Backlight control signal

The ConnectCore 8X SBC Pro uses MIPI-DSI0 PWM as the backlight for the LVDS0 and MIPI-DSI1 PWM as the backlight for the LVDS1.

Kernel configuration

You can manage the backlight support through the following kernel configuration options:

  • Low-level backlight controls (CONFIG_BACKLIGHT_CLASS_DEVICE)

  • Generic PWM-based backlight driver (CONFIG_BACKLIGHT_PWM)

These options are enabled as built-in on the default ConnectCore 8X kernel configuration file.

Besides these, you must also enable support for the PWM. See Pulse-width Modulation (PWM).

Device tree bindings and customization

The PWM backlight interface bindings is documented at Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt.

LVDS backlight

This device tree excerpt shows the three blocks that configure the backlight signal:

  • A backlight entry that uses the generic PWM backlight driver, defines a period for the signal and a table of predefined brightness levels.

  • The enabling of the PWM interface.

  • The IOMUX of the pad, to make it behave as PWM signal (this IOMUX is driven by the display driver).

ConnectCore 8X SBC Pro device tree
	lvds_backlight0: lvds_backlight@0 {
		compatible = "pwm-backlight";
		pwms = <&pwm_mipi_lvds0 0 100000 0>;

		brightness-levels = < 0  1  2  3  4  5  6  7  8  9
				     10 11 12 13 14 15 16 17 18 19
				     20 21 22 23 24 25 26 27 28 29
				     30 31 32 33 34 35 36 37 38 39
				     40 41 42 43 44 45 46 47 48 49
				     50 51 52 53 54 55 56 57 58 59
				     60 61 62 63 64 65 66 67 68 69
				     70 71 72 73 74 75 76 77 78 79
				     80 81 82 83 84 85 86 87 88 89
				     90 91 92 93 94 95 96 97 98 99
				    100>;
		default-brightness-level = <80>;
		power-supply = <&reg_5v_display>;
		status = "okay";
	};

	...

&pwm_mipi_lvds0 {
	status = "okay";
};

	...

	pinctrl_lvds0: lvds0grp {
		fsl,pins = <
			/* LVDS0 touch interrupt */
			SC_P_QSPI0B_DATA2_LSIO_GPIO3_IO20	0x06000020
			/* LVDS0 PWM backlight */
			SC_P_MIPI_DSI0_GPIO0_00_MIPI_DSI0_PWM0_OUT	0x00000020
		>;
	};

See also