.c

@@ -451,11 +451,12 @@ static void omap_crtc_atomic_enable(struct drm_crtc *crtc,
 	if (omap_state->manually_updated)
 		return;
 
-	spin_lock_irq(&crtc->dev->event_lock);
 	drm_crtc_vblank_on(crtc);
+
 	ret = drm_crtc_vblank_get(crtc);
 	WARN_ON(ret != 0);
 
+	spin_lock_irq(&crtc->dev->event_lock);
 	omap_crtc_arm_event(crtc);
 	spin_unlock_irq(&crtc->dev->event_lock);
 }