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107 lines
4.0 KiB
Diff
107 lines
4.0 KiB
Diff
From 24ec4e6211e88c02b925182281cb435f96dbd692 Mon Sep 17 00:00:00 2001
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From: Michael Kaplan <m.kaplan@evva.com>
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Date: Wed, 5 Feb 2020 10:27:23 +0100
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Subject: [PATCH] overlays: add hdmi-backlight-hwhack-gpio-overlay
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This is a Devicetree overlay for GPIO based backlight on/off capability.
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Use this if you have one of those HDMI displays whose backlight cannot be controlled via DPMS over HDMI and plan to do a little soldering to use an RPi gpio pin for on/off switching.
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See: https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
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This was tested with a clone of the Waveshare "7 inch HDMI Touch LCD C" where I soldered two mosfets to override the backlight dip-switch.
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When the overlay is loaded, a sysfs backlight node appears which can be used to modify the brightness value (0 or 1), and is even used by DPMS to switch the display backlight off after the configured timeout.
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(On current Raspbian Buster Desktop, it's also possible to wakeup the display via a tap on the touch display :-) )
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Signed-off-by: Michael Kaplan <m.kaplan@evva.com>
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---
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arch/arm/boot/dts/overlays/Makefile | 1 +
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arch/arm/boot/dts/overlays/README | 14 ++++++
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.../hdmi-backlight-hwhack-gpio-overlay.dts | 47 +++++++++++++++++++
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3 files changed, 62 insertions(+)
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create mode 100644 arch/arm/boot/dts/overlays/hdmi-backlight-hwhack-gpio-overlay.dts
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--- a/arch/arm/boot/dts/overlays/Makefile
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+++ b/arch/arm/boot/dts/overlays/Makefile
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@@ -51,6 +51,7 @@ dtbo-$(CONFIG_ARCH_BCM2835) += \
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gpio-poweroff.dtbo \
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gpio-shutdown.dtbo \
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hd44780-lcd.dtbo \
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+ hdmi-backlight-hwhack-gpio.dtbo \
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hifiberry-amp.dtbo \
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hifiberry-dac.dtbo \
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hifiberry-dacplus.dtbo \
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--- a/arch/arm/boot/dts/overlays/README
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+++ b/arch/arm/boot/dts/overlays/README
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@@ -883,6 +883,20 @@ Params: pin_d4 GPIO pin
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display_width Width of the display in characters
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+Name: hdmi-backlight-hwhack-gpio
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+Info: Devicetree overlay for GPIO based backlight on/off capability.
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+ Use this if you have one of those HDMI displays whose backlight cannot
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+ be controlled via DPMS over HDMI and plan to do a little soldering to
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+ use an RPi gpio pin for on/off switching. See:
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+ https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
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+Load: dtoverlay=hdmi-backlight-hwhack-gpio,<param>=<val>
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+Params: gpio_pin GPIO pin used (default 17)
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+ active_low Set this to 1 if the display backlight is
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+ switched on when the wire goes low.
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+ Leave the default (value 0) if the backlight
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+ expects a high to switch it on.
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+
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+
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Name: hifiberry-amp
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Info: Configures the HifiBerry Amp and Amp+ audio cards
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Load: dtoverlay=hifiberry-amp
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--- /dev/null
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+++ b/arch/arm/boot/dts/overlays/hdmi-backlight-hwhack-gpio-overlay.dts
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@@ -0,0 +1,47 @@
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+/*
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+ * Devicetree overlay for GPIO based backlight on/off capability.
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+ *
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+ * Use this if you have one of those HDMI displays whose backlight cannot be
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+ * controlled via DPMS over HDMI and plan to do a little soldering to use an
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+ * RPi gpio pin for on/off switching.
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+ *
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+ * See: https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
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+ *
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+ */
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+/dts-v1/;
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+/plugin/;
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+
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+/ {
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+ compatible = "brcm,bcm2835";
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+
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+ fragment@1 {
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+ target = <&gpio>;
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+ __overlay__ {
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+ hdmi_backlight_hwhack_gpio_pins: hdmi_backlight_hwhack_gpio_pins {
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+ brcm,pins = <17>;
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+ brcm,function = <1>; /* out */
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+ };
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+ };
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+ };
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+
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+ fragment@2 {
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+ target-path = "/";
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+ __overlay__ {
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+ hdmi_backlight_hwhack_gpio: hdmi_backlight_hwhack_gpio {
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+ compatible = "gpio-backlight";
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+
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+ pinctrl-names = "default";
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+ pinctrl-0 = <&hdmi_backlight_hwhack_gpio_pins>;
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+
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+ gpios = <&gpio 17 0>;
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+ default-on;
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+ };
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+ };
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+ };
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+
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+ __overrides__ {
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+ gpio_pin = <&hdmi_backlight_hwhack_gpio>,"gpios:4",
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+ <&hdmi_backlight_hwhack_gpio_pins>,"brcm,pins:0";
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+ active_low = <&hdmi_backlight_hwhack_gpio>,"gpios:8";
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+ };
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+};
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