drm: mxsfb: Enable vblank handling

Enable vblank handling when the CRTC is turned on and disable it when it
is turned off. This requires moving vblank init after the KMS pipeline
initialisation, otherwise drm_vblank_init() gets called with 0 CRTCs.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200727020654.8231-15-laurent.pinchart@ideasonboard.com

drivers/gpu/drm/mxsfb/mxsfb_drv.c

@@ -161,12 +161,6 @@ static int mxsfb_load(struct drm_device *drm)
 
 	pm_runtime_enable(drm->dev);
 
-	ret = drm_vblank_init(drm, drm->mode_config.num_crtc);
-	if (ret < 0) {
-		dev_err(drm->dev, "Failed to initialise vblank\n");
-		goto err_vblank;
-	}
-
 	/* Modeset init */
 	drm_mode_config_init(drm);
 
@@ -176,6 +170,15 @@ static int mxsfb_load(struct drm_device *drm)
 		goto err_vblank;
 	}
 
+	ret = drm_vblank_init(drm, drm->mode_config.num_crtc);
+	if (ret < 0) {
+		dev_err(drm->dev, "Failed to initialise vblank\n");
+		goto err_vblank;
+	}
+
+	/* Start with vertical blanking interrupt reporting disabled. */
+	drm_crtc_vblank_off(&mxsfb->crtc);
+
 	ret = mxsfb_attach_bridge(mxsfb);
 	if (ret) {
 		dev_err(drm->dev, "Cannot connect bridge: %d\n", ret);

drivers/gpu/drm/mxsfb/mxsfb_kms.c

@@ -322,8 +322,10 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
 	dma_addr_t paddr;
 
 	pm_runtime_get_sync(drm->dev);
-
 	mxsfb_enable_axi_clk(mxsfb);
+
+	drm_crtc_vblank_on(crtc);
+
 	mxsfb_crtc_mode_set_nofb(mxsfb);
 
 	/* Write cur_buf as well to avoid an initial corrupt frame */
@@ -353,6 +355,8 @@ static void mxsfb_crtc_atomic_disable(struct drm_crtc *crtc,
 	}
 	spin_unlock_irq(&drm->event_lock);
 
+	drm_crtc_vblank_off(crtc);
+
 	mxsfb_disable_axi_clk(mxsfb);
 	pm_runtime_put_sync(drm->dev);
 }