[PATCH v3 0/4] drm: Add Support for Passive RGB to VGA bridges

[PATCH v3 0/4] 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 v2:
  - Changed the compatible as suggested
  - Rebased on top 4.8

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 (4):
  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/rgb-to-vga-bridge.txt  |  52 +++++
 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/rgb-to-vga.c                | 232 +++++++++++++++++++++
 7 files changed, 353 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
 create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c

-- 
2.9.3

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[PATCH v3 0/4] 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 v2:
  - Changed the compatible as suggested
  - Rebased on top 4.8

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 (4):
  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/rgb-to-vga-bridge.txt  |  52 +++++
 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/rgb-to-vga.c                | 232 +++++++++++++++++++++
 7 files changed, 353 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
 create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c

-- 
2.9.3

[PATCH v3 1/4] 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.

Acked-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
---
 .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
 drivers/gpu/drm/bridge/Kconfig                     |   6 +
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
 4 files changed, 291 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
 create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c

diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
new file mode 100644
index 000000000000..83a053fb51a0
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
@@ -0,0 +1,52 @@
+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 "rgb-to-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 = "rgb-to-vga-bridge";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	ports {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		port@0 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <0>;
+
+			vga_bridge_in: endpoint {
+				remote-endpoint = <&tcon0_out_vga>;
+			};
+		};
+
+		port@1 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <1>;
+
+			vga_bridge_out: endpoint {
+				remote-endpoint = <&vga_con_in>;
+			};
+		};
+	};
+};
diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
new file mode 100644
index 000000000000..84b1b10198a4
--- /dev/null
+++ b/drivers/gpu/drm/bridge/rgb-to-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 = "rgb-to-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		= "rgb-to-vga-bridge",
+		.of_match_table	= dumb_vga_match,
+	},
+};
+module_platform_driver(dumb_vga_driver);
+
+MODULE_AUTHOR("Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>");
+MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
+MODULE_LICENSE("GPL");
-- 
2.9.3

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[PATCH v3 1/4] 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.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
 drivers/gpu/drm/bridge/Kconfig                     |   6 +
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
 4 files changed, 291 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
 create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c

diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
new file mode 100644
index 000000000000..83a053fb51a0
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
@@ -0,0 +1,52 @@
+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 "rgb-to-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 = "rgb-to-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 {
+				remote-endpoint = <&tcon0_out_vga>;
+			};
+		};
+
+		port at 1 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <1>;
+
+			vga_bridge_out: endpoint {
+				remote-endpoint = <&vga_con_in>;
+			};
+		};
+	};
+};
diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
new file mode 100644
index 000000000000..84b1b10198a4
--- /dev/null
+++ b/drivers/gpu/drm/bridge/rgb-to-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 = "rgb-to-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		= "rgb-to-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");
-- 
2.9.3

[PATCH v3 2/4] 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-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
---
 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..1cc7ff361f49 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 = "rgb-to-vga-bridge";
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		ports {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			port@0 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+				reg = <0>;
+
+				vga_bridge_in: endpoint@0 {
+					reg = <0>;
+					remote-endpoint = <&tcon0_out_vga>;
+				};
+			};
+
+			port@1 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+				reg = <1>;
+
+				vga_bridge_out: endpoint@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@0 {
+		reg = <0>;
+		remote-endpoint = <&vga_bridge_in>;
+	};
+};
+
 &uart1 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&uart1_pins_b>;
-- 
2.9.3

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[PATCH v3 2/4] 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..1cc7ff361f49 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 = "rgb-to-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>;
-- 
2.9.3

[PATCH v3 3/4] 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-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
---
 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 2c8665cd9dc5..22ef41afc658 100644
--- a/arch/arm/configs/multi_v7_defconfig
+++ b/arch/arm/configs/multi_v7_defconfig
@@ -567,6 +567,7 @@ CONFIG_DRM=y
 CONFIG_DRM_I2C_ADV7511=m
 # CONFIG_DRM_I2C_CH7006 is not set
 # CONFIG_DRM_I2C_SIL164 is not set
+CONFIG_DRM_RGB_TO_VGA=m
 CONFIG_DRM_NXP_PTN3460=m
 CONFIG_DRM_PARADE_PS8622=m
 CONFIG_DRM_NOUVEAU=m
-- 
2.9.3

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[PATCH v3 3/4] 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 2c8665cd9dc5..22ef41afc658 100644
--- a/arch/arm/configs/multi_v7_defconfig
+++ b/arch/arm/configs/multi_v7_defconfig
@@ -567,6 +567,7 @@ CONFIG_DRM=y
 CONFIG_DRM_I2C_ADV7511=m
 # CONFIG_DRM_I2C_CH7006 is not set
 # CONFIG_DRM_I2C_SIL164 is not set
+CONFIG_DRM_RGB_TO_VGA=m
 CONFIG_DRM_NXP_PTN3460=m
 CONFIG_DRM_PARADE_PS8622=m
 CONFIG_DRM_NOUVEAU=m
-- 
2.9.3

[PATCH v3 4/4] 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 714da336ec86..d830e258db59 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_RGB_TO_VGA=y
 CONFIG_DRM_SUN4I=y
 CONFIG_FB=y
 CONFIG_FB_SIMPLE=y
-- 
2.9.3

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

[PATCH v3 4/4] 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 714da336ec86..d830e258db59 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_RGB_TO_VGA=y
 CONFIG_DRM_SUN4I=y
 CONFIG_FB=y
 CONFIG_FB_SIMPLE=y
-- 
2.9.3

Re: [PATCH v3 2/4] ARM: sun5i: a13-olinuxino: Enable VGA bridge

[Chen-Yu Tsai]

On Thu, Sep 8, 2016 at 8:17 PM, Maxime Ripard
<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> wrote:
> 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-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>

Assuming the bridge bindings are good,

Acked-by: Chen-Yu Tsai <wens-jdAy2FN1RRM@public.gmane.org>
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[PATCH v3 2/4] ARM: sun5i: a13-olinuxino: Enable VGA bridge

[Chen-Yu Tsai]

On Thu, Sep 8, 2016 at 8:17 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> 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>

Assuming the bridge bindings are good,

Acked-by: Chen-Yu Tsai <wens@csie.org>

Re: [PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Chen-Yu Tsai]

Hi,

On Thu, Sep 8, 2016 at 8:17 PM, Maxime Ripard
<maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> 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.
>
> Acked-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> ---
>  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
>  4 files changed, 291 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
>  create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +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 "rgb-to-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 = "rgb-to-vga-bridge";
> +       #address-cells = <1>;
> +       #size-cells = <0>;
> +
> +       ports {
> +               #address-cells = <1>;
> +               #size-cells = <0>;
> +
> +               port@0 {
> +                       #address-cells = <1>;
> +                       #size-cells = <0>;
> +                       reg = <0>;
> +
> +                       vga_bridge_in: endpoint {
> +                               remote-endpoint = <&tcon0_out_vga>;
> +                       };
> +               };
> +
> +               port@1 {
> +                       #address-cells = <1>;
> +                       #size-cells = <0>;
> +                       reg = <1>;
> +
> +                       vga_bridge_out: endpoint {
> +                               remote-endpoint = <&vga_con_in>;
> +                       };
> +               };
> +       };
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
> new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-vga.c
> @@ -0,0 +1,232 @@

No beginning file header / copyright statement?

> +
> +#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,

drm_modeset_helper_vtables.h says the following about .best_encoder:

    You can leave this function to NULL if the connector is only
    attached to a single encoder and you are using the atomic helpers.
    In this case, the core will call drm_atomic_helper_best_encoder()
    for you.

IMHO you can drop the callback here.

> +};
> +
> +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 = {

const?

> +       .attach         = dumb_vga_attach,
> +       .enable         = dumb_vga_nop,
> +       .disable        = dumb_vga_nop,
> +       .pre_enable     = dumb_vga_nop,
> +       .post_disable   = dumb_vga_nop,

Nit: The 4 nops can be dropped. The header file states these
callbacks are optional.

> +};
> +
> +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 = "rgb-to-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           = "rgb-to-vga-bridge",
> +               .of_match_table = dumb_vga_match,
> +       },
> +};
> +module_platform_driver(dumb_vga_driver);
> +
> +MODULE_AUTHOR("Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>");
> +MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
> +MODULE_LICENSE("GPL");

FWIW the rest looks fine.


Regards
ChenYu
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[PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Chen-Yu Tsai]

Hi,

On Thu, Sep 8, 2016 at 8:17 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> 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.
>
> Acked-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
>  4 files changed, 291 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
>  create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +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 "rgb-to-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 = "rgb-to-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 {
> +                               remote-endpoint = <&tcon0_out_vga>;
> +                       };
> +               };
> +
> +               port at 1 {
> +                       #address-cells = <1>;
> +                       #size-cells = <0>;
> +                       reg = <1>;
> +
> +                       vga_bridge_out: endpoint {
> +                               remote-endpoint = <&vga_con_in>;
> +                       };
> +               };
> +       };
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
> new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-vga.c
> @@ -0,0 +1,232 @@

No beginning file header / copyright statement?

> +
> +#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,

drm_modeset_helper_vtables.h says the following about .best_encoder:

    You can leave this function to NULL if the connector is only
    attached to a single encoder and you are using the atomic helpers.
    In this case, the core will call drm_atomic_helper_best_encoder()
    for you.

IMHO you can drop the callback here.

> +};
> +
> +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 = {

const?

> +       .attach         = dumb_vga_attach,
> +       .enable         = dumb_vga_nop,
> +       .disable        = dumb_vga_nop,
> +       .pre_enable     = dumb_vga_nop,
> +       .post_disable   = dumb_vga_nop,

Nit: The 4 nops can be dropped. The header file states these
callbacks are optional.

> +};
> +
> +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 = "rgb-to-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           = "rgb-to-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");

FWIW the rest looks fine.


Regards
ChenYu

Re: [PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Archit Taneja]

Hi,

On 09/08/2016 05:47 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.

Some minor comments below, besides the ones by ChenYu.

>
> Acked-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>   .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>   drivers/gpu/drm/bridge/Kconfig                     |   6 +
>   drivers/gpu/drm/bridge/Makefile                    |   1 +
>   drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
>   4 files changed, 291 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
>   create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +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 "rgb-to-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 = "rgb-to-vga-bridge";
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;

The above 2 properties required for the individual port nodes, right?

> +			reg = <0>;
> +
> +			vga_bridge_in: endpoint {
> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port@1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint {
> +				remote-endpoint = <&vga_con_in>;
> +			};
> +		};
> +	};
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_VGA
> +	tristate "Dumb RGB to VGA Bridge support"
> +	select DRM_KMS_HELPER

In the current state of the driver, we need to rely on OF support for
it to function properly. I guess we need to depend on CONFIG_OF here.

> +	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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
> new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-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

s/if/in ?

> +	 * the DDC pins, or the I2C bus might be disfunctional.

s/disfunctional/not functional

Looks good otherwise.

Archit

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a Linux Foundation Collaborative Project
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[PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Archit Taneja]

Hi,

On 09/08/2016 05:47 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.

Some minor comments below, besides the ones by ChenYu.

>
> Acked-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>   .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>   drivers/gpu/drm/bridge/Kconfig                     |   6 +
>   drivers/gpu/drm/bridge/Makefile                    |   1 +
>   drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 +++++++++++++++++++++
>   4 files changed, 291 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
>   create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +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 "rgb-to-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 = "rgb-to-vga-bridge";
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port at 0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;

The above 2 properties required for the individual port nodes, right?

> +			reg = <0>;
> +
> +			vga_bridge_in: endpoint {
> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port at 1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint {
> +				remote-endpoint = <&vga_con_in>;
> +			};
> +		};
> +	};
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_VGA
> +	tristate "Dumb RGB to VGA Bridge support"
> +	select DRM_KMS_HELPER

In the current state of the driver, we need to rely on OF support for
it to function properly. I guess we need to depend on CONFIG_OF here.

> +	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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c b/drivers/gpu/drm/bridge/rgb-to-vga.c
> new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-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

s/if/in ?

> +	 * the DDC pins, or the I2C bus might be disfunctional.

s/disfunctional/not functional

Looks good otherwise.

Archit

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

Re: [PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Laurent Pinchart]

Hi Maxime,

Thank you for the patch.

On Thursday 08 Sep 2016 14:17:48 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.
> 
> Acked-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++++
>  4 files changed, 291 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> 
> diff --git
> a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +Passive RGB to VGA bridge
> +-------------------------
> +
> +This binding is aimed for entirely passive RGB to VGA bridges that do not
> +require any configuration.

Couldn't it also support active RGB to VGA bridges that don't require any 
configuration ? It would seem a bit pointless to define a separate DT binding 
for them.

> +Required properties:
> +
> +- compatible: Must be "rgb-to-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 = "rgb-to-vga-bridge";
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <0>;
> +
> +			vga_bridge_in: endpoint {
> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port@1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint {
> +				remote-endpoint = <&vga_con_in>;
> +			};
> +		};
> +	};
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c
> b/drivers/gpu/drm/bridge/rgb-to-vga.c new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-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);

Bridges should really not create connectors. Fixing this problem is a bit out 
of scope for your patch, but I'm concerned that the growing number of bridge 
drivers will make it difficult to fix it later.

> +	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,

Those four operations are optional, you don't need 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 = "rgb-to-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		= "rgb-to-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");

-- 
Regards,

Laurent Pinchart

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dri-devel@lists.freedesktop.org
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[PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Laurent Pinchart]

Hi Maxime,

Thank you for the patch.

On Thursday 08 Sep 2016 14:17:48 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.
> 
> Acked-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
>  drivers/gpu/drm/bridge/Kconfig                     |   6 +
>  drivers/gpu/drm/bridge/Makefile                    |   1 +
>  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++++
>  4 files changed, 291 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> 
> diff --git
> a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> new file mode 100644
> index 000000000000..83a053fb51a0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,52 @@
> +Passive RGB to VGA bridge
> +-------------------------
> +
> +This binding is aimed for entirely passive RGB to VGA bridges that do not
> +require any configuration.

Couldn't it also support active RGB to VGA bridges that don't require any 
configuration ? It would seem a bit pointless to define a separate DT binding 
for them.

> +Required properties:
> +
> +- compatible: Must be "rgb-to-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 = "rgb-to-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 {
> +				remote-endpoint = <&tcon0_out_vga>;
> +			};
> +		};
> +
> +		port at 1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			vga_bridge_out: endpoint {
> +				remote-endpoint = <&vga_con_in>;
> +			};
> +		};
> +	};
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b590e678052d..42b95adf5091 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_RGB_TO_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 efdb07e878f5..3bb8cbe09fe9 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_RGB_TO_VGA) += rgb-to-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/rgb-to-vga.c
> b/drivers/gpu/drm/bridge/rgb-to-vga.c new file mode 100644
> index 000000000000..84b1b10198a4
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-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);

Bridges should really not create connectors. Fixing this problem is a bit out 
of scope for your patch, but I'm concerned that the growing number of bridge 
drivers will make it difficult to fix it later.

> +	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,

Those four operations are optional, you don't need 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 = "rgb-to-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		= "rgb-to-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");

-- 
Regards,

Laurent Pinchart

Re: [PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Laurent Pinchart]

On Sunday 18 Sep 2016 13:01:16 Laurent Pinchart wrote:
> On Thursday 08 Sep 2016 14:17:48 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.
> > 
> > Acked-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> > Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> > ---
> > 
> >  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
> >  drivers/gpu/drm/bridge/Kconfig                     |   6 +
> >  drivers/gpu/drm/bridge/Makefile                    |   1 +
> >  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++
> >  4 files changed, 291 insertions(+)
> >  create mode 100644
> > 
> > Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > new file mode 100644
> > index 000000000000..83a053fb51a0
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > @@ -0,0 +1,52 @@
> > +Passive RGB to VGA bridge
> > +-------------------------
> > +
> > +This binding is aimed for entirely passive RGB to VGA bridges that do not
> > +require any configuration.
> 
> Couldn't it also support active RGB to VGA bridges that don't require any
> configuration ? It would seem a bit pointless to define a separate DT
> binding for them.

I'm thinking in particular about the ADV7123 
(http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7123.pdf) that already has a DT binding. Would it be feasible to 
combine the two, and support both devices with a single driver ?

> > +Required properties:
> > +
> > +- compatible: Must be "rgb-to-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 = "rgb-to-vga-bridge";
> > +	#address-cells = <1>;
> > +	#size-cells = <0>;
> > +
> > +	ports {
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +
> > +		port@0 {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +			reg = <0>;
> > +
> > +			vga_bridge_in: endpoint {
> > +				remote-endpoint = <&tcon0_out_vga>;
> > +			};
> > +		};
> > +
> > +		port@1 {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +			reg = <1>;
> > +
> > +			vga_bridge_out: endpoint {
> > +				remote-endpoint = <&vga_con_in>;
> > +			};
> > +		};
> > +	};
> > +};

-- 
Regards,

Laurent Pinchart

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[PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Laurent Pinchart]

On Sunday 18 Sep 2016 13:01:16 Laurent Pinchart wrote:
> On Thursday 08 Sep 2016 14:17:48 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.
> > 
> > Acked-by: Rob Herring <robh@kernel.org>
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> > 
> >  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
> >  drivers/gpu/drm/bridge/Kconfig                     |   6 +
> >  drivers/gpu/drm/bridge/Makefile                    |   1 +
> >  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++
> >  4 files changed, 291 insertions(+)
> >  create mode 100644
> > 
> > Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > new file mode 100644
> > index 000000000000..83a053fb51a0
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > @@ -0,0 +1,52 @@
> > +Passive RGB to VGA bridge
> > +-------------------------
> > +
> > +This binding is aimed for entirely passive RGB to VGA bridges that do not
> > +require any configuration.
> 
> Couldn't it also support active RGB to VGA bridges that don't require any
> configuration ? It would seem a bit pointless to define a separate DT
> binding for them.

I'm thinking in particular about the ADV7123 
(http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7123.pdf) that already has a DT binding. Would it be feasible to 
combine the two, and support both devices with a single driver ?

> > +Required properties:
> > +
> > +- compatible: Must be "rgb-to-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 = "rgb-to-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 {
> > +				remote-endpoint = <&tcon0_out_vga>;
> > +			};
> > +		};
> > +
> > +		port at 1 {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +			reg = <1>;
> > +
> > +			vga_bridge_out: endpoint {
> > +				remote-endpoint = <&vga_con_in>;
> > +			};
> > +		};
> > +	};
> > +};

-- 
Regards,

Laurent Pinchart

Re: [PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Maxime Ripard]

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On Sun, Sep 18, 2016 at 01:04:17PM +0300, Laurent Pinchart wrote:
> On Sunday 18 Sep 2016 13:01:16 Laurent Pinchart wrote:
> > On Thursday 08 Sep 2016 14:17:48 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.
> > > 
> > > Acked-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> > > Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> > > ---
> > > 
> > >  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
> > >  drivers/gpu/drm/bridge/Kconfig                     |   6 +
> > >  drivers/gpu/drm/bridge/Makefile                    |   1 +
> > >  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++
> > >  4 files changed, 291 insertions(+)
> > >  create mode 100644
> > > 
> > > Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> > > 
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > new file mode 100644
> > > index 000000000000..83a053fb51a0
> > > --- /dev/null
> > > +++
> > > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > @@ -0,0 +1,52 @@
> > > +Passive RGB to VGA bridge
> > > +-------------------------
> > > +
> > > +This binding is aimed for entirely passive RGB to VGA bridges that do not
> > > +require any configuration.
> > 
> > Couldn't it also support active RGB to VGA bridges that don't require any
> > configuration ? It would seem a bit pointless to define a separate DT
> > binding for them.
> 
> I'm thinking in particular about the ADV7123
> (http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7123.pdf)
> that already has a DT binding.

I guess we don't have the same definition of passive, but I was
thinking of devices that do not need any configuration in order to
operate properly. And this one seems to fall in that category.

> Would it be feasible to combine the two, and support both devices
> with a single driver ?

I don't see why not. But converting the renesas DRM driver seems a bit
out of scope, and the ADV compatible can definitely be added later.

Maxime

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

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[PATCH v3 1/4] drm/bridge: Add RGB to VGA bridge support

[Maxime Ripard]

On Sun, Sep 18, 2016 at 01:04:17PM +0300, Laurent Pinchart wrote:
> On Sunday 18 Sep 2016 13:01:16 Laurent Pinchart wrote:
> > On Thursday 08 Sep 2016 14:17:48 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.
> > > 
> > > Acked-by: Rob Herring <robh@kernel.org>
> > > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > > ---
> > > 
> > >  .../bindings/display/bridge/rgb-to-vga-bridge.txt  |  52 +++++
> > >  drivers/gpu/drm/bridge/Kconfig                     |   6 +
> > >  drivers/gpu/drm/bridge/Makefile                    |   1 +
> > >  drivers/gpu/drm/bridge/rgb-to-vga.c                | 232 ++++++++++++++++
> > >  4 files changed, 291 insertions(+)
> > >  create mode 100644
> > > 
> > > Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > create mode 100644 drivers/gpu/drm/bridge/rgb-to-vga.c
> > > 
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > new file mode 100644
> > > index 000000000000..83a053fb51a0
> > > --- /dev/null
> > > +++
> > > b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> > > @@ -0,0 +1,52 @@
> > > +Passive RGB to VGA bridge
> > > +-------------------------
> > > +
> > > +This binding is aimed for entirely passive RGB to VGA bridges that do not
> > > +require any configuration.
> > 
> > Couldn't it also support active RGB to VGA bridges that don't require any
> > configuration ? It would seem a bit pointless to define a separate DT
> > binding for them.
> 
> I'm thinking in particular about the ADV7123
> (http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7123.pdf)
> that already has a DT binding.

I guess we don't have the same definition of passive, but I was
thinking of devices that do not need any configuration in order to
operate properly. And this one seems to fall in that category.

> Would it be feasible to combine the two, and support both devices
> with a single driver ?

I don't see why not. But converting the renesas DRM driver seems a bit
out of scope, and the ADV compatible can definitely be added later.

Maxime

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