3 files changed, 43 insertions, 13 deletions

diff --git a/drivers/gpu/drm/pl111/Kconfig b/drivers/gpu/drm/pl111/Kconfig
index e5e2abd66491..82cb3e60ddc8 100644
--- a/drivers/gpu/drm/pl111/Kconfig
+++ b/drivers/gpu/drm/pl111/Kconfig
@@ -8,6 +8,7 @@ config DRM_PL111
 	select DRM_GEM_CMA_HELPER
 	select DRM_BRIDGE
 	select DRM_PANEL_BRIDGE
+	select DRM_DUMB_VGA_DAC
 	select VT_HW_CONSOLE_BINDING if FRAMEBUFFER_CONSOLE
 	help
 	  Choose this option for DRM support for the PL111 CLCD controller.
diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
index 06c4bf756b69..7fe4040aea46 100644
--- a/drivers/gpu/drm/pl111/pl111_display.c
+++ b/drivers/gpu/drm/pl111/pl111_display.c
@@ -94,6 +94,7 @@ static void pl111_display_enable(struct drm_simple_display_pipe *pipe,
 	const struct drm_display_mode *mode = &cstate->mode;
 	struct drm_framebuffer *fb = plane->state->fb;
 	struct drm_connector *connector = priv->connector;
+	struct drm_bridge *bridge = priv->bridge;
 	u32 cntl;
 	u32 ppl, hsw, hfp, hbp;
 	u32 lpp, vsw, vfp, vbp;
@@ -143,11 +144,37 @@ static void pl111_display_enable(struct drm_simple_display_pipe *pipe,
 	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
 		tim2 |= TIM2_IVS;
 
-	if (connector->display_info.bus_flags & DRM_BUS_FLAG_DE_LOW)
-		tim2 |= TIM2_IOE;
+	if (connector) {
+		if (connector->display_info.bus_flags & DRM_BUS_FLAG_DE_LOW)
+			tim2 |= TIM2_IOE;
 
-	if (connector->display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
-		tim2 |= TIM2_IPC;
+		if (connector->display_info.bus_flags &
+		    DRM_BUS_FLAG_PIXDATA_NEGEDGE)
+			tim2 |= TIM2_IPC;
+	}
+
+	if (bridge) {
+		const struct drm_bridge_timings *btimings = bridge->timings;
+
+		/*
+		 * Here is when things get really fun. Sometimes the bridge
+		 * timings are such that the signal out from PL11x is not
+		 * stable before the receiving bridge (such as a dumb VGA DAC
+		 * or similar) samples it. If that happens, we compensate by
+		 * the only method we have: output the data on the opposite
+		 * edge of the clock so it is for sure stable when it gets
+		 * sampled.
+		 *
+		 * The PL111 manual does not contain proper timining diagrams
+		 * or data for these details, but we know from experiments
+		 * that the setup time is more than 3000 picoseconds (3 ns).
+		 * If we have a bridge that requires the signal to be stable
+		 * earlier than 3000 ps before the clock pulse, we have to
+		 * output the data on the opposite edge to avoid flicker.
+		 */
+		if (btimings && btimings->setup_time_ps >= 3000)
+			tim2 ^= TIM2_IPC;
+	}
 
 	tim2 |= cpl << 16;
 	writel(tim2, priv->regs + CLCD_TIM2);
diff --git a/drivers/gpu/drm/pl111/pl111_drv.c b/drivers/gpu/drm/pl111/pl111_drv.c
index acb738c69873..19e1725c3ef6 100644
--- a/drivers/gpu/drm/pl111/pl111_drv.c
+++ b/drivers/gpu/drm/pl111/pl111_drv.c
@@ -108,11 +108,17 @@ static int pl111_modeset_init(struct drm_device *dev)
 			ret = PTR_ERR(bridge);
 			goto out_config;
 		}
-		/*
-		 * TODO: when we are using a different bridge than a panel
-		 * (such as a dumb VGA connector) we need to devise a different
-		 * method to get the connector out of the bridge.
-		 */
+	} else if (bridge) {
+		dev_info(dev->dev, "Using non-panel bridge\n");
+	} else {
+		dev_err(dev->dev, "No bridge, exiting\n");
+		return -ENODEV;
+	}
+
+	priv->bridge = bridge;
+	if (panel) {
+		priv->panel = panel;
+		priv->connector = panel->connector;
 	}
 
 	ret = pl111_display_init(dev);
@@ -126,10 +132,6 @@ static int pl111_modeset_init(struct drm_device *dev)
 	if (ret)
 		return ret;
 
-	priv->bridge = bridge;
-	priv->panel = panel;
-	priv->connector = panel->connector;
-
 	ret = drm_vblank_init(dev, 1);
 	if (ret != 0) {
 		dev_err(dev->dev, "Failed to init vblank\n");