target/linux/bcm27xx/patches-5.4/950-0419-overlays-add-hdmi-backlight-hwhack-gpio-overlay.patch

   1 From c6e4343e441558f45df2685b9ed7c13daf7988be Mon Sep 17 00:00:00 2001
   2 From: Michael Kaplan <m.kaplan@evva.com>
   3 Date: Wed, 5 Feb 2020 10:27:23 +0100
   4 Subject: [PATCH] overlays: add hdmi-backlight-hwhack-gpio-overlay
   5
   6 This is a Devicetree overlay for GPIO based backlight on/off capability.
   7
   8 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.
   9
  10 See: https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
  11
  12 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.
  13 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.
  14 (On current Raspbian Buster Desktop, it's also possible to wakeup the display via a tap on the touch display :-) )
  15
  16 Signed-off-by: Michael Kaplan <m.kaplan@evva.com>
  17 ---
  18  arch/arm/boot/dts/overlays/Makefile           |  1 +
  19  arch/arm/boot/dts/overlays/README             | 14 ++++++
  20  .../hdmi-backlight-hwhack-gpio-overlay.dts    | 47 +++++++++++++++++++
  21  3 files changed, 62 insertions(+)
  22  create mode 100644 arch/arm/boot/dts/overlays/hdmi-backlight-hwhack-gpio-overlay.dts
  23
  24 --- a/arch/arm/boot/dts/overlays/Makefile
  25 +++ b/arch/arm/boot/dts/overlays/Makefile
  26 @@ -51,6 +51,7 @@ dtbo-$(CONFIG_ARCH_BCM2835) += \
  27         gpio-poweroff.dtbo \
  28         gpio-shutdown.dtbo \
  29         hd44780-lcd.dtbo \
  30 +       hdmi-backlight-hwhack-gpio.dtbo \
  31         hifiberry-amp.dtbo \
  32         hifiberry-dac.dtbo \
  33         hifiberry-dacplus.dtbo \
  34 --- a/arch/arm/boot/dts/overlays/README
  35 +++ b/arch/arm/boot/dts/overlays/README
  36 @@ -883,6 +883,20 @@ Params: pin_d4                  GPIO pin
  37          display_width           Width of the display in characters
  38
  39
  40 +Name:   hdmi-backlight-hwhack-gpio
  41 +Info:   Devicetree overlay for GPIO based backlight on/off capability.
  42 +        Use this if you have one of those HDMI displays whose backlight cannot
  43 +        be controlled via DPMS over HDMI and plan to do a little soldering to
  44 +        use an RPi gpio pin for on/off switching. See:
  45 +        https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
  46 +Load:   dtoverlay=hdmi-backlight-hwhack-gpio,<param>=<val>
  47 +Params: gpio_pin                GPIO pin used (default 17)
  48 +        active_low              Set this to 1 if the display backlight is
  49 +                                switched on when the wire goes low.
  50 +                                Leave the default (value 0) if the backlight
  51 +                                expects a high to switch it on.
  52 +
  53 +
  54  Name:   hifiberry-amp
  55  Info:   Configures the HifiBerry Amp and Amp+ audio cards
  56  Load:   dtoverlay=hifiberry-amp
  57 --- /dev/null
  58 +++ b/arch/arm/boot/dts/overlays/hdmi-backlight-hwhack-gpio-overlay.dts
  59 @@ -0,0 +1,47 @@
  60 +/*
  61 + * Devicetree overlay for GPIO based backlight on/off capability.
  62 + *
  63 + * Use this if you have one of those HDMI displays whose backlight cannot be
  64 + * controlled via DPMS over HDMI and plan to do a little soldering to use an
  65 + * RPi gpio pin for on/off switching.
  66 + *
  67 + * See: https://www.waveshare.com/wiki/7inch_HDMI_LCD_(C)#Backlight_Control
  68 + *
  69 + */
  70 +/dts-v1/;
  71 +/plugin/;
  72 +
  73 +/ {
  74 +       compatible = "brcm,bcm2835";
  75 +
  76 +       fragment@1 {
  77 +               target = <&gpio>;
  78 +               __overlay__ {
  79 +                       hdmi_backlight_hwhack_gpio_pins: hdmi_backlight_hwhack_gpio_pins {
  80 +                               brcm,pins = <17>;
  81 +                               brcm,function = <1>; /* out */
  82 +                       };
  83 +               };
  84 +       };
  85 +
  86 +       fragment@2 {
  87 +               target-path = "/";
  88 +               __overlay__ {
  89 +                       hdmi_backlight_hwhack_gpio: hdmi_backlight_hwhack_gpio {
  90 +                               compatible = "gpio-backlight";
  91 +
  92 +                               pinctrl-names = "default";
  93 +                               pinctrl-0 = <&hdmi_backlight_hwhack_gpio_pins>;
  94 +
  95 +                               gpios = <&gpio 17 0>;
  96 +                               default-on;
  97 +                       };
  98 +               };
  99 +       };
 100 +
 101 +       __overrides__ {
 102 +               gpio_pin   = <&hdmi_backlight_hwhack_gpio>,"gpios:4",
 103 +                            <&hdmi_backlight_hwhack_gpio_pins>,"brcm,pins:0";
 104 +               active_low = <&hdmi_backlight_hwhack_gpio>,"gpios:8";
 105 +       };
 106 +};