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rpi_display: add backlight driver and overlay
Add a mailbox-driven backlight controller for the Raspberry Pi DSI touchscreen display. Requires updated GPU firmware to recognise the mailbox request. Signed-off-by: Gordon Hollingworth <[email protected]>
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‎arch/arm/boot/dts/overlays/Makefile

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@@ -38,6 +38,7 @@ dtb-$(RPI_DT_OVERLAYS) += pps-gpio-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += pwm-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += pwm-2chan-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += raspidac3-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += rpi-backlight-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += rpi-dac-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += rpi-display-overlay.dtb
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dtb-$(RPI_DT_OVERLAYS) += rpi-ft5406-overlay.dtb

‎arch/arm/boot/dts/overlays/README

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@@ -463,6 +463,12 @@ Load: dtoverlay=raspidac3
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Params: <None>
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Name: rpi-backlight
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Info: Raspberry Pi official display backlight driver
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Load: dtoverlay=rpi-backlight
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Params: <None>
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Name: rpi-dac
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Info: Configures the RPi DAC audio card
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Load: dtoverlay=rpi-dac

‎arch/arm/boot/dts/overlays/rpi-backlight-overlay.dts

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@@ -0,0 +1,21 @@
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/*
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* Devicetree overlay for mailbox-driven Raspberry Pi DSI Display
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* backlight controller
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*/
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/dts-v1/;
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/plugin/;
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/ {
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compatible = "brcm,bcm2708";
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fragment@0 {
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target-path = "/";
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__overlay__ {
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rpi_backlight: rpi_backlight {
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compatible = "raspberrypi,rpi-backlight";
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firmware = <&firmware>;
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status = "okay";
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};
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};
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};
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};

‎arch/arm/configs/bcm2709_defconfig

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@@ -801,6 +801,7 @@ CONFIG_FB_UDL=m
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CONFIG_FB_SSD1307=m
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CONFIG_FB_RPISENSE=m
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# CONFIG_BACKLIGHT_GENERIC is not set
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CONFIG_BACKLIGHT_RPI=m
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CONFIG_BACKLIGHT_GPIO=m
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CONFIG_FRAMEBUFFER_CONSOLE=y
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CONFIG_LOGO=y

‎arch/arm/configs/bcmrpi_defconfig

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@@ -794,6 +794,7 @@ CONFIG_FB_UDL=m
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CONFIG_FB_SSD1307=m
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CONFIG_FB_RPISENSE=m
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# CONFIG_BACKLIGHT_GENERIC is not set
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CONFIG_BACKLIGHT_RPI=m
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CONFIG_BACKLIGHT_GPIO=m
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CONFIG_FRAMEBUFFER_CONSOLE=y
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CONFIG_LOGO=y

‎drivers/video/backlight/Kconfig

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@@ -265,6 +265,12 @@ config BACKLIGHT_PWM
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If you have a LCD backlight adjustable by PWM, say Y to enable
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this driver.
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config BACKLIGHT_RPI
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tristate "Raspberry Pi display firmware driven backlight"
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help
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If you have the Raspberry Pi DSI touchscreen display, say Y to
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enable the mailbox-controlled backlight driver.
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config BACKLIGHT_DA903X
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tristate "Backlight Driver for DA9030/DA9034 using WLED"
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depends on PMIC_DA903X

‎drivers/video/backlight/Makefile

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@@ -50,6 +50,7 @@ obj-$(CONFIG_BACKLIGHT_PANDORA) += pandora_bl.o
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obj-$(CONFIG_BACKLIGHT_PCF50633) += pcf50633-backlight.o
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obj-$(CONFIG_BACKLIGHT_PM8941_WLED) += pm8941-wled.o
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obj-$(CONFIG_BACKLIGHT_PWM) += pwm_bl.o
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obj-$(CONFIG_BACKLIGHT_RPI) += rpi_backlight.o
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obj-$(CONFIG_BACKLIGHT_SAHARA) += kb3886_bl.o
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obj-$(CONFIG_BACKLIGHT_SKY81452) += sky81452-backlight.o
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obj-$(CONFIG_BACKLIGHT_TOSA) += tosa_bl.o

‎drivers/video/backlight/rpi_backlight.c

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/*
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* rpi_bl.c - Backlight controller through VPU
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/backlight.h>
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#include <linux/err.h>
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#include <linux/fb.h>
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#include <linux/gpio.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/of.h>
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#include <linux/of_gpio.h>
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#include <linux/platform_device.h>
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#include <linux/slab.h>
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#include <soc/bcm2835/raspberrypi-firmware.h>
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struct rpi_backlight {
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struct device *dev;
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struct device *fbdev;
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struct rpi_firmware *fw;
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};
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static int rpi_backlight_update_status(struct backlight_device *bl)
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{
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struct rpi_backlight *gbl = bl_get_data(bl);
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int brightness = bl->props.brightness;
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int ret;
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if (bl->props.power != FB_BLANK_UNBLANK ||
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bl->props.fb_blank != FB_BLANK_UNBLANK ||
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bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
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brightness = 0;
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ret = rpi_firmware_property(gbl->fw,
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RPI_FIRMWARE_FRAMEBUFFER_SET_BACKLIGHT,
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&brightness, sizeof(brightness));
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if (ret) {
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dev_err(gbl->dev, "Failed to set brightness\n");
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return ret;
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}
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if (brightness < 0) {
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dev_err(gbl->dev, "Backlight change failed\n");
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return -EAGAIN;
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}
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return 0;
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}
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static const struct backlight_ops rpi_backlight_ops = {
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.options = BL_CORE_SUSPENDRESUME,
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.update_status = rpi_backlight_update_status,
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};
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static int rpi_backlight_probe(struct platform_device *pdev)
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{
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struct backlight_properties props;
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struct backlight_device *bl;
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struct rpi_backlight *gbl;
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struct device_node *fw_node;
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gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
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if (gbl == NULL)
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return -ENOMEM;
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gbl->dev = &pdev->dev;
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fw_node = of_parse_phandle(pdev->dev.of_node, "firmware", 0);
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if (!fw_node) {
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dev_err(&pdev->dev, "Missing firmware node\n");
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return -ENOENT;
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}
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gbl->fw = rpi_firmware_get(fw_node);
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if (!gbl->fw)
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return -EPROBE_DEFER;
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memset(&props, 0, sizeof(props));
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props.type = BACKLIGHT_RAW;
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props.max_brightness = 255;
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bl = devm_backlight_device_register(&pdev->dev, dev_name(&pdev->dev),
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&pdev->dev, gbl, &rpi_backlight_ops,
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&props);
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if (IS_ERR(bl)) {
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dev_err(&pdev->dev, "failed to register backlight\n");
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return PTR_ERR(bl);
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}
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bl->props.brightness = 255;
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backlight_update_status(bl);
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platform_set_drvdata(pdev, bl);
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return 0;
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}
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static const struct of_device_id rpi_backlight_of_match[] = {
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{ .compatible = "raspberrypi,rpi-backlight" },
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(of, rpi_backlight_of_match);
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static struct platform_driver rpi_backlight_driver = {
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.driver = {
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.name = "rpi-backlight",
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.of_match_table = of_match_ptr(rpi_backlight_of_match),
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},
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.probe = rpi_backlight_probe,
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};
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module_platform_driver(rpi_backlight_driver);
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MODULE_AUTHOR("Gordon Hollingworth <[email protected]>");
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MODULE_DESCRIPTION("Raspberry Pi mailbox based Backlight Driver");
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MODULE_LICENSE("GPL");

‎include/soc/bcm2835/raspberrypi-firmware.h

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@@ -112,6 +112,7 @@ enum rpi_firmware_property_tag {
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RPI_FIRMWARE_FRAMEBUFFER_SET_OVERSCAN = 0x0004800a,
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RPI_FIRMWARE_FRAMEBUFFER_SET_PALETTE = 0x0004800b,
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RPI_FIRMWARE_FRAMEBUFFER_SET_VSYNC = 0x0004800e,
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RPI_FIRMWARE_FRAMEBUFFER_SET_BACKLIGHT = 0x0004800f,
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RPI_FIRMWARE_VCHIQ_INIT = 0x00048010,
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