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

[Maxime Ripard]

Hi Archit,

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

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

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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[PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

[Archit Taneja]

Hi,

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

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

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

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

Thanks,
Archit

>
> Signed-off-by: Maxime Ripard 
> ---
>   .../bindings/display/bridge/dumb-vga.txt   |  54 +
>   drivers/gpu/drm/bridge/Kconfig |   6 +
>   drivers/gpu/drm/bridge/Makefile|   1 +
>   drivers/gpu/drm/bridge/dumb-vga.c  | 232 
> +
>   4 files changed, 293 insertions(+)
>   create mode 100644 
> Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
>   create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c
>
> diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt 
> b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> new file mode 100644
> index ..0056ffa2b31d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
> @@ -0,0 +1,54 @@
> +Passive RGB to VGA bridge
> +-
> +
> +This binding is aimed for entirely passive RGB to VGA bridges that do not
> +require any configuration.
> +
> +Required properties:
> +
> +- compatible: Must be "dumb-vga-bridge"
> +
> +Required nodes:
> +
> +This device has two video ports. Their connections are modeled using the OF
> +graph bindings specified in Documentation/devicetree/bindings/graph.txt.
> +
> +- Video port 0 for RGB input
> +- Video port 1 for VGA output
> +
> +
> +Example
> +---
> +
> +bridge {
> + compatible = "dumb-vga-bridge";
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + ports {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + port at 0 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <0>;
> +
> + vga_bridge_in: endpoint at 0 {
> + reg = <0>;
> + remote-endpoint = <_out_vga>;
> + };
> + };
> +
> + port at 1 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <1>;
> +
> + vga_bridge_out: endpoint at 0 {
> + reg = <0>;
> + remote-endpoint = <_con_in>;
> + };
> + };
> + };
> +};
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index a141921445f4..4a6560714397 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -17,6 +17,12 @@ config DRM_ANALOGIX_ANX78XX
> the HDMI output of an application processor to MyDP
> or DisplayPort.
>
> +config DRM_DUMB_VGA
> + tristate "Dumb RGB to VGA Bridge support"
> + select DRM_KMS_HELPER
> + help
> +   Support for passive RGB to VGA bridges
> +
>   config DRM_DW_HDMI
>   tristate
>   select DRM_KMS_HELPER
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index bfec9f8cb9d2..413d783828bb 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -1,6 +1,7 @@
>   ccflags-y := -Iinclude/drm
>
>   obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
> +obj-$(CONFIG_DRM_DUMB_VGA) += dumb-vga.o
>   obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
>   obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
>   obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
> diff --git a/drivers/gpu/drm/bridge/dumb-vga.c 
> b/drivers/gpu/drm/bridge/dumb-vga.c
> new file mode 100644
> index ..c197be591fb6
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/dumb-vga.c
> @@ -0,0 

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

[Rob Herring]

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

Don't need a unit address here.

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

Ditto.

> + remote-endpoint = <_con_in>;

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

With those changes,

Acked-by: Rob Herring 

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

[Maxime Ripard]

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

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

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

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

diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt 
b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
new file mode 100644
index ..0056ffa2b31d
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
@@ -0,0 +1,54 @@
+Passive RGB to VGA bridge
+-
+
+This binding is aimed for entirely passive RGB to VGA bridges that do not
+require any configuration.
+
+Required properties:
+
+- compatible: Must be "dumb-vga-bridge"
+
+Required nodes:
+
+This device has two video ports. Their connections are modeled using the OF
+graph bindings specified in Documentation/devicetree/bindings/graph.txt.
+
+- Video port 0 for RGB input
+- Video port 1 for VGA output
+
+
+Example
+---
+
+bridge {
+   compatible = "dumb-vga-bridge";
+   #address-cells = <1>;
+   #size-cells = <0>;
+
+   ports {
+   #address-cells = <1>;
+   #size-cells = <0>;
+
+   port at 0 {
+   #address-cells = <1>;
+   #size-cells = <0>;
+   reg = <0>;
+
+   vga_bridge_in: endpoint at 0 {
+   reg = <0>;
+   remote-endpoint = <_out_vga>;
+   };
+   };
+
+   port at 1 {
+   #address-cells = <1>;
+   #size-cells = <0>;
+   reg = <1>;
+
+   vga_bridge_out: endpoint at 0 {
+   reg = <0>;
+   remote-endpoint = <_con_in>;
+   };
+   };
+   };
+};
diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index a141921445f4..4a6560714397 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -17,6 +17,12 @@ config DRM_ANALOGIX_ANX78XX
  the HDMI output of an application processor to MyDP
  or DisplayPort.

+config DRM_DUMB_VGA
+   tristate "Dumb RGB to VGA Bridge support"
+   select DRM_KMS_HELPER
+   help
+ Support for passive RGB to VGA bridges
+
 config DRM_DW_HDMI
tristate
select DRM_KMS_HELPER
diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
index bfec9f8cb9d2..413d783828bb 100644
--- a/drivers/gpu/drm/bridge/Makefile
+++ b/drivers/gpu/drm/bridge/Makefile
@@ -1,6 +1,7 @@
 ccflags-y := -Iinclude/drm

 obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
+obj-$(CONFIG_DRM_DUMB_VGA) += dumb-vga.o
 obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
 obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
 obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
diff --git a/drivers/gpu/drm/bridge/dumb-vga.c 
b/drivers/gpu/drm/bridge/dumb-vga.c
new file mode 100644
index ..c197be591fb6
--- /dev/null
+++ b/drivers/gpu/drm/bridge/dumb-vga.c
@@ -0,0 +1,232 @@
+
+#include 
+#include 
+
+#include 
+#include 
+#include 
+#include 
+
+struct dumb_vga {
+   struct drm_bridge   bridge;
+   struct drm_connectorconnector;
+
+   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