drm/mxsfb: Fix initial corrupt frame when activating display

LCDIF will repeatedly display data from CUR_BUF and set CUR_BUF to
NEXT_BUF when done. Since we are only ever writing to NEXT_BUF the
display will show an initial corrupt frame.

Fix by writing the FB paddr to both CUR_BUF and NEXT_BUF when
activating the CRTC.
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/7cdac9c064cc2b8a3d237934f186da98cefe6cb3.1537191359.git.leonard.crestez@nxp.com

drivers/gpu/drm/mxsfb/mxsfb_crtc.c

@@ -193,6 +193,21 @@ static int mxsfb_reset_block(void __iomem *reset_addr)
 	return clear_poll_bit(reset_addr, MODULE_CLKGATE);
 }
 
+static dma_addr_t mxsfb_get_fb_paddr(struct mxsfb_drm_private *mxsfb)
+{
+	struct drm_framebuffer *fb = mxsfb->pipe.plane.state->fb;
+	struct drm_gem_cma_object *gem;
+
+	if (!fb)
+		return 0;
+
+	gem = drm_fb_cma_get_gem_obj(fb, 0);
+	if (!gem)
+		return 0;
+
+	return gem->paddr;
+}
+
 static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 {
 	struct drm_display_mode *m = &mxsfb->pipe.crtc.state->adjusted_mode;
@@ -269,8 +284,18 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 
 void mxsfb_crtc_enable(struct mxsfb_drm_private *mxsfb)
 {
+	dma_addr_t paddr;
+
 	mxsfb_enable_axi_clk(mxsfb);
 	mxsfb_crtc_mode_set_nofb(mxsfb);
+
+	/* Write cur_buf as well to avoid an initial corrupt frame */
+	paddr = mxsfb_get_fb_paddr(mxsfb);
+	if (paddr) {
+		writel(paddr, mxsfb->base + mxsfb->devdata->cur_buf);
+		writel(paddr, mxsfb->base + mxsfb->devdata->next_buf);
+	}
+
 	mxsfb_enable_controller(mxsfb);
 }
 
@@ -285,12 +310,8 @@ void mxsfb_plane_atomic_update(struct mxsfb_drm_private *mxsfb,
 {
 	struct drm_simple_display_pipe *pipe = &mxsfb->pipe;
 	struct drm_crtc *crtc = &pipe->crtc;
-	struct drm_framebuffer *fb = pipe->plane.state->fb;
 	struct drm_pending_vblank_event *event;
-	struct drm_gem_cma_object *gem;
-
-	if (!crtc)
-		return;
+	dma_addr_t paddr;
 
 	spin_lock_irq(&crtc->dev->event_lock);
 	event = crtc->state->event;
@@ -305,12 +326,10 @@ void mxsfb_plane_atomic_update(struct mxsfb_drm_private *mxsfb,
 	}
 	spin_unlock_irq(&crtc->dev->event_lock);
 
-	if (!fb)
-		return;
-
-	gem = drm_fb_cma_get_gem_obj(fb, 0);
-
+	paddr = mxsfb_get_fb_paddr(mxsfb);
+	if (paddr) {
 		mxsfb_enable_axi_clk(mxsfb);
-	writel(gem->paddr, mxsfb->base + mxsfb->devdata->next_buf);
+		writel(paddr, mxsfb->base + mxsfb->devdata->next_buf);
 		mxsfb_disable_axi_clk(mxsfb);
+	}
 }