什么是fbtft

fbtft在github中的介绍是“ Linux Framebuffer drivers for small TFT LCD display modules，翻译过来就是支持小型TFT LCD显示器的Linux FrameBuffer驱动。也就是专门为小型TFT LCD所写的Framebuffer驱动。

github地址为：notro/fbtft

wiki地址为：notro/wiki

从fbtft的github上看，fbtft不在更新到github了，迁移到了Linux kernel staging tree。在https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/tree/drivers/staging/fbtft?h=staging-testing中看到fbtft所支持的设备有：

fbtft在STM32MP15X中

在STM32MP1X的4.19内核源码中，fbtft源码在内核根目录的：drivers\staging\fbtft。

如何使用

我手上有st7735r跟Ili9341的屏，看了下fbtft里面的源码正好有st7735r跟Ili9341驱动，先试下st7735r的屏，

在文件drivers\staging\fbtft\fb_st7735r.c中：

static struct fbtft_display display = {
    .regwidth = 8,
    .width = 128,
    .height = 160,
    .init_sequence = default_init_sequence,
    .gamma_num = 2,
    .gamma_len = 16,
    .gamma = DEFAULT_GAMMA,
    .fbtftops = {
        .set_addr_win = set_addr_win,
        .set_var = set_var,
        .set_gamma = set_gamma,
    },
};

FBTFT_REGISTER_DRIVER(DRVNAME, "sitronix,st7735r", &display);

FBTFT_REGISTER_DRIVER展开后如下：

#define FBTFT_REGISTER_DRIVER(_name, _compatible, _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 const struct of_device_id dt_ids[] = {                              \
    { .compatible = _compatible },                                     \
    {},                                                                \
};                                                                         \
                                       \
MODULE_DEVICE_TABLE(of, dt_ids);                                           \

有这么条语句：MODULE_DEVICE_TABLE(of, dt_ids); 。也就是说要使用该设备，需要修改设备树。

修改源码

首先在make menuconfig中把fbtft加上：

1、修改设备树

由于我的屏是接在STM32MP157c的SPI5，所以在设备树中spi5下面添加屏的设备数,CS脚接到STM32MP157C的GPIOF 6，DC脚接到GPIOF 3脚，RESET脚接到GPIOD 13，设备数修改为如下：

&spi5 {
    pinctrl-names = "default", "sleep";
    pinctrl-0 = <&spi5_pins_a>;
    pinctrl-1 = <&spi5_sleep_pins_a>;
    cs-gpios = <&gpiof 6 GPIO_ACTIVE_HIGH>;
    status = "okay";

    st7735r@0{
    compatible = "jianda,jd-t18003-t01", "sitronix,st7735r";
    reg = <0>;
    spi-max-frequency = <32000000>;
    dc-gpios = <&gpiof 3 GPIO_ACTIVE_HIGH>;
    reset-gpios = <&gpiod 13 GPIO_ACTIVE_HIGH>;
    rotation = <270>;
    backlight = &backlight;
    };
};

编译并把设备树跟内核更新到板子上，启动，看屏没什么反应，/dev下也没有fb设备，查看spi相关信息：

root@stm32mp1:~# dmesg | grep "spi"
[    1.543185] spi_stm32 44009000.spi: 8 x 8-bit fifo size
[    1.543206] spi_stm32 44009000.spi: 16-bit maximum data frame
[    1.543670] spi_stm32 44009000.spi: registered master spi0
[    1.543900] spi spi0.0: stm32_spi_setup: set gpio86 output high
[    1.543943] spi spi0.0: setup mode 0, 8 bits/w, 32000000 Hz max --> 0
[    1.544232] spi_stm32 44009000.spi: registered child spi0.0
[    1.544245] spi_stm32 44009000.spi: driver initialized
[    2.097755] fb_st7735r spi0.0: buswidth is not set
[    2.102334] fb_st7735r: probe of spi0.0 failed with error -22

有错误，上网查了下资料，觉得可能是没有添加buswidth，在设备树种把buswitch加上：

&spi5 {
    pinctrl-names = "default", "sleep";
    pinctrl-0 = <&spi5_pins_a>;
    pinctrl-1 = <&spi5_sleep_pins_a>;
    cs-gpios = <&gpiof 6 GPIO_ACTIVE_HIGH>;
    status = "okay";

    st7735r@0{
    compatible = "jianda,jd-t18003-t01", "sitronix,st7735r";
    reg = <0>;
    buswidth = <8>;
    spi-max-frequency = <32000000>;
    dc-gpios = <&gpiof 3 GPIO_ACTIVE_HIGH>;
    reset-gpios = <&gpiod 13 GPIO_ACTIVE_HIGH>;
    rotation = <270>;
    backlight = &backlight;
    };
};

重新更新板子上的设备树，上电，可以看到屏幕有白色变黑色，应该是可以了，在/dev下可以看到多了个fb设备:

测试

在屏上显示随机数：

cat /dev/urandom > /dev/fb0