[PATCH v5 2/5] drm/bridge: Add RGB to VGA bridge support
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Fri Oct 7 06:42:42 PDT 2016
Hi Maxime,
Thank you for the patch.
On Friday 30 Sep 2016 16:37:06 Maxime Ripard wrote:
> Some boards have an entirely passive RGB to VGA bridge, based on either
> DACs or resistor ladders.
A resistor ladder is a DAC :-)
> 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>
Tested-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Please see below for a few comments.
> ---
> .../bindings/display/bridge/rgb-to-vga-bridge.txt | 48 +++++
> drivers/gpu/drm/bridge/Kconfig | 7 +
> drivers/gpu/drm/bridge/Makefile | 1 +
> drivers/gpu/drm/bridge/rgb-to-vga.c | 229 ++++++++++++++++++
> 4 files changed, 285 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..a8375bc1f9cb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/rgb-to-vga-bridge.txt
> @@ -0,0 +1,48 @@
> +Dumb RGB to VGA bridge
> +----------------------
> +
> +This binding is aimed for dumb 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 {
> + reg = <0>;
> +
> + vga_bridge_in: endpoint {
> + remote-endpoint = <&tcon0_out_vga>;
> + };
> + };
> +
> + port at 1 {
> + 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..d690398c541c 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -17,6 +17,13 @@ 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"
> + depends on OF
> + 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..5ff4d4f3598f
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/rgb-to-vga.c
> @@ -0,0 +1,229 @@
> +/*
> + * Copyright (C) 2015-2016 Free Electrons
> + * Copyright (C) 2015-2016 NextThing Co
> + *
> + * Maxime Ripard <maxime.ripard at free-electrons.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 of
> + * the License, or (at your option) any later version.
> + */
> +
> +#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 const struct drm_connector_helper_funcs dumb_vga_con_helper_funcs =
> { + .get_modes = dumb_vga_get_modes,
> +};
> +
> +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 fails. Some cables don't
> + * wire the DDC pins, or the I2C bus might not be working at
> + * all.
> + */
> + 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 const 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,
You can use drm_connector_cleanup directly here.
> + .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 const struct drm_bridge_funcs dumb_vga_bridge_funcs = {
> + .attach = dumb_vga_attach,
> +};
> +
> +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");
Nitpicking, there's no need for an ellipsis ("..."). I'd write the message as
"DDC not available, disabling EDID readout".
You could also turn it into a dev_dbg() message as I'm not sure it's really
crucial information, that's up to you.
> + } 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",
If we changing the compatible string to "dumb-vga-dac" as proposed by Archit,
let's not forget to rename the driver (dumb-vga-dac.ko seems a good match) as
well as the description string below ("Dumb VGA DAC bridge driver" ?). Both
The DT binding and Kconfig texts need to be updated as well.
I would also rename struct dumb_vga to dumb_vga_dac, that's up to you.
> + .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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