LCD显示移植(LVDS接口)

Platform: IMX6QP

OS: Android Lollipop 5.1

Freescale Branch: l5.1.1_2.1.0-ga

Kernel Branch: 3.14.52

此例LCD用的是LVDS接口，LDB模块。
 移植分两部分:

HW:电源以及GPIO部分。

SW: LCD timing,BPP，分辨率。

HW部分：

LCD有DVDD和AVDD两个电源，原理图如下：

LCD_AVDD受LCD_VDD控制,LCD_VDD受LCD_PWR_EN pin控制。

本来要考虑各个电源以及reset pin的上电时序，本例中LCD硬件模块已经帮我们做好了，

所以只要控制LCD_PWR_EN，那么上电时序就能正常完成。

LCD_PWR_EN对应的GPIO为GPIO_3_0，开机时只要拉高即可。

LCD_VDD的供电来自SYS_5V，它的最终源头是从PMIC MMPF0100的VGEN2,所以

需要设置其电压，其中要注意的是MMPF0100是通过I2C控制的，驱动加载顺序可能

会在LCD模块后面，所以需要调换下驱动加载顺序，让LCD模块晚于PMIC，这样才

能使用regulator 函数接口。

SW部分：

这部分主要根据LCD spec来确定，有分辨率，bpp, timing,如下：

代码实现：

arch/arm/boot/dts/eco/imx6qdl-sabresd.dtsi：

 /*Kris,20160406, Porting lcd driver.*/
 &ldb {
     status = "okay";

     lvds-channel@0 {
         fsl,data-mapping = "spwg";
         fsl,data-width = <24>;
         primary;
         status = "okay";

         display-timings {
             native-mode = <&timing0>;
             timing0: cog_t700mixn {
                 clock-frequency = <50000000>;
                 hactive = <1024>;
                 vactive = <600>;
                 hback-porch = <220>;
                 hfront-porch = <40>;
                 vback-porch = <21>;
                 vfront-porch = <7>;
                 hsync-len = <60>;
                 vsync-len = <10>;
             };
         };
     };
 };

 / {
     /*Kris,20160406, Porting lcd driver.*/
     cog_t700mixn {
         compatible = "cog_t700mixn";
         bl_power_gpio = <&gpio4 14 1>;
         lcd_power_gpio = <&gpio3 0 1>;
         DVDD-supply = <&vgen2_reg>;
     };
 };

   imx6qdl-sabresd {
         pinctrl_hog: hoggrp {
             fsl,pins = <
             ......
                 MX6QDL_PAD_EIM_DA0__GPIO3_IO00  0x80000000
             >;
         };

   mxcfb1: fb@0 {
         compatible = "fsl,mxc_sdc_fb";
         disp_dev = "ldb";
         interface_pix_fmt = "RGB24";
         default_bpp = <32>;
         int_clk = <0>;
         late_init = <0>;
         status = "disabled";
     };

arch/arm/configs/imx_v7_android_defconfig：

 #Kris,20160406, Porting lcd driver.
 CONFIG_COG_T700MIXN=y

drivers/Makefile：

 # regulators early, since some subsystems rely on them to initialize
 obj-$(CONFIG_REGULATOR)     += regulator/

 #Kris,20160406, Porting lcd driver.
 #Load lcd driver after regulator module to wait it to be ready.
 obj-y               += video/

drivers/video/mxc/Kconfig：

 #Kris,20160406, Porting lcd driver.
 config COG_T700MIXN
     bool "COG T700MIXN lcd driver."
     default n

drivers/video/mxc/Makefile：

 #Kris,20160406, Porting lcd driver.
 obj-$(CONFIG_COG_T700MIXN) += cog_t700mixn.o

drivers/video/mxc/cog_t700mixn.c：

 "font-size:14px;">#include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include

 #define DRIVER_NAME "cog-t700mixn"

 static const struct of_device_id t700mixn_dt_ids[] = {
     { .compatible = "cog_t700mixn", },
     { /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, t700mixn_dt_ids);

 static int t700mixn_probe(struct platform_device *pdev)
 {
     static struct regulator *dvdd_regulator;
     struct device_node *lcd = NULL;
     int ret, bl_power_gpio, lcd_power_gpio;

     printk("%s\n", __func__);

     lcd = pdev->dev.of_node;

     //enable backlight power.
     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");
     }

     //Set VGEN2 of pmic.
     dvdd_regulator = devm_regulator_get(&pdev->dev, "DVDD");
     if (!IS_ERR(dvdd_regulator)) {
         regulator_set_voltage(dvdd_regulator,1500000,1500000);
         ret = regulator_enable(dvdd_regulator);
         if (ret) {
             pr_err("%s:DVDD set voltage error\n", __func__);
             return ret;
         } else {
             dev_info(&pdev->dev,"%s:DVDD set voltage ok\n", __func__);
         }
     } else {
         dvdd_regulator = NULL;
         pr_err("%s: cannot get DVDD voltage error\n", __func__);
     }

     //this gpio control DVDD and AVDD together.
     lcd_power_gpio = of_get_named_gpio(lcd, "lcd_power_gpio", 0);
     if (gpio_is_valid(lcd_power_gpio)) {
         ret = gpio_request_one(lcd_power_gpio, GPIOF_OUT_INIT_HIGH,
             "bl_power_gpio");
         pr_info("request lcd_power_gpio\n");
         if (ret)
             pr_warn("failed to request lcd_power_gpio\n");
     }

     return ret;
 }

 static struct platform_driver t700mixn_driver = {
     .probe  = t700mixn_probe,
     .driver = {
         .of_match_table = t700mixn_dt_ids,
         .name   = DRIVER_NAME,
         .owner  = THIS_MODULE,
     },
 };
 module_platform_driver(t700mixn_driver);

 MODULE_AUTHOR("Kris.Fei");
 MODULE_DESCRIPTION("COG T700MIXN lcd driver");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("platform:" DRIVER_NAME);

参考：

kernel/Documentation/devicetree/bindings/staging/imx-drm/ldb.txt

kernel/Documentation/devicetree/bindings/fb/fsl_ipuv3_fb.txt

http://blog.chinaunix.net/uid-20680966-id-3623224.html