[PATCH v2 0/7] drm: Add Support for Passive RGB to VGA bridges

[PATCH v2 0/7] drm: Add Support for Passive RGB to VGA bridges

[Maxime Ripard]

Hi,

This serie is about adding support for the RGB to VGA bridge found in
the A13-Olinuxino and the CHIP VGA adapter.

Both these boards rely on an entirely passive bridge made out of
resitor ladders that do not require any initialisation. The only thing
needed is to get the timings from the screen if available (and if not,
fall back on XGA standards), set up the display pipeline to output on
the RGB bus with the proper timings, and you're done.

This serie also fixes a bunch of bugs uncovered when trying to
increase the resolution, and hence the pixel clock, of our
pipeline. It also fixes a few bugs in the DRM driver itself that went
unnoticed before.

Let me know what you think,
Maxime

Changes from v1:
  - Switch to using a vga-connector
  - Use drm_encoder bridge pointer instead of doing our own
  - Report the connector status as unknown instead of connected by
    default, and as connected only if we can retrieve the EDID.
  - Switch to of_i2c_get_adapter by node, and put the reference when done
  - Rebased on linux-next

Maxime Ripard (7):
  drm/sun4i: Store TCON's device structure pointer
  drm/sun4i: Move panel retrieval in RGB connector
  drm/sun4i: Add bridge support
  drm/bridge: Add RGB to VGA bridge support
  ARM: sun5i: a13-olinuxino: Enable VGA bridge
  ARM: multi_v7: enable VGA bridge
  ARM: sunxi: Enable VGA bridge

 .../bindings/display/bridge/dumb-vga.txt           |  54 +++++
 arch/arm/boot/dts/sun5i-a13-olinuxino.dts          |  60 ++++++
 arch/arm/configs/multi_v7_defconfig                |   1 +
 arch/arm/configs/sunxi_defconfig                   |   1 +
 drivers/gpu/drm/bridge/Kconfig                     |   6 +
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/dumb-vga.c                  | 232 +++++++++++++++++++++
 drivers/gpu/drm/sun4i/sun4i_drv.c                  |   4 +-
 drivers/gpu/drm/sun4i/sun4i_rgb.c                  |  64 ++++--
 drivers/gpu/drm/sun4i/sun4i_tcon.c                 |  52 ++++-
 drivers/gpu/drm/sun4i/sun4i_tcon.h                 |   4 +
 11 files changed, 451 insertions(+), 28 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
 create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c

-- 
2.9.0

[PATCH v2 1/7] drm/sun4i: Store TCON's device structure pointer

[Maxime Ripard]

We will need to access TCON's struct device from outside of TCON's driver
bind function. Store it in our private structure.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 1 +
 drivers/gpu/drm/sun4i/sun4i_tcon.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 652385f09735..af136dfc206e 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -446,6 +446,7 @@ static int sun4i_tcon_bind(struct device *dev, struct device *master,
 	dev_set_drvdata(dev, tcon);
 	drv->tcon = tcon;
 	tcon->drm = drm;
+	tcon->dev = dev;
 
 	if (of_device_is_compatible(dev->of_node, "allwinner,sun5i-a13-tcon"))
 		tcon->has_mux = true;
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index 0e0b11db401b..230550b720f1 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -143,6 +143,7 @@
 #define SUN4I_TCON_MAX_CHANNELS		2
 
 struct sun4i_tcon {
+	struct device			*dev;
 	struct drm_device		*drm;
 	struct regmap			*regs;
 
-- 
2.9.0

[PATCH v2 2/7] drm/sun4i: Move panel retrieval in RGB connector

[Maxime Ripard]

In order to properly support bridges and use drm_encoder's bridge pointer,
move the panel (and bridge eventually) retrieval code in the RGB output
init function.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/sun4i/sun4i_rgb.c  | 10 ++++++----
 drivers/gpu/drm/sun4i/sun4i_tcon.c |  8 +-------
 drivers/gpu/drm/sun4i/sun4i_tcon.h |  2 ++
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_rgb.c b/drivers/gpu/drm/sun4i/sun4i_rgb.c
index f5bbac6efb4c..d32f08f9ce5f 100644
--- a/drivers/gpu/drm/sun4i/sun4i_rgb.c
+++ b/drivers/gpu/drm/sun4i/sun4i_rgb.c
@@ -206,15 +206,17 @@ int sun4i_rgb_init(struct drm_device *drm)
 	struct sun4i_rgb *rgb;
 	int ret;
 
-	/* If we don't have a panel, there's no point in going on */
-	if (IS_ERR(tcon->panel))
-		return -ENODEV;
-
 	rgb = devm_kzalloc(drm->dev, sizeof(*rgb), GFP_KERNEL);
 	if (!rgb)
 		return -ENOMEM;
 	rgb->drv = drv;
 
+	tcon->panel = sun4i_tcon_find_panel(tcon->dev->of_node);
+	if (IS_ERR(tcon->panel)) {
+		dev_info(drm->dev, "No panel found... RGB output disabled\n");
+		return 0;
+	}
+
 	drm_encoder_helper_add(&rgb->encoder,
 			       &sun4i_rgb_enc_helper_funcs);
 	ret = drm_encoder_init(drm,
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index af136dfc206e..d2f7489d29a5 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -398,7 +398,7 @@ static int sun4i_tcon_init_regmap(struct device *dev,
 	return 0;
 }
 
-static struct drm_panel *sun4i_tcon_find_panel(struct device_node *node)
+struct drm_panel *sun4i_tcon_find_panel(struct device_node *node)
 {
 	struct device_node *port, *remote, *child;
 	struct device_node *end_node = NULL;
@@ -485,12 +485,6 @@ static int sun4i_tcon_bind(struct device *dev, struct device *master,
 		goto err_free_clocks;
 	}
 
-	tcon->panel = sun4i_tcon_find_panel(dev->of_node);
-	if (IS_ERR(tcon->panel)) {
-		dev_info(dev, "No panel found... RGB output disabled\n");
-		return 0;
-	}
-
 	ret = sun4i_rgb_init(drm);
 	if (ret < 0)
 		goto err_free_clocks;
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index 230550b720f1..4f81d86ee5a4 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -166,6 +166,8 @@ struct sun4i_tcon {
 	struct drm_panel		*panel;
 };
 
+struct drm_panel *sun4i_tcon_find_panel(struct device_node *node);
+
 /* Global Control */
 void sun4i_tcon_disable(struct sun4i_tcon *tcon);
 void sun4i_tcon_enable(struct sun4i_tcon *tcon);
-- 
2.9.0

[PATCH v2 3/7] drm/sun4i: Add bridge support

[Maxime Ripard]

Our RGB bus can be either connected to a bridge or a panel. While the panel
support was already there, the bridge was not.

Fix that.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/gpu/drm/sun4i/sun4i_drv.c  |  4 +--
 drivers/gpu/drm/sun4i/sun4i_rgb.c  | 58 +++++++++++++++++++++++++++++---------
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 43 ++++++++++++++++++++++++++--
 drivers/gpu/drm/sun4i/sun4i_tcon.h |  1 +
 4 files changed, 87 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_drv.c b/drivers/gpu/drm/sun4i/sun4i_drv.c
index 4dc543e1db10..db5ab4d50bd6 100644
--- a/drivers/gpu/drm/sun4i/sun4i_drv.c
+++ b/drivers/gpu/drm/sun4i/sun4i_drv.c
@@ -258,8 +258,8 @@ static int sun4i_drv_add_endpoints(struct device *dev,
 		}
 
 		/*
-		 * If the node is our TCON, the first port is used for our
-		 * panel, and will not be part of the
+		 * If the node is our TCON, the first port is used for
+		 * panel or bridges, and will not be part of the
 		 * component framework.
 		 */
 		if (sun4i_drv_node_is_tcon(node)) {
diff --git a/drivers/gpu/drm/sun4i/sun4i_rgb.c b/drivers/gpu/drm/sun4i/sun4i_rgb.c
index d32f08f9ce5f..d4e52522ec53 100644
--- a/drivers/gpu/drm/sun4i/sun4i_rgb.c
+++ b/drivers/gpu/drm/sun4i/sun4i_rgb.c
@@ -151,7 +151,12 @@ static void sun4i_rgb_encoder_enable(struct drm_encoder *encoder)
 
 	DRM_DEBUG_DRIVER("Enabling RGB output\n");
 
-	drm_panel_enable(tcon->panel);
+	if (!IS_ERR(tcon->panel))
+		drm_panel_enable(tcon->panel);
+
+	if (!IS_ERR(encoder->bridge))
+		drm_bridge_enable(encoder->bridge);
+
 	sun4i_tcon_channel_enable(tcon, 0);
 }
 
@@ -164,7 +169,12 @@ static void sun4i_rgb_encoder_disable(struct drm_encoder *encoder)
 	DRM_DEBUG_DRIVER("Disabling RGB output\n");
 
 	sun4i_tcon_channel_disable(tcon, 0);
-	drm_panel_disable(tcon->panel);
+
+	if (!IS_ERR(encoder->bridge))
+		drm_bridge_disable(encoder->bridge);
+
+	if (!IS_ERR(tcon->panel))
+		drm_panel_disable(tcon->panel);
 }
 
 static void sun4i_rgb_encoder_mode_set(struct drm_encoder *encoder,
@@ -203,6 +213,7 @@ int sun4i_rgb_init(struct drm_device *drm)
 {
 	struct sun4i_drv *drv = drm->dev_private;
 	struct sun4i_tcon *tcon = drv->tcon;
+	struct drm_encoder *encoder;
 	struct sun4i_rgb *rgb;
 	int ret;
 
@@ -210,10 +221,12 @@ int sun4i_rgb_init(struct drm_device *drm)
 	if (!rgb)
 		return -ENOMEM;
 	rgb->drv = drv;
+	encoder = &rgb->encoder;
 
 	tcon->panel = sun4i_tcon_find_panel(tcon->dev->of_node);
-	if (IS_ERR(tcon->panel)) {
-		dev_info(drm->dev, "No panel found... RGB output disabled\n");
+	encoder->bridge = sun4i_tcon_find_bridge(tcon->dev->of_node);
+	if (IS_ERR(tcon->panel) && IS_ERR(encoder->bridge)) {
+		dev_info(drm->dev, "No panel or bridge found... RGB output disabled\n");
 		return 0;
 	}
 
@@ -232,19 +245,36 @@ int sun4i_rgb_init(struct drm_device *drm)
 	/* The RGB encoder can only work with the TCON channel 0 */
 	rgb->encoder.possible_crtcs = BIT(0);
 
-	drm_connector_helper_add(&rgb->connector,
-				 &sun4i_rgb_con_helper_funcs);
-	ret = drm_connector_init(drm, &rgb->connector,
-				 &sun4i_rgb_con_funcs,
-				 DRM_MODE_CONNECTOR_Unknown);
-	if (ret) {
-		dev_err(drm->dev, "Couldn't initialise the rgb connector\n");
-		goto err_cleanup_connector;
+	if (!IS_ERR(tcon->panel)) {
+		drm_connector_helper_add(&rgb->connector,
+					 &sun4i_rgb_con_helper_funcs);
+		ret = drm_connector_init(drm, &rgb->connector,
+					 &sun4i_rgb_con_funcs,
+					 DRM_MODE_CONNECTOR_Unknown);
+		if (ret) {
+			dev_err(drm->dev, "Couldn't initialise the rgb connector\n");
+			goto err_cleanup_connector;
+		}
+
+		drm_mode_connector_attach_encoder(&rgb->connector,
+						  &rgb->encoder);
+
+		ret = drm_panel_attach(tcon->panel, &rgb->connector);
+		if (ret) {
+			dev_err(drm->dev, "Couldn't attach our panel\n");
+			goto err_cleanup_connector;
+		}
 	}
 
-	drm_mode_connector_attach_encoder(&rgb->connector, &rgb->encoder);
+	if (!IS_ERR(encoder->bridge)) {
+		encoder->bridge->encoder = &rgb->encoder;
 
-	drm_panel_attach(tcon->panel, &rgb->connector);
+		ret = drm_bridge_attach(drm, encoder->bridge);
+		if (ret) {
+			dev_err(drm->dev, "Couldn't attach our bridge\n");
+			goto err_cleanup_connector;
+		}
+	}
 
 	return 0;
 
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index d2f7489d29a5..2145ecf2cf5d 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -432,6 +432,40 @@ struct drm_panel *sun4i_tcon_find_panel(struct device_node *node)
 	return of_drm_find_panel(remote) ?: ERR_PTR(-EPROBE_DEFER);
 }
 
+struct drm_bridge *sun4i_tcon_find_bridge(struct device_node *node)
+{
+	struct device_node *port, *remote, *child;
+	struct device_node *end_node = NULL;
+
+	/* Inputs are listed first, then outputs */
+	port = of_graph_get_port_by_id(node, 1);
+
+	/*
+	 * Our first output is the RGB interface where the panel will
+	 * be connected.
+	 */
+	for_each_child_of_node(port, child) {
+		u32 reg;
+
+		of_property_read_u32(child, "reg", &reg);
+		if (reg == 0)
+			end_node = child;
+	}
+
+	if (!end_node) {
+		DRM_DEBUG_DRIVER("Missing bridge endpoint\n");
+		return ERR_PTR(-ENODEV);
+	}
+
+	remote = of_graph_get_remote_port_parent(end_node);
+	if (!remote) {
+		DRM_DEBUG_DRIVER("Enable to parse remote node\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	return of_drm_find_bridge(remote) ?: ERR_PTR(-EPROBE_DEFER);
+}
+
 static int sun4i_tcon_bind(struct device *dev, struct device *master,
 			   void *data)
 {
@@ -514,19 +548,22 @@ static struct component_ops sun4i_tcon_ops = {
 static int sun4i_tcon_probe(struct platform_device *pdev)
 {
 	struct device_node *node = pdev->dev.of_node;
+	struct drm_bridge *bridge;
 	struct drm_panel *panel;
 
 	/*
-	 * The panel is not ready.
+	 * Neither the bridge or the panel is ready.
 	 * Defer the probe.
 	 */
 	panel = sun4i_tcon_find_panel(node);
+	bridge = sun4i_tcon_find_bridge(node);
 
 	/*
 	 * If we don't have a panel endpoint, just go on
 	 */
-	if (PTR_ERR(panel) == -EPROBE_DEFER) {
-		DRM_DEBUG_DRIVER("Still waiting for our panel. Deferring...\n");
+	if ((PTR_ERR(panel) == -EPROBE_DEFER) &&
+	    (PTR_ERR(bridge) == -EPROBE_DEFER)) {
+		DRM_DEBUG_DRIVER("Still waiting for our panel/bridge. Deferring...\n");
 		return -EPROBE_DEFER;
 	}
 
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index 4f81d86ee5a4..100bfa093277 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -166,6 +166,7 @@ struct sun4i_tcon {
 	struct drm_panel		*panel;
 };
 
+struct drm_bridge *sun4i_tcon_find_bridge(struct device_node *node);
 struct drm_panel *sun4i_tcon_find_panel(struct device_node *node);
 
 /* Global Control */
-- 
2.9.0

[PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

[Maxime Ripard]

Some boards have an entirely passive RGB to VGA bridge, based on either
DACs or resistor ladders.

Those might or might not have an i2c bus routed to the VGA connector in
order to access the screen EDIDs.

Add a bridge that doesn't do anything but expose the modes available on the
screen, either based on the EDIDs if available, or based on the XGA
standards.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 .../bindings/display/bridge/dumb-vga.txt           |  54 +++++
 drivers/gpu/drm/bridge/Kconfig                     |   6 +
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/dumb-vga.c                  | 232 +++++++++++++++++++++
 4 files changed, 293 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
 create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c

diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
new file mode 100644
index 000000000000..0056ffa2b31d
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
@@ -0,0 +1,54 @@
+Passive RGB to VGA bridge
+-------------------------
+
+This binding is aimed for entirely passive RGB to VGA bridges that do not
+require any configuration.
+
+Required properties:
+
+- compatible: Must be "dumb-vga-bridge"
+
+Required nodes:
+
+This device has two video ports. Their connections are modeled using the OF
+graph bindings specified in Documentation/devicetree/bindings/graph.txt.
+
+- Video port 0 for RGB input
+- Video port 1 for VGA output
+
+
+Example
+-------
+
+bridge {
+	compatible = "dumb-vga-bridge";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	ports {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		port at 0 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <0>;
+
+			vga_bridge_in: endpoint at 0 {
+				reg = <0>;
+				remote-endpoint = <&tcon0_out_vga>;
+			};
+		};
+
+		port at 1 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <1>;
+
+			vga_bridge_out: endpoint at 0 {
+				reg = <0>;
+				remote-endpoint = <&vga_con_in>;
+			};
+		};
+	};
+};
diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index a141921445f4..4a6560714397 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -17,6 +17,12 @@ config DRM_ANALOGIX_ANX78XX
 	  the HDMI output of an application processor to MyDP
 	  or DisplayPort.
 
+config DRM_DUMB_VGA
+	tristate "Dumb RGB to VGA Bridge support"
+	select DRM_KMS_HELPER
+	help
+	  Support for passive RGB to VGA bridges
+
 config DRM_DW_HDMI
 	tristate
 	select DRM_KMS_HELPER
diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
index bfec9f8cb9d2..413d783828bb 100644
--- a/drivers/gpu/drm/bridge/Makefile
+++ b/drivers/gpu/drm/bridge/Makefile
@@ -1,6 +1,7 @@
 ccflags-y := -Iinclude/drm
 
 obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
+obj-$(CONFIG_DRM_DUMB_VGA) += dumb-vga.o
 obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
 obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
 obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
diff --git a/drivers/gpu/drm/bridge/dumb-vga.c b/drivers/gpu/drm/bridge/dumb-vga.c
new file mode 100644
index 000000000000..c197be591fb6
--- /dev/null
+++ b/drivers/gpu/drm/bridge/dumb-vga.c
@@ -0,0 +1,232 @@
+
+#include <linux/module.h>
+#include <linux/of_graph.h>
+
+#include <drm/drmP.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_crtc_helper.h>
+
+struct dumb_vga {
+	struct drm_bridge	bridge;
+	struct drm_connector	connector;
+
+	struct i2c_adapter	*ddc;
+};
+
+static inline struct dumb_vga *
+drm_bridge_to_dumb_vga(struct drm_bridge *bridge)
+{
+	return container_of(bridge, struct dumb_vga, bridge);
+}
+
+static inline struct dumb_vga *
+drm_connector_to_dumb_vga(struct drm_connector *connector)
+{
+	return container_of(connector, struct dumb_vga, connector);
+}
+
+static int dumb_vga_get_modes(struct drm_connector *connector)
+{
+	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
+	struct edid *edid;
+	int ret;
+
+	if (IS_ERR(vga->ddc))
+		goto fallback;
+
+	edid = drm_get_edid(connector, vga->ddc);
+	if (!edid) {
+		DRM_INFO("EDID readout failed, falling back to standard modes\n");
+		goto fallback;
+	}
+
+	drm_mode_connector_update_edid_property(connector, edid);
+	return drm_add_edid_modes(connector, edid);
+
+fallback:
+	/*
+	 * In case we cannot retrieve the EDIDs (broken or missing i2c
+	 * bus), fallback on the XGA standards
+	 */
+	ret = drm_add_modes_noedid(connector, 1920, 1200);
+
+	/* And prefer a mode pretty much anyone can handle */
+	drm_set_preferred_mode(connector, 1024, 768);
+
+	return ret;
+}
+
+static struct drm_encoder *
+dumb_vga_best_encoder(struct drm_connector *connector)
+{
+	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
+
+	return vga->bridge.encoder;
+}
+
+static struct drm_connector_helper_funcs dumb_vga_con_helper_funcs = {
+	.get_modes	= dumb_vga_get_modes,
+	.best_encoder	= dumb_vga_best_encoder,
+};
+
+static enum drm_connector_status
+dumb_vga_connector_detect(struct drm_connector *connector, bool force)
+{
+	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
+
+	/*
+	 * Even if we have an I2C bus, we can't assume that the cable
+	 * is disconnected if drm_probe_ddc. Some cables don't wire
+	 * the DDC pins, or the I2C bus might be disfunctional.
+	 */
+	if (!IS_ERR(vga->ddc) && drm_probe_ddc(vga->ddc))
+		return connector_status_connected;
+
+	return connector_status_unknown;
+}
+
+static void
+dumb_vga_connector_destroy(struct drm_connector *connector)
+{
+	drm_connector_cleanup(connector);
+}
+
+static struct drm_connector_funcs dumb_vga_con_funcs = {
+	.dpms			= drm_atomic_helper_connector_dpms,
+	.detect			= dumb_vga_connector_detect,
+	.fill_modes		= drm_helper_probe_single_connector_modes,
+	.destroy		= dumb_vga_connector_destroy,
+	.reset			= drm_atomic_helper_connector_reset,
+	.atomic_duplicate_state	= drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state	= drm_atomic_helper_connector_destroy_state,
+};
+
+static int dumb_vga_attach(struct drm_bridge *bridge)
+{
+	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
+	int ret;
+
+	if (!bridge->encoder) {
+		DRM_ERROR("Missing encoder\n");
+		return -ENODEV;
+	}
+
+	drm_connector_helper_add(&vga->connector,
+				 &dumb_vga_con_helper_funcs);
+	ret = drm_connector_init(bridge->dev, &vga->connector,
+				 &dumb_vga_con_funcs, DRM_MODE_CONNECTOR_VGA);
+	if (ret) {
+		DRM_ERROR("Failed to initialize connector\n");
+		return ret;
+	}
+
+	drm_mode_connector_attach_encoder(&vga->connector,
+					  bridge->encoder);
+
+	return 0;
+}
+
+static void dumb_vga_nop(struct drm_bridge *bridge) {};
+
+static struct drm_bridge_funcs dumb_vga_bridge_funcs = {
+	.attach		= dumb_vga_attach,
+	.enable		= dumb_vga_nop,
+	.disable	= dumb_vga_nop,
+	.pre_enable	= dumb_vga_nop,
+	.post_disable	= dumb_vga_nop,
+};
+
+static struct i2c_adapter *dumb_vga_retrieve_ddc(struct device *dev)
+{
+	struct device_node *end_node, *phandle, *remote;
+	struct i2c_adapter *ddc;
+
+	end_node = of_graph_get_endpoint_by_regs(dev->of_node, 1, -1);
+	if (!end_node) {
+		dev_err(dev, "Missing connector endpoint\n");
+		return ERR_PTR(-ENODEV);
+	}
+
+	remote = of_graph_get_remote_port_parent(end_node);
+	of_node_put(end_node);
+	if (!remote) {
+		dev_err(dev, "Enable to parse remote node\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	phandle = of_parse_phandle(remote, "ddc-i2c-bus", 0);
+	of_node_put(remote);
+	if (!phandle)
+		return ERR_PTR(-ENODEV);
+
+	ddc = of_get_i2c_adapter_by_node(phandle);
+	of_node_put(phandle);
+	if (!ddc)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return ddc;
+}
+
+static int dumb_vga_probe(struct platform_device *pdev)
+{
+	struct dumb_vga *vga;
+	int ret;
+
+	vga = devm_kzalloc(&pdev->dev, sizeof(*vga), GFP_KERNEL);
+	if (!vga)
+		return -ENOMEM;
+	platform_set_drvdata(pdev, vga);
+
+	vga->ddc = dumb_vga_retrieve_ddc(&pdev->dev);
+	if (IS_ERR(vga->ddc)) {
+		if (PTR_ERR(vga->ddc) == -ENODEV) {
+			dev_info(&pdev->dev,
+				 "No i2c bus specified... Disabling EDID readout\n");
+		} else {
+			dev_err(&pdev->dev, "Couldn't retrieve i2c bus\n");
+			return PTR_ERR(vga->ddc);
+		}
+	}
+
+	vga->bridge.funcs = &dumb_vga_bridge_funcs;
+	vga->bridge.of_node = pdev->dev.of_node;
+
+	ret = drm_bridge_add(&vga->bridge);
+	if (ret && !IS_ERR(vga->ddc))
+		i2c_put_adapter(vga->ddc);
+
+	return ret;
+}
+
+static int dumb_vga_remove(struct platform_device *pdev)
+{
+	struct dumb_vga *vga = platform_get_drvdata(pdev);
+
+	drm_bridge_remove(&vga->bridge);
+
+	if (!IS_ERR(vga->ddc))
+		i2c_put_adapter(vga->ddc);
+
+	return 0;
+}
+
+static const struct of_device_id dumb_vga_match[] = {
+	{ .compatible = "dumb-vga-bridge" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, dumb_vga_match);
+
+struct platform_driver dumb_vga_driver = {
+	.probe	= dumb_vga_probe,
+	.remove	= dumb_vga_remove,
+	.driver		= {
+		.name		= "dumb-vga-bridge",
+		.of_match_table	= dumb_vga_match,
+	},
+};
+module_platform_driver(dumb_vga_driver);
+
+MODULE_AUTHOR("Maxime Ripard <maxime.ripard@free-electrons.com>");
+MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
+MODULE_LICENSE("GPL");
-- 
2.9.0

[PATCH v2 5/7] ARM: sun5i: a13-olinuxino: Enable VGA bridge

[Maxime Ripard]

Now that we have support for the VGA bridges using our DRM driver, enable
the display engine for the Olimex A13-Olinuxino.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 arch/arm/boot/dts/sun5i-a13-olinuxino.dts | 60 +++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/arch/arm/boot/dts/sun5i-a13-olinuxino.dts b/arch/arm/boot/dts/sun5i-a13-olinuxino.dts
index b3c234c65ea1..1f87b481e9b2 100644
--- a/arch/arm/boot/dts/sun5i-a13-olinuxino.dts
+++ b/arch/arm/boot/dts/sun5i-a13-olinuxino.dts
@@ -72,6 +72,53 @@
 			default-state = "on";
 		};
 	};
+
+	bridge {
+		compatible = "dumb-vga-bridge";
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		ports {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			port at 0 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+				reg = <0>;
+
+				vga_bridge_in: endpoint at 0 {
+					reg = <0>;
+					remote-endpoint = <&tcon0_out_vga>;
+				};
+			};
+
+			port at 1 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+				reg = <1>;
+
+				vga_bridge_out: endpoint at 0 {
+					reg = <0>;
+					remote-endpoint = <&vga_con_in>;
+				};
+			};
+		};
+	};
+
+	vga {
+		compatible = "vga-connector";
+
+		port {
+			vga_con_in: endpoint {
+				remote-endpoint = <&vga_bridge_out>;
+			};
+		};
+	};
+};
+
+&be0 {
+	status = "okay";
 };
 
 &ehci0 {
@@ -211,6 +258,19 @@
 	status = "okay";
 };
 
+&tcon0 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&lcd_rgb666_pins>;
+	status = "okay";
+};
+
+&tcon0_out {
+	tcon0_out_vga: endpoint at 0 {
+		reg = <0>;
+		remote-endpoint = <&vga_bridge_in>;
+	};
+};
+
 &uart1 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&uart1_pins_b>;
-- 
2.9.0

[PATCH v2 6/7] ARM: multi_v7: enable VGA bridge

[Maxime Ripard]

Enable the RGB to VGA bridge driver in the defconfig

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 arch/arm/configs/multi_v7_defconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/configs/multi_v7_defconfig b/arch/arm/configs/multi_v7_defconfig
index 26c35f8b1dd6..edfbd27c9971 100644
--- a/arch/arm/configs/multi_v7_defconfig
+++ b/arch/arm/configs/multi_v7_defconfig
@@ -566,6 +566,7 @@ CONFIG_DRM=y
 CONFIG_DRM_I2C_ADV7511=m
 # CONFIG_DRM_I2C_CH7006 is not set
 # CONFIG_DRM_I2C_SIL164 is not set
+CONFIG_DRM_DUMB_VGA=m
 CONFIG_DRM_NXP_PTN3460=m
 CONFIG_DRM_PARADE_PS8622=m
 CONFIG_DRM_NOUVEAU=m
-- 
2.9.0

[PATCH v2 7/7] ARM: sunxi: Enable VGA bridge

[Maxime Ripard]

Enable the VGA bridge used on the A13-Olinuxino in the sunxi defconfig

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 arch/arm/configs/sunxi_defconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/configs/sunxi_defconfig b/arch/arm/configs/sunxi_defconfig
index 6a1447cf8feb..3676cc2db2eb 100644
--- a/arch/arm/configs/sunxi_defconfig
+++ b/arch/arm/configs/sunxi_defconfig
@@ -98,6 +98,7 @@ CONFIG_MEDIA_RC_SUPPORT=y
 CONFIG_RC_DEVICES=y
 CONFIG_IR_SUNXI=y
 CONFIG_DRM=y
+CONFIG_DRM_DUMB_VGA=y
 CONFIG_DRM_SUN4I=y
 CONFIG_FB=y
 CONFIG_FB_SIMPLE=y
-- 
2.9.0

[PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

[Rob Herring]

On Wed, Jul 20, 2016 at 11:58:54AM +0200, Maxime Ripard wrote:
> Some boards have an entirely passive RGB to VGA bridge, based on either
> DACs or resistor ladders.
> 
> Those might or might not have an i2c bus routed to the VGA connector in
> order to access the screen EDIDs.
> 
> Add a bridge that doesn't do anything but expose the modes available on the
> screen, either based on the EDIDs if available, or based on the XGA
> standards.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  .../bindings/display/bridge/dumb-vga.txt           |  54 +++++
>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>  drivers/gpu/drm/bridge/dumb-vga.c                  | 232 +++++++++++++++++++++
>  4 files changed, 293 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
>  create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> new file mode 100644
> index 000000000000..0056ffa2b31d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> @@ -0,0 +1,54 @@
> +Passive RGB to VGA bridge
> +-------------------------
> +
> +This binding is aimed for entirely passive RGB to VGA bridges that do not
> +require any configuration.
> +
> +Required properties:
> +
> +- compatible: Must be "dumb-vga-bridge"
> +
> +Required nodes:
> +
> +This device has two video ports. Their connections are modeled using the OF
> +graph bindings specified in Documentation/devicetree/bindings/graph.txt.
> +
> +- Video port 0 for RGB input
> +- Video port 1 for VGA output
> +
> +
> +Example
> +-------
> +
> +bridge {
> +	compatible = "dumb-vga-bridge";
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port at 0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <0>;
> +
> +			vga_bridge_in: endpoint at 0 {
> +				reg = <0>;

Don't need a unit address here.

> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port at 1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint at 0 {
> +				reg = <0>;

Ditto.

> +				remote-endpoint = <&vga_con_in>;

Would be good to show the connector node in the example too.

With those changes,

Acked-by: Rob Herring <robh@kernel.org>

[PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

[Archit Taneja]

Hi,

On 07/20/2016 03:28 PM, Maxime Ripard wrote:
> Some boards have an entirely passive RGB to VGA bridge, based on either
> DACs or resistor ladders.
>
> Those might or might not have an i2c bus routed to the VGA connector in
> order to access the screen EDIDs.
>
> Add a bridge that doesn't do anything but expose the modes available on the
> screen, either based on the EDIDs if available, or based on the XGA
> standards.

Our eventual aim is to separate out the connectors from the bridge
drivers wherever possible. In the future, a KMS driver using the
bridge would be responsible for establishing the links between
the bridge and encoder, and the encoder and connector.

If in the future we remove the connector pieces from this driver
to create a separate generic VGA connector driver, we'll end up
with a bridge driver whose main functionality is to convert RGB
signals to VGA. The EDID parts would move to the VGA connector
driver. In your platform's case, there is no software needed
to translate RGB to VGA, but maybe in the future, we might need
to add an optional regulator in the driver to support another
platform. Therefore, the bridge driver would still be handy to
have.

Keeping this in consideration, I think this driver (and the DT
binding) should be called "dumb-rgb-to-vga-bridge", or
"rgb-to-vga-bridge" since that's what the bridge HW primarily
does.

Thanks,
Archit

>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>   .../bindings/display/bridge/dumb-vga.txt           |  54 +++++
>   drivers/gpu/drm/bridge/Kconfig                     |   6 +
>   drivers/gpu/drm/bridge/Makefile                    |   1 +
>   drivers/gpu/drm/bridge/dumb-vga.c                  | 232 +++++++++++++++++++++
>   4 files changed, 293 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
>   create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> new file mode 100644
> index 000000000000..0056ffa2b31d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> @@ -0,0 +1,54 @@
> +Passive RGB to VGA bridge
> +-------------------------
> +
> +This binding is aimed for entirely passive RGB to VGA bridges that do not
> +require any configuration.
> +
> +Required properties:
> +
> +- compatible: Must be "dumb-vga-bridge"
> +
> +Required nodes:
> +
> +This device has two video ports. Their connections are modeled using the OF
> +graph bindings specified in Documentation/devicetree/bindings/graph.txt.
> +
> +- Video port 0 for RGB input
> +- Video port 1 for VGA output
> +
> +
> +Example
> +-------
> +
> +bridge {
> +	compatible = "dumb-vga-bridge";
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port at 0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <0>;
> +
> +			vga_bridge_in: endpoint at 0 {
> +				reg = <0>;
> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port at 1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint at 0 {
> +				reg = <0>;
> +				remote-endpoint = <&vga_con_in>;
> +			};
> +		};
> +	};
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index a141921445f4..4a6560714397 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -17,6 +17,12 @@ config DRM_ANALOGIX_ANX78XX
>   	  the HDMI output of an application processor to MyDP
>   	  or DisplayPort.
>
> +config DRM_DUMB_VGA
> +	tristate "Dumb RGB to VGA Bridge support"
> +	select DRM_KMS_HELPER
> +	help
> +	  Support for passive RGB to VGA bridges
> +
>   config DRM_DW_HDMI
>   	tristate
>   	select DRM_KMS_HELPER
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index bfec9f8cb9d2..413d783828bb 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -1,6 +1,7 @@
>   ccflags-y := -Iinclude/drm
>
>   obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
> +obj-$(CONFIG_DRM_DUMB_VGA) += dumb-vga.o
>   obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
>   obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
>   obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
> diff --git a/drivers/gpu/drm/bridge/dumb-vga.c b/drivers/gpu/drm/bridge/dumb-vga.c
> new file mode 100644
> index 000000000000..c197be591fb6
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/dumb-vga.c
> @@ -0,0 +1,232 @@
> +
> +#include <linux/module.h>
> +#include <linux/of_graph.h>
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_crtc.h>
> +#include <drm/drm_crtc_helper.h>
> +
> +struct dumb_vga {
> +	struct drm_bridge	bridge;
> +	struct drm_connector	connector;
> +
> +	struct i2c_adapter	*ddc;
> +};
> +
> +static inline struct dumb_vga *
> +drm_bridge_to_dumb_vga(struct drm_bridge *bridge)
> +{
> +	return container_of(bridge, struct dumb_vga, bridge);
> +}
> +
> +static inline struct dumb_vga *
> +drm_connector_to_dumb_vga(struct drm_connector *connector)
> +{
> +	return container_of(connector, struct dumb_vga, connector);
> +}
> +
> +static int dumb_vga_get_modes(struct drm_connector *connector)
> +{
> +	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
> +	struct edid *edid;
> +	int ret;
> +
> +	if (IS_ERR(vga->ddc))
> +		goto fallback;
> +
> +	edid = drm_get_edid(connector, vga->ddc);
> +	if (!edid) {
> +		DRM_INFO("EDID readout failed, falling back to standard modes\n");
> +		goto fallback;
> +	}
> +
> +	drm_mode_connector_update_edid_property(connector, edid);
> +	return drm_add_edid_modes(connector, edid);
> +
> +fallback:
> +	/*
> +	 * In case we cannot retrieve the EDIDs (broken or missing i2c
> +	 * bus), fallback on the XGA standards
> +	 */
> +	ret = drm_add_modes_noedid(connector, 1920, 1200);
> +
> +	/* And prefer a mode pretty much anyone can handle */
> +	drm_set_preferred_mode(connector, 1024, 768);
> +
> +	return ret;
> +}
> +
> +static struct drm_encoder *
> +dumb_vga_best_encoder(struct drm_connector *connector)
> +{
> +	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
> +
> +	return vga->bridge.encoder;
> +}
> +
> +static struct drm_connector_helper_funcs dumb_vga_con_helper_funcs = {
> +	.get_modes	= dumb_vga_get_modes,
> +	.best_encoder	= dumb_vga_best_encoder,
> +};
> +
> +static enum drm_connector_status
> +dumb_vga_connector_detect(struct drm_connector *connector, bool force)
> +{
> +	struct dumb_vga *vga = drm_connector_to_dumb_vga(connector);
> +
> +	/*
> +	 * Even if we have an I2C bus, we can't assume that the cable
> +	 * is disconnected if drm_probe_ddc. Some cables don't wire
> +	 * the DDC pins, or the I2C bus might be disfunctional.
> +	 */
> +	if (!IS_ERR(vga->ddc) && drm_probe_ddc(vga->ddc))
> +		return connector_status_connected;
> +
> +	return connector_status_unknown;
> +}
> +
> +static void
> +dumb_vga_connector_destroy(struct drm_connector *connector)
> +{
> +	drm_connector_cleanup(connector);
> +}
> +
> +static struct drm_connector_funcs dumb_vga_con_funcs = {
> +	.dpms			= drm_atomic_helper_connector_dpms,
> +	.detect			= dumb_vga_connector_detect,
> +	.fill_modes		= drm_helper_probe_single_connector_modes,
> +	.destroy		= dumb_vga_connector_destroy,
> +	.reset			= drm_atomic_helper_connector_reset,
> +	.atomic_duplicate_state	= drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state	= drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static int dumb_vga_attach(struct drm_bridge *bridge)
> +{
> +	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
> +	int ret;
> +
> +	if (!bridge->encoder) {
> +		DRM_ERROR("Missing encoder\n");
> +		return -ENODEV;
> +	}
> +
> +	drm_connector_helper_add(&vga->connector,
> +				 &dumb_vga_con_helper_funcs);
> +	ret = drm_connector_init(bridge->dev, &vga->connector,
> +				 &dumb_vga_con_funcs, DRM_MODE_CONNECTOR_VGA);
> +	if (ret) {
> +		DRM_ERROR("Failed to initialize connector\n");
> +		return ret;
> +	}
> +
> +	drm_mode_connector_attach_encoder(&vga->connector,
> +					  bridge->encoder);
> +
> +	return 0;
> +}
> +
> +static void dumb_vga_nop(struct drm_bridge *bridge) {};
> +
> +static struct drm_bridge_funcs dumb_vga_bridge_funcs = {
> +	.attach		= dumb_vga_attach,
> +	.enable		= dumb_vga_nop,
> +	.disable	= dumb_vga_nop,
> +	.pre_enable	= dumb_vga_nop,
> +	.post_disable	= dumb_vga_nop,

We don't need to install nops here, the drm bridge core skips
calling the op if it can't find it.

> +};
> +
> +static struct i2c_adapter *dumb_vga_retrieve_ddc(struct device *dev)
> +{
> +	struct device_node *end_node, *phandle, *remote;
> +	struct i2c_adapter *ddc;
> +
> +	end_node = of_graph_get_endpoint_by_regs(dev->of_node, 1, -1);
> +	if (!end_node) {
> +		dev_err(dev, "Missing connector endpoint\n");
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	remote = of_graph_get_remote_port_parent(end_node);
> +	of_node_put(end_node);
> +	if (!remote) {
> +		dev_err(dev, "Enable to parse remote node\n");
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	phandle = of_parse_phandle(remote, "ddc-i2c-bus", 0);
> +	of_node_put(remote);
> +	if (!phandle)
> +		return ERR_PTR(-ENODEV);
> +
> +	ddc = of_get_i2c_adapter_by_node(phandle);
> +	of_node_put(phandle);
> +	if (!ddc)
> +		return ERR_PTR(-EPROBE_DEFER);
> +
> +	return ddc;
> +}
> +
> +static int dumb_vga_probe(struct platform_device *pdev)
> +{
> +	struct dumb_vga *vga;
> +	int ret;
> +
> +	vga = devm_kzalloc(&pdev->dev, sizeof(*vga), GFP_KERNEL);
> +	if (!vga)
> +		return -ENOMEM;
> +	platform_set_drvdata(pdev, vga);
> +
> +	vga->ddc = dumb_vga_retrieve_ddc(&pdev->dev);
> +	if (IS_ERR(vga->ddc)) {
> +		if (PTR_ERR(vga->ddc) == -ENODEV) {
> +			dev_info(&pdev->dev,
> +				 "No i2c bus specified... Disabling EDID readout\n");
> +		} else {
> +			dev_err(&pdev->dev, "Couldn't retrieve i2c bus\n");
> +			return PTR_ERR(vga->ddc);
> +		}
> +	}
> +
> +	vga->bridge.funcs = &dumb_vga_bridge_funcs;
> +	vga->bridge.of_node = pdev->dev.of_node;
> +
> +	ret = drm_bridge_add(&vga->bridge);
> +	if (ret && !IS_ERR(vga->ddc))
> +		i2c_put_adapter(vga->ddc);
> +
> +	return ret;
> +}
> +
> +static int dumb_vga_remove(struct platform_device *pdev)
> +{
> +	struct dumb_vga *vga = platform_get_drvdata(pdev);
> +
> +	drm_bridge_remove(&vga->bridge);
> +
> +	if (!IS_ERR(vga->ddc))
> +		i2c_put_adapter(vga->ddc);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id dumb_vga_match[] = {
> +	{ .compatible = "dumb-vga-bridge" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, dumb_vga_match);
> +
> +struct platform_driver dumb_vga_driver = {
> +	.probe	= dumb_vga_probe,
> +	.remove	= dumb_vga_remove,
> +	.driver		= {
> +		.name		= "dumb-vga-bridge",
> +		.of_match_table	= dumb_vga_match,
> +	},
> +};
> +module_platform_driver(dumb_vga_driver);
> +
> +MODULE_AUTHOR("Maxime Ripard <maxime.ripard@free-electrons.com>");
> +MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
> +MODULE_LICENSE("GPL");
>

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

[Maxime Ripard]

Hi Archit,

On Thu, Jul 21, 2016 at 03:23:18PM +0530, Archit Taneja wrote:
> Hi,
> 
> On 07/20/2016 03:28 PM, Maxime Ripard wrote:
> >Some boards have an entirely passive RGB to VGA bridge, based on either
> >DACs or resistor ladders.
> >
> >Those might or might not have an i2c bus routed to the VGA connector in
> >order to access the screen EDIDs.
> >
> >Add a bridge that doesn't do anything but expose the modes available on the
> >screen, either based on the EDIDs if available, or based on the XGA
> >standards.
> 
> Our eventual aim is to separate out the connectors from the bridge
> drivers wherever possible. In the future, a KMS driver using the
> bridge would be responsible for establishing the links between
> the bridge and encoder, and the encoder and connector.
> 
> If in the future we remove the connector pieces from this driver
> to create a separate generic VGA connector driver, we'll end up
> with a bridge driver whose main functionality is to convert RGB
> signals to VGA. The EDID parts would move to the VGA connector
> driver. In your platform's case, there is no software needed
> to translate RGB to VGA, but maybe in the future, we might need
> to add an optional regulator in the driver to support another
> platform. Therefore, the bridge driver would still be handy to
> have.
> 
> Keeping this in consideration, I think this driver (and the DT
> binding) should be called "dumb-rgb-to-vga-bridge", or
> "rgb-to-vga-bridge" since that's what the bridge HW primarily
> does.

That works for me. I'll change it and repost.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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