drm: renesas: shmobile: Turn vblank on/off when enabling/disabling CRTC

The DRM core vblank handling mechanism requires drivers to forcefully
turn vblank reporting off when disabling the CRTC, and to restore the
vblank reporting status when enabling the CRTC.
Implement this using the drm_crtc_vblank_{on,off}() helpers.

Note that drm_crtc_vblank_off() must be called at startup to synchronize
the state of the vblank core code with the hardware, which is initially
disabled.  This is performed at CRTC creation time, requiring vertical
blank initialization to be moved before creating CRTCs.
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/e5833e5706b7792bfca8e6e56fc154a7c3e0574f.1694767209.git.geert+renesas@glider.be

drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c

@@ -271,6 +271,9 @@ static void shmob_drm_crtc_start(struct shmob_drm_crtc *scrtc)
 
 	shmob_drm_crtc_start_stop(scrtc, true);
 
+	/* Turn vertical blank interrupt reporting back on. */
+	drm_crtc_vblank_on(crtc);
+
 	scrtc->started = true;
 }
 
@@ -283,10 +286,12 @@ static void shmob_drm_crtc_stop(struct shmob_drm_crtc *scrtc)
 		return;
 
 	/*
-	 * Wait for page flip completion before stopping the CRTC as userspace
+	 * Disable vertical blank interrupt reporting.  We first need to wait
+	 * for page flip completion before stopping the CRTC as userspace
 	 * expects page flips to eventually complete.
 	 */
 	shmob_drm_crtc_wait_page_flip(scrtc);
+	drm_crtc_vblank_off(crtc);
 
 	/* Stop the LCDC. */
 	shmob_drm_crtc_start_stop(scrtc, false);
@@ -519,6 +524,9 @@ int shmob_drm_crtc_create(struct shmob_drm_device *sdev)
 
 	drm_crtc_helper_add(crtc, &crtc_helper_funcs);
 
+	/* Start with vertical blank interrupt reporting disabled. */
+	drm_crtc_vblank_off(crtc);
+
 	return 0;
 }
 

drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c

@@ -215,17 +215,17 @@ static int shmob_drm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	ret = shmob_drm_modeset_init(sdev);
-	if (ret < 0)
-		return dev_err_probe(&pdev->dev, ret,
-				     "failed to initialize mode setting\n");
-
 	ret = drm_vblank_init(ddev, 1);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to initialize vblank\n");
-		goto err_modeset_cleanup;
+		return ret;
 	}
 
+	ret = shmob_drm_modeset_init(sdev);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret,
+				     "failed to initialize mode setting\n");
+
 	ret = platform_get_irq(pdev, 0);
 	if (ret < 0)
 		goto err_modeset_cleanup;