使用Linux内核里的spi屏驱动-fbtft

Linux内核里已经提供spi接口小屏的设备驱动,在内核的配置选项:

make menuconfig ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-

    Device Drivers  --->  
    Graphics support  ---> 
       <*> Support for small TFT LCD display modules  --->
           ... //屏的驱动IC型号
           <*>   FB driver for the ILI9340 LCD Controller   //drivers/video/fbtft/fb_ili9340.c
           <*>   FB driver for the ST7735R LCD Controller  //drivers/video/fbtft/fb_st7735r.c
               ... 
              Module to for adding FBTFT devices      //drivers/video/fbtft/fbtft_device.c

保存退出后,重编内核镜像和编译驱动模块.
使用新内核镜像启动系统后:
加载驱动模块并指定参数, 如型号为ili9340的屏:

modprobe fbtft_device name=adafruit22a gpios="reset:8,dc:7" busnum=0

加载成功后, 会产生一个/dev/fb8设备文件。
修改QT环境变量: export QT_QPA_PLATFORM=linuxfb:fb=/dev/fb8生效后,执行Qt程序,效果如下:
使用Linux内核里的spi屏驱动-fbtft_第1张图片



在内核源码目录里:

[jk@localhost linux-3.4.112]$ vim drivers/video/fbtft/fb
fb_bd663474.c       fb_ili9486.c        fb_ssd1351.c        fbtft-io.c
fb_hx8340bn.c       fb_pcd8544.c        fb_st7735r.c        fbtft-sysfs.c
fb_hx8347d.c        fb_ra8875.c         fbtft-bus.c         fb_tinylcd.c
fb_hx8353d.c        fb_s6d02a1.c        fbtft-core.c        fb_tls8204.c
fb_ili9320.c        fb_s6d1121.c        fbtft_device.c      fb_upd161704.c
fb_ili9325.c        fb_ssd1289.c        fbtft_device.ko     fb_watterott.c
fb_ili9340.c        fb_ssd1306.c        fbtft_device.mod.c  
fb_ili9341.c        fb_ssd1331.c        fbtft.h  

fb_xxxx.c就是具体型号的驱动IC设备驱动:
每个设备驱动源码里都会调用init_display函数用于初始化屏,我们可以根据此函数里设置的寄存器和值,确认屏驱动IC的型号:

static int init_display(struct fbtft_par *par)
{
    ...
    par->fbtftops.reset(par);

    write_reg(par, 0xEF, 0x03, 0x80, 0x02);
    write_reg(par, 0xCF, 0x00 , 0XC1 , 0X30);
    ...
}

每个屏由一个struct fbtft_display对象来描述:

static struct fbtft_display display = {
    .regwidth = 8,
    .width = WIDTH,
    .height = HEIGHT,
    .fbtftops = {
        .init_display = init_display,  //屏的初始化
        .set_addr_win = set_addr_win,  //设置屏的显示开始坐标
        .set_var = set_var,            //设置屏的翻转角度
    },
};
FBTFT_REGISTER_DRIVER(DRVNAME, &display);

调用宏FBTFT_REGISTER_DRIVER后都会产生和注册一个struct spi_driver对象和一个struct platform_driver对象.

#define FBTFT_REGISTER_DRIVER(_name, _display)                             \
                                       \
static int fbtft_driver_probe_spi(struct spi_device *spi)                  \
{                                                                          \
    return fbtft_probe_common(_display, spi, NULL);                    \
}                                                                          \
                                       \
static int fbtft_driver_remove_spi(struct spi_device *spi)                 \
{                                                                          \
    struct fb_info *info = spi_get_drvdata(spi);                       \
                                       \
    return fbtft_remove_common(&spi->dev, info);                       \
}                                                                          \
                                       \
static int fbtft_driver_probe_pdev(struct platform_device *pdev)           \
{                                                                          \
    return fbtft_probe_common(_display, NULL, pdev);                   \
}                                                                          \
                                       \
static int fbtft_driver_remove_pdev(struct platform_device *pdev)          \
{                                                                          \
    struct fb_info *info = platform_get_drvdata(pdev);                 \
                                       \
    return fbtft_remove_common(&pdev->dev, info);                      \
}                                   
static struct spi_driver fbtft_driver_spi_driver = {                       \
    .driver = {                                                        \
        .name   = _name,                                           \
        .owner  = THIS_MODULE,                                     \
    },                                                                 \
    .probe  = fbtft_driver_probe_spi,                                  \
    .remove = fbtft_driver_remove_spi,                                 \
};                                                                         \
                                       \
static struct platform_driver fbtft_driver_platform_driver = {             \
    .driver = {                                                        \
        .name   = _name,                                           \
        .owner  = THIS_MODULE,                                     \
    },                                                                 \
    .probe  = fbtft_driver_probe_pdev,                                 \
    .remove = fbtft_driver_remove_pdev,                                \
};       

static int __init fbtft_driver_module_init(void)                           \
{                                                                          \
    int ret;                                                           \
                                       \
    ret = spi_register_driver(&fbtft_driver_spi_driver);               \
    if (ret < 0)                                                       \
        return ret;                                                \
    return platform_driver_register(&fbtft_driver_platform_driver);    \
}                                                                          \
                                       \
static void __exit fbtft_driver_module_exit(void)                          \
{                                                                          \
    spi_unregister_driver(&fbtft_driver_spi_driver);                   \
    platform_driver_unregister(&fbtft_driver_platform_driver);         \
}                                                                          \
                                       \
module_init(fbtft_driver_module_init);                                     \
module_exit(fbtft_driver_module_exit);

我们可以通过描述spi设备或者平台设备来与屏的设备驱动匹配,但描述设备的参数有点复杂,所以内核里提供了fbtft_device.c,它把我们提供的模块参数,生成相应的spi设备或平台设备,并且提供相关的资源信息.
在fbtft_device.c里,它已定好多的设备名, 每个设备使用一个具体的屏型号:

static struct fbtft_device_display displays[] = {
    {    
        .name = "adafruit18",  //设备名
        .spi = &(struct spi_board_info) {
            .modalias = "fb_st7735r",   //屏的型号
            .max_speed_hz = 32000000,
            .mode = SPI_MODE_0,
            .platform_data = &(struct fbtft_platform_data) {
                .display = {
                    .buswidth = 8, 
                    .backlight = 1, 
                },
                .gpios = (const struct fbtft_gpio []) {
                    { "reset", 25 },
                    { "dc", 24 },
                    { "led", 18 },
                    {},
                },
                .gamma = ADAFRUIT18_GAMMA,
            }
        }
    }, { 
        .name = "adafruit18_green",
        .spi = &(struct spi_board_info) {
            .modalias = "fb_st7735r",
    ...

加载此驱动模块时,除了需要指定设备名外,还需要指定多个参数,具体可以通过modinfo查看:

modinfo /lib/modules/3.4.112/kernel/drivers/video/fbtft/fbtft_device.
ko

常用的模块参数有:
gpios用于指定reset,  dc, led等具体使用哪个iomode用于指定spi使用哪种时序
busnum用于指定使用第几个spi控制器
rotate用于指定翻转角度
name用于指定设备名


如:modprobe fbtft_device name=adafruit22a gpios="reset:8,dc:7" busnum=0 debug=0 rotate=90

   gpios="reset:8,dc:7"表示reset引脚是接在GPIOA(8), dc引脚是接在GPIOA(7)


在头文件里: arch/arm/mach-sunxi/include/mach/gpio.h
    #define SUNXI_PA_BASE   0
    #define GPIOA(n)    (SUNXI_PA_BASE + (n))

    所以得出GPIOA(8)的值是8

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