WIP, hack in VGA666 as a dumb-vga-dac bridge

arch/arm/boot/dts/bcm2835-rpi.dtsi

@@ -9,6 +9,9 @@
 	leds {
 		compatible = "gpio-leds";
 
+		pinctrl-names = "default";
+		pinctrl-0 = <&vga666_pins>;
+
 		act {
 			label = "ACT";
 			default-state = "keep";
@@ -42,6 +45,13 @@
 		brcm,pins = <4 5 7 8 9 10 11 14 15>;
 		brcm,function = <BCM2835_FSEL_ALT0>;
 	};
+
+	vga666_pins: vga666_pins {
+		brcm,pins = <2 3 4 5 6 7 8 9 10 11 12
+ 		             13 14 15 16 17 18 19 20 21>;
+		brcm,function = <6>; /* alt2 */
+		brcm,pull = <0>; /* no pull */
+	};
 };
 
 &i2c0 {

arch/arm/boot/dts/bcm283x.dtsi

@@ -422,6 +422,24 @@
 
 		};
 
+		/* begin added DPI */
+		dpi: dpi@7e208000 {
+			compatible = "brcm,bcm2835-dpi";
+			reg = <0x7e208000 0x8c>;
+			clocks = <&clocks BCM2835_CLOCK_VPU>,
+				 <&clocks BCM2835_CLOCK_DPI>;
+			clock-names = "core", "pixel";
+			#address-cells = <1>;
+			#size-cells = <0>;
+			status = "okay";
+			port {
+				dpi_out: endpoint@0 {
+					remote-endpoint = <&vga_bridge_in>;
+				};
+			};
+		};
+		/* end added DPI */
+
 		thermal: thermal@7e212000 {
 			compatible = "brcm,bcm2835-thermal";
 			reg = <0x7e212000 0x8>;
@@ -627,4 +645,41 @@
 			clock-frequency = <480000000>;
 		};
 	};
+
+	bridge {
+		compatible = "dumb-vga-dac";
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		ports {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			port@0 {
+				reg = <0>;
+
+				vga_bridge_in: endpoint {
+					remote-endpoint = <&dpi_out>;
+				};
+			};
+
+			port@1 {
+				reg = <1>;
+
+				vga_bridge_out: endpoint {
+					remote-endpoint = <&vga_con_in>;
+				};
+			};
+		};
+	};
+
+	vga {
+		compatible = "vga-connector";
+
+		port {
+			vga_con_in: endpoint {
+				remote-endpoint = <&vga_bridge_out>;
+			};
+		};
+	};
 };

drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c

@@ -399,6 +399,9 @@ static struct i2c_client *rpi_touchscreen_get_i2c(struct device *dev,
 
 	of_node_put(node);
 
+	if (!client)
+		return ERR_PTR(-EPROBE_DEFER);
+
 	return client;
 }
 

drivers/gpu/drm/vc4/vc4_dpi.c

@@ -161,7 +161,11 @@ static void vc4_dpi_encoder_disable(struct drm_encoder *encoder)
 	struct vc4_dpi_encoder *vc4_encoder = to_vc4_dpi_encoder(encoder);
 	struct vc4_dpi *dpi = vc4_encoder->dpi;
 
+	drm_bridge_disable(dpi->bridge);
+
 	clk_disable_unprepare(dpi->pixel_clock);
+
+	drm_bridge_post_disable(dpi->bridge);
 }
 
 static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
@@ -172,7 +176,9 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 	u32 dpi_c = DPI_ENABLE | DPI_OUTPUT_ENABLE_MODE;
 	int ret;
 
-	if (dpi->connector->display_info.num_bus_formats) {
+	drm_bridge_pre_enable(dpi->bridge);
+
+	if (dpi->connector && dpi->connector->display_info.num_bus_formats) {
 		u32 bus_format = dpi->connector->display_info.bus_formats[0];
 
 		switch (bus_format) {
@@ -201,8 +207,13 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 			DRM_ERROR("Unknown media bus format %d\n", bus_format);
 			break;
 		}
+	} else {
+		DRM_ERROR("mode=%p vc4_encoder=%p dpi=%p dpi->connector=%p\n",
+		          mode, vc4_encoder, dpi, dpi->connector);
+		dpi_c |= VC4_SET_FIELD(DPI_FORMAT_18BIT_666_RGB_1, DPI_FORMAT);
 	}
 
+	/*
 	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
 		dpi_c |= DPI_HSYNC_INVERT;
 	else if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
@@ -212,6 +223,7 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 		dpi_c |= DPI_VSYNC_INVERT;
 	else if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
 		dpi_c |= DPI_VSYNC_DISABLE;
+	*/
 
 	DPI_WRITE(DPI_C, dpi_c);
 
@@ -222,6 +234,8 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
 	ret = clk_prepare_enable(dpi->pixel_clock);
 	if (ret)
 		DRM_ERROR("Failed to set clock rate: %d\n", ret);
+
+	drm_bridge_enable(dpi->bridge);
 }
 
 static bool vc4_dpi_encoder_mode_fixup(struct drm_encoder *encoder,
@@ -298,8 +312,10 @@ static int vc4_dpi_bind(struct device *dev, struct device *master, void *data)
 
 	dpi->pdev = pdev;
 	dpi->regs = vc4_ioremap_regs(pdev, 0);
-	if (IS_ERR(dpi->regs))
+	if (IS_ERR(dpi->regs)) {
+		dev_err(dev, "DPI reg error: %ld\n", PTR_ERR(dpi->regs));
 		return PTR_ERR(dpi->regs);
+	}
 
 	if (DPI_READ(DPI_ID) != DPI_ID_VALUE) {
 		dev_err(dev, "Port returned 0x%08x for ID instead of 0x%08x\n",
@@ -310,13 +326,15 @@ static int vc4_dpi_bind(struct device *dev, struct device *master, void *data)
 	dpi->core_clock = devm_clk_get(dev, "core");
 	if (IS_ERR(dpi->core_clock)) {
 		ret = PTR_ERR(dpi->core_clock);
+		dev_err(dev, "DPI core clock error: %d\n", ret);
 		if (ret != -EPROBE_DEFER)
 			DRM_ERROR("Failed to get core clock: %d\n", ret);
 		return ret;
 	}
 	dpi->pixel_clock = devm_clk_get(dev, "pixel");
 	if (IS_ERR(dpi->pixel_clock)) {
 		ret = PTR_ERR(dpi->pixel_clock);
+		dev_err(dev, "DPI pixel clock error: %d\n", ret);
 		if (ret != -EPROBE_DEFER)
 			DRM_ERROR("Failed to get pixel clock: %d\n", ret);
 		return ret;
@@ -331,8 +349,10 @@ static int vc4_dpi_bind(struct device *dev, struct device *master, void *data)
 	drm_encoder_helper_add(dpi->encoder, &vc4_dpi_encoder_helper_funcs);
 
 	ret = vc4_dpi_init_bridge(dpi);
-	if (ret)
+	if (ret) {
+		dev_err(dev, "DPI bridge init error: %d\n", ret);
 		goto err_destroy_encoder;
+	}
 
 	dev_set_drvdata(dev, dpi);