drm: atmel_hlcdc: Enable the crtc vblank prior to crtc usage.

'commit eec44d44 ("drm/atmel: Use drm_atomic_helper_commit")'
removed the home-grown handling of atomic commits and exposed an issue
in the crtc atomic commit handling where vblank is expected to be
enabled but hasn't yet, causing kernel warnings during boot.  This patch
cleans up the crtc vblank handling thus removing the warning on boot.

Fixes: eec44d44 ("drm/atmel: Use drm_atomic_helper_commit")
Signed-off-by: Dan Sneddon <dan.sneddon@microchip.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602160846.5013-1-dan.sneddon@microchip.com

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c

@@ -232,7 +232,6 @@ static void atmel_hlcdc_crtc_atomic_enable(struct drm_crtc *c,
 
 	pm_runtime_put_sync(dev->dev);
 
-	drm_crtc_vblank_on(c);
 }
 
 #define ATMEL_HLCDC_RGB444_OUTPUT	BIT(0)
@@ -343,8 +342,17 @@ static int atmel_hlcdc_crtc_atomic_check(struct drm_crtc *c,
 
 static void atmel_hlcdc_crtc_atomic_begin(struct drm_crtc *c,
 					  struct drm_atomic_state *state)
+{
+	drm_crtc_vblank_on(c);
+}
+
+static void atmel_hlcdc_crtc_atomic_flush(struct drm_crtc *c,
+					  struct drm_atomic_state *state)
 {
 	struct atmel_hlcdc_crtc *crtc = drm_crtc_to_atmel_hlcdc_crtc(c);
+	unsigned long flags;
+
+	spin_lock_irqsave(&c->dev->event_lock, flags);
 
 	if (c->state->event) {
 		c->state->event->pipe = drm_crtc_index(c);
@@ -354,12 +362,7 @@ static void atmel_hlcdc_crtc_atomic_begin(struct drm_crtc *c,
 		crtc->event = c->state->event;
 		c->state->event = NULL;
 	}
-}
-
-static void atmel_hlcdc_crtc_atomic_flush(struct drm_crtc *crtc,
-					  struct drm_atomic_state *state)
-{
-	/* TODO: write common plane control register if available */
+	spin_unlock_irqrestore(&c->dev->event_lock, flags);
 }
 
 static const struct drm_crtc_helper_funcs lcdc_crtc_helper_funcs = {