[IMX6Q][Android5.1]移植笔记 --- LCD背光控制

platform: imx6q

os: Android Lollipop 5.1

branch: l5.1.1_2.1.0-ga

LCD 背光的使能通过GPIO高低电平来控制, 因此本文也可以作为GPIO基本控制的一个例子。

硬件部分:

这里是MB_LCD_BL引脚，原理图如下：

最终对应的是KEY_COL4:

对应的GPIO是GPIO4_IO14:

软件部分：

因此此引脚会与UART5功能复用，所以需要移除掉UART5的配置避免冲突

dts配置部分

[kris@:~/myandroid/kernel_imx]$ g  df
diff --git a/arch/arm/boot/dts/eco/imx6qdl-sabresd.dtsi b/arch/arm/boot/dts/ecoimx6qdl-sabresd.dtsi
index efe0335..62ac4a2 100644
--- a/arch/arm/boot/dts/ecoimx6qdl-sabresd.dtsi
+++ b/arch/arm/boot/dts/ecoimx6qdl-sabresd.dtsi
@@ -103,6 +103,11 @@
                status = "disabled";
        };
 
+       /*Kris,20160324, add display power control.*/
+       display_power_ctrl {
+               bl_power_gpio = <&gpio4 14 1>;
+       };
+
        mxcfb2: fb@1 {
                compatible = "fsl,mxc_sdc_fb";
                disp_dev = "hdmi";
@@ -408,6 +413,7 @@
                                MX6QDL_PAD_NANDF_CS1__GPIO6_IO14 0x80000000
                                MX6QDL_PAD_NANDF_CS2__GPIO6_IO15 0x80000000
                                MX6QDL_PAD_NANDF_CS3__GPIO6_IO16 0x80000000
+                               MX6QDL_PAD_KEY_COL4__GPIO4_IO14 0x80000000
                        >;
                };
 
@@ -559,15 +565,6 @@
                };
         /*Kris, 20160310, Use uart2 as console. }*/
       
-               pinctrl_uart5_1: uart5grp-1 {
-                       fsl,pins = <
-                               MX6QDL_PAD_KEY_COL1__UART5_TX_DATA      0x1b0b1
-                               MX6QDL_PAD_KEY_ROW1__UART5_RX_DATA      0x1b0b1
-                               MX6QDL_PAD_KEY_COL4__UART5_RTS_B        0x1b0b1
-                               MX6QDL_PAD_KEY_ROW4__UART5_CTS_B        0x1b0b1
-                       >;
-               };
-
                pinctrl_uart5dte_1: uart5dtegrp-1 {
                        fsl,pins = <
                                MX6QDL_PAD_KEY_ROW1__UART5_TX_DATA      0x1b0b1
@@ -729,13 +726,6 @@
 };
 /*Kris, 20160310, Use uart2 as console. }*/
 
-&uart5 {
-    pinctrl-names = "default";
-    pinctrl-0 = <&pinctrl_uart5_1>;
-    fsl,uart-has-rtscts;
-    status = "okay";
-};
-
 &usbh1 {

diff --git a/arch/arm/boot/dts/imx6qdl.dtsi b/arch/arm/boot/dts/imx6qdl.dtsi
index 047aecc..12a84fb 100644
--- a/arch/arm/boot/dts/imx6qdl.dtsi
+++ b/arch/arm/boot/dts/imx6qdl.dtsi
@@ -36,7 +36,6 @@
                serial1 = &uart2;
                serial2 = &uart3;
                serial3 = &uart4;
-               serial4 = &uart5;
                spi0 = &ecspi1;
                spi1 = &ecspi2;
                spi2 = &ecspi3;

注意：MX6QDL_PAD_KEY_COL4__GPIO4_IO14 0x80000000 这行不配置有可能导致GPIO无法拉高。

源文件部分

diff --git a/arch/arm/mach-imx/mach-imx6q.c b/arch/arm/mach-imx/mach-imx6q.c
index 405889c..35f3abf 100644
--- a/arch/arm/mach-imx/mach-imx6q.c
+++ b/arch/arm/mach-imx/mach-imx6q.c
@@ -349,6 +349,24 @@ static void __init imx6q_mini_pcie_init(void)
        }
 }
 
+static void __init display_power_init(void)
+{
+       struct device_node *lcd = NULL;
+       int ret, bl_power_gpio;
+
+       lcd = of_find_node_by_name(NULL, "display_power_ctrl");
+       if (!lcd)
+               return;
+       bl_power_gpio = of_get_named_gpio(lcd, "bl_power_gpio", 0);
+       if (gpio_is_valid(bl_power_gpio)) {
+               ret = gpio_request_one(bl_power_gpio, GPIOF_OUT_INIT_HIGH,
+                       "bl_power_gpio");
+               pr_info("request bl_power_gpio\n");
+               if (ret)
+                       pr_warn("failed to request bl_power_gpio\n");
+       }
+}
+
 static void __init imx6q_csi_mux_init(void)
 {
        /*
@@ -432,6 +450,9 @@ static void __init imx6q_init_machine(void)
        imx6q_csi_mux_init();
        cpu_is_imx6q() ?  imx6q_pm_init() : imx6dl_pm_init();
        imx6q_mini_pcie_init();
+
+       //Kris
+       display_power_init();
 }

参考：
http://www.kosagi.com/w/index.php?title=Definitive_GPIO_guide

https://community.freescale.com/message/529415

https://community.freescale.com/thread/323719