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 at kernel.org>
> Signed-off-by: Maxime Ripard <maxime.ripard at 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 at free-electrons.com>");
> +MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
> +MODULE_LICENSE("GPL");

-- 
Regards,

Laurent Pinchart

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