在使用F1C100S的時候常常會使用小尺寸的液晶屏，比如市場上比較常見的1.14寸液晶屏，下面我們來為該液晶屏添加驅動。

下面以內核Linux-5.7內核版本，液晶驅動芯片為ST7789V，四線SPI接口為例：(例中液晶引腳接到SPI1上)

注意：SPI總線的SCLK和SDA兩個引腳必須接上拉電阻，10k即可。

這里說明下硬件連接，因為有部分人遇到無法成功問題：

LCD液晶引腳	F1C100S板子
SCLK	PA2
SDA	PA1
CS	GND
RESET	PE7
DC	PE10

１．設備樹中添加SPI節點和ST7789V節點：

        spi0:spi@1c05000 {
           compatible = "allwinner,suniv-spi", "allwinner,sun8i-h3-spi";
            reg = <0x1c05000 0x1000>;
            interrupts = <0xa>;
            clocks = <&ccu CLK_BUS_SPI0>, <&ccu CLK_BUS_SPI0>;
            clock-names = "ahb", "mod";
            resets = <&ccu RST_BUS_SPI0>;
            status = "disabled";
            #address-cells = <1>;
            #size-cells = <0>;
            pinctrl-names = "default";
            pinctrl-0 = <&spi0_pins>;
        };

        spi1:spi@1c06000 {
            compatible = "allwinner,suniv-spi", "allwinner,sun8i-h3-spi";
            reg = <0x1c06000 0x1000>;
            interrupts = <0xb>;
            clocks = <&ccu CLK_BUS_SPI1>, <&ccu CLK_BUS_SPI1>;
            clock-names = "ahb", "mod";
            resets = <&ccu RST_BUS_SPI1>;
            status = "disabled";
            #address-cells = <1>;
            #size-cells = <0>;
            bias-pull-up;
            pinctrl-names = "default";
            pinctrl-0 = <&spi1_pins>;
        };

同時在IO節點中申明引腳定義，如下所示：

pio: pinctrl@1c20800 {
            compatible = "allwinner,suniv-f1c100s-pinctrl";
            reg = <0x01c20800 0x400>;
            interrupts = <38>, <39>, <40>;
            clocks = <&ccu CLK_BUS_PIO>, <&osc24M>, <&osc32k>;
            clock-names = "apb", "hosc", "losc";
            gpio-controller;
            interrupt-controller;
            #interrupt-cells = <3>;
            #gpio-cells = <3>;

            uart0_pe_pins: uart0-pe-pins {
                pins = "PE0", "PE1";
                function = "uart0";
            };
            
            lcd_rgb666_pins: lcd-rgb666-pins {
                pins = "PD0", "PD1", "PD2", "PD3", "PD4",
                       "PD5", "PD6", "PD7", "PD8", "PD9",
                       "PD10", "PD11", "PD12", "PD13", "PD14",
                       "PD15", "PD16", "PD17", "PD18", "PD19",
                       "PD20", "PD21";
                function = "lcd";
            };
            
            mmc0_pins: mmc0-pins {
                pins = "PF0", "PF1", "PF2", "PF3", "PF4", "PF5";
                function = "mmc0";
            };

            spi0_pins: spi0-pins{
                pins = "PC0", "PC1", "PC2", "PC3";
                function = "spi0";
            };

            spi1_pins: spi1-pins{
                pins = "PA2","PA0","PA3","PA1";
                function = "spi1";
            };

        };

在設備樹中添加ST7789V節點：

&spi1 {
    st7789v@0 {
        status = "okay";
        compatible = "sitronix,st7789v";
               reg = <0>;
               spi-max-frequency = <32000000>;　　//最大速度32M
               rotate = <0>;     　　//屏幕旋轉角度
               spi-cpol;　　　　　 //SPI引腳模式
               spi-cpha;　　　　　//SPI引腳模式
               rgb;　　　　　　　 //顏色格式為RGB
               fps = <30>;              //刷新幀數30
               buswidth = <8>;       //總線寬度8位
               reset-gpios = <&pio 4 7 GPIO_ACTIVE_LOW>;  //GPIOE7
               dc-gpios = <&pio 4 10 GPIO_ACTIVE_LOW>;    //GPIOE10
               debug = <0>;
        };
    };  

2.修改drivers/staging/fbtft/fbtft-core.c文件中的gpio申請函數：

這里簡單說下原因：因為在5.2版本之后使用的是另一種方式申請gpio，但是這種方式只是簡單的給出了接口，實際并沒有申請到gpio，因此當不去修改申請方式的時候，即使內核log提示已經申請成功并注冊了驅動，但是實際并沒有，導致液晶屏無法驅動起來。

先添加如下頭文件：

#include <linux/gpio.h>
#include <linux/of_gpio.h>

然后修改兩個函數：

static int fbtft_request_one_gpio(struct fbtft_par *par,
                  const char *name, int index,
                  struct gpio_desc **gpiop)
{
    struct device *dev = par->info->device;
    struct device_node *node = dev->of_node;
    int gpio, flags, ret = 0;
    enum of_gpio_flags of_flags;

    if (of_find_property(node, name, NULL)) {
        gpio = of_get_named_gpio_flags(node, name, index, &of_flags);
        if (gpio == -ENOENT)
            return 0;
        if (gpio == -EPROBE_DEFER)
            return gpio;
        if (gpio < 0) {
            dev_err(dev,
                "failed to get '%s' from DT
", name);
            return gpio;
        }

         //active low translates to initially low 
        flags = (of_flags & OF_GPIO_ACTIVE_LOW) ? GPIOF_OUT_INIT_LOW :
                            GPIOF_OUT_INIT_HIGH;
        ret = devm_gpio_request_one(dev, gpio, flags,
                        dev->driver->name);
        if (ret) {
            dev_err(dev,
                "gpio_request_one('%s'=%d) failed with %d
",
                name, gpio, ret);
            return ret;
        }

        *gpiop = gpio_to_desc(gpio);
        fbtft_par_dbg(DEBUG_REQUEST_GPIOS, par, "%s: '%s' = GPIO%d
",
                            __func__, name, gpio);
    }

    return ret;
}

static int fbtft_request_gpios(struct fbtft_par *par)
{
    int i;
    int ret;

    ret = fbtft_request_one_gpio(par, "reset-gpios", 0, &par->gpio.reset);
    if (ret)
        return ret;
    ret = fbtft_request_one_gpio(par, "dc-gpios", 0, &par->gpio.dc);
    if (ret)
        return ret;
    ret = fbtft_request_one_gpio(par, "rd-gpios", 0, &par->gpio.rd);
    if (ret)
        return ret;
    ret = fbtft_request_one_gpio(par, "wr-gpios", 0, &par->gpio.wr);
    if (ret)
        return ret;
    ret = fbtft_request_one_gpio(par, "cs-gpios", 0, &par->gpio.cs);
    if (ret)
        return ret;
    ret = fbtft_request_one_gpio(par, "latch-gpios", 0, &par->gpio.latch);
    if (ret)
        return ret;
    for (i = 0; i < 16; i++) {
        ret = fbtft_request_one_gpio(par, "db-gpios", i,
                         &par->gpio.db[i]);
        if (ret)
            return ret;
        ret = fbtft_request_one_gpio(par, "led-gpios", i,
                         &par->gpio.led[i]);
        if (ret)
            return ret;
        ret = fbtft_request_one_gpio(par, "aux-gpios", i,
                         &par->gpio.aux[i]);
        if (ret)
            return ret;
    }

    return 0;
}

３．由于５.7版本的fbtft復位部分有問題，最后沒有拉高，所以我們需要修改drivers/staging/fbtft/fbtft-core.c中的fbtft_reset函數：

static void fbtft_reset(struct fbtft_par *par)
{
    if (!par->gpio.reset)
        return;
    fbtft_par_dbg(DEBUG_RESET, par, "%s()
", __func__);
    gpiod_set_value_cansleep(par->gpio.reset, 1);
    msleep(10);
    gpiod_set_value_cansleep(par->gpio.reset, 0);
    msleep(200);
    gpiod_set_value_cansleep(par->gpio.reset, 1);
    msleep(10);
}

４．最后由于fbtft提供的ST7789V的初始化代碼部分有問題，導致顏色對不上，因此我們這里使用STM32中的初始化，修改如下：

　　修改drivers/staging/fbtft/fb_st7789v.c中的init_display函數：

static int init_display(struct fbtft_par *par)
{
    par->fbtftops.reset(par);
    mdelay(50);
    write_reg(par,0x36,0x00);
    write_reg(par,0x3A,0x05);
    write_reg(par,0xB2,0x0C,0x0C,0x00,0x33,0x33);
    write_reg(par,0xB7,0x35);
    write_reg(par,0xBB,0x19);
    write_reg(par,0xC0,0x2C);
    write_reg(par,0xC2,0x01);
    write_reg(par,0xC3,0x12);
    write_reg(par,0xC4,0x20);
    write_reg(par,0xC6,0x0F);
    write_reg(par,0xD0,0xA4,0xA1);
    write_reg(par,0xE0,0xD0,0x04,0x0D,0x11,0x13,0x2B,0x3F,0x54,0x4C,0x18,0x0D,0x0B,0x1F,0x23);
    write_reg(par,0xE1,0xD0,0x04,0x0C,0x11,0x13,0x2C,0x3F,0x44,0x51,0x2F,0x1F,0x1F,0x20,0x23);
    write_reg(par,0x21);
    write_reg(par,0x11);
    mdelay(50);
    write_reg(par,0x29);
    mdelay(200);
    return 0;
}

由于FC1000S的SPI中有一個BUG，因此我們在開啟SPI驅動的時候必須選擇A31（Device Drivers -> SPI support）如圖所示：

現在選擇ST7789V驅動并編譯進內核中，如下：

Device Drivers --->　　

　　　　[*] Staging drivers --->　　

　　　　　　　　<*> Support for small TFT LCD display modules --->

　　　　　　　　　　　　　　<*> FB driver for the ST7789V LCD Controller

最后make -j4編譯鏡像：

總結

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