i.MX6ULL 嵌入式 Linux：i2c-imx.c Slave 模式移植实战（Linux 4.9.88）

# 写入 0xAB 到寄存器地址 0x00
i2cset -y 4 0x50 0x00 0xAB

# 读回验证
i2cget -y 4 0x50 0x00
0xab    ✅

cd ~/imx6ull-sdk/Linux-4.9.88
make menuconfig ARCH=arm

# 1. I2C GPIO bitbang master driver (作为 Master 端)
Device Drivers →
  I2C support →
    I2C Hardware Bus support →
      [*] GPIO-based bitbanging I2C (CONFIG_I2C_GPIO)

# 2. I2C Slave support (内核级支持)
Device Drivers →
  I2C support →
    [*] I2C slave support (CONFIG_I2C_SLAVE)

# 3. I2C Slave EEPROM simulator (slave 端测试驱动)
Device Drivers →
  I2C support →
    I2C slave support →
      [*] I2C slave-mode EEPROM simulator (CONFIG_I2C_SLAVE_EEPROM)

# 编译内核和设备树
make ARCH=arm CROSS_COMPILE=~/imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf- zImage dtbs -j4

# 推送到开发板（通过 adb）
adb push arch/arm/boot/zImage /
adb push arch/arm/boot/dts/imx6ull-14x14.dtb /

gpio_i2c: i2c-gpio-0 {
    compatible = "i2c-gpio";
    gpios = <&gpio4 20 GPIO_ACTIVE_HIGH>,     /* SDA = GPIO4_IO20 */
            <&gpio4 21 GPIO_ACTIVE_HIGH>;      /* SCL = GPIO4_IO21 */
    i2c-gpio,delay-us = <100>;
    /* 注意：不加 i2c-gpio,sda-open-drain 和 i2c-gpio,scl-open-drain
       加了会导致驱动使用 gpio_set_value() 推挽输出，slave 无法 ACK
       不加则会使用方向切换模式（INPUT=高阻，OUTPUT LOW=拉低），真正的软件开漏 */
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_gpio_i2c>;
    #address-cells = <1>;
    #size-cells = <0>;
};

pinctrl_gpio_i2c: gpioi2cgrp {
    fsl,pins = <
        MX6UL_PAD_CSI_HSYNC__GPIO4_IO20        0x1b0b0  /* SDA, 47K pull-up, push-pull */
        MX6UL_PAD_CSI_DATA00__GPIO4_IO21       0x1b0b0  /* SCL, 47K pull-up, push-pull */
    >;
};

&i2c1 {
    clock-frequency = <100000>;
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_i2c1>;
    status = "okay";

    /* Slave 设备节点 */
    i2c_slave: i2c-slave@50 {
        compatible = "slave-24c02";     /* 使用内核自带的 slave-eeprom 驱动 */
        reg = <0x50>;
    };
};

pinctrl_i2c1: i2c1grp {
    fsl,pins = <
        MX6UL_PAD_UART4_TX_DATA__I2C1_SCL 0x4001b8b0  /* 开漏+47K上拉 */
        MX6UL_PAD_UART4_RX_DATA__I2C1_SDA 0x4001b8b0  /* 开漏+47K上拉 */
    >;
};

#ifdef CONFIG_I2C_SLAVE
/* spinlock 保护的 ISR → slave_handle 处理 IAAS/ICF 状态机 */
/* hrtimer 30μs 轮询兜底，防止中断不触发时丢失事务 */

/* slave_handle 状态机:
 *
 * I2SR_IAAS=1 (被寻址):
 *   I2SR_SRW=1 → Master 读 → 配置 MTX → 写 I2DR
 *   I2SR_SRW=0 → Master 写 → 清除 MTX → 读 I2DR(虚拟)
 *
 * I2SR_IAAS=0 (数据阶段):
 *   !MTX+ICF  → 收到数据 (WRITE_RECEIVED)
 *   MTX+RXAK  → 收到 ACK (继续发送下一个)
 *   MTX+!RXAK → 收到 NAK (传输结束)
 */
static irqreturn_t i2c_imx_slave_handle(struct imx_i2c_struct *i2c_imx,
                    unsigned int status, unsigned int ctl)
{
    u8 value = 0;
    if (status & I2SR_IAL) { ... }
    if (!(status & I2SR_IBB)) { /* STOP */ return IRQ_HANDLED; }
    if (!(status & I2SR_ICF))  goto out;  /* 传输中，忽略 */
    if (status & I2SR_IAAS) { /* 被寻址 */ ... }
    else if (!(ctl & I2CR_MTX)) { /* 接收数据 */ ... }
    else if (!(status & I2SR_RXAK)) { /* 发送，收到 ACK */ ... }
    else { /* 发送，收到 NAK，结束 */ ... }
out:
    /* 重新调度 hrtimer 30μs 后轮询 */
    hrtimer_try_to_cancel(&i2c_imx->slave_hrtimer);
    hrtimer_forward_now(&i2c_imx->slave_hrtimer, ns_to_ktime(30000));
    hrtimer_restart(&i2c_imx->slave_hrtimer);
    return IRQ_HANDLED;
}
#endif

if (i2c_imx->slave) {
     hrtimer_forward_now(t, ns_to_ktime(30000));
     return HRTIMER_RESTART;
}
return HRTIMER_NORESTART;

# 查看 GPIO 电平状态
cat /sys/kernel/debug/gpio | grep gpio-11[5-8]

# 查看 pinmux 配置
cat /sys/kernel/debug/pinctrl/20e0000.iomuxc/pinmux-pins | grep -E "CSI_HSYNC|CSI_DATA00"

# 查看 pad 电气配置
cat /sys/kernel/debug/pinctrl/20e0000.iomuxc/pinconf-pins | grep -E "pin 120|pin 121"

# 查看 I2C1 寄存器（I2CR, I2SR, IADR）
cat /sys/kernel/debug/regmap/21a0000.i2c/registers 2>/dev/null

# 查看设备树 slave 节点
ls -la /sys/bus/i2c/devices/0-0050/
cat /sys/bus/i2c/devices/0-0050/name

# 查看中断计数
cat /proc/interrupts | grep 21a0

# 查看 I2C1 时钟
cat /sys/kernel/debug/clk/clk_summary | grep i2c1

# 查看 GPC 中断屏蔽状态
# I2C1 IRQ 67, GPC IMR3 bit 3 (67-64=3)

# 正常启动日志
i2c-slave-eeprom 0-0050: i2c_slave_register: client slave flag not set.
    ← 这个警告可以忽略，不影响功能
i2c i2c-0: reg_slave: I2CR=0xc0 I2SR=0x81 IADR=0xa0
    ← I2CR=0xC0 表示 IEN+IIEN，配置正确
i2c i2c-0: I2C slave at 0x50 (aligned)