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

Chen-Yu Tsai wens at csie.org
Sun Sep 11 23:42:50 PDT 2016


Hi,

On Thu, Sep 8, 2016 at 8:17 PM, Maxime Ripard
<maxime.ripard at 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 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.
> +
> +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 at free-electrons.com>");
> +MODULE_DESCRIPTION("Dumb RGB to VGA bridge driver");
> +MODULE_LICENSE("GPL");

FWIW the rest looks fine.


Regards
ChenYu



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