bus-drivers-i2c-spi

总线驱动程序（I2C 和 SPI）

用途

指导 Agent 编写 Linux I2C 和 SPI 客户端驱动程序：总线注册、i2c_transfer / spi_sync、regmap 抽象、总线子节点中的 DT compatible 属性，以及 probe 模式；与 skills/kernel/device-drivers 中的平台 MMIO 驱动程序互为补充。

适用场景

• I2C/SPI 总线上的传感器或 PMIC
• 将裸机 SPI 寄存器读取转换为内核驱动程序
• 使用 regmap 进行多字节寄存器访问
• 调试 -EREMOTEIO 或缺少 ACK 的问题

工作流

1. I2C 客户端驱动程序

#include <linux/i2c.h>
#include <linux/mod_devicetable.h>

static int my_probe(struct i2c_client *client)
{
    struct regmap *map;

    map = devm_regmap_init_i2c(client, &my_regmap_config);
    if (IS_ERR(map))
        return PTR_ERR(map);

    dev_info(&client->dev, "probed at 0x%02x\n", client->addr);
    return 0;
}

static const struct of_device_id my_of_id[] = {
    { .compatible = "vendor,sensor" },
    { }
};
MODULE_DEVICE_TABLE(of, my_of_id);

static const struct i2c_device_id my_id[] = {
    { "mysensor", 0 },
    { }
};
MODULE_DEVICE_TABLE(i2c, my_id);

static struct i2c_driver my_driver = {
    .probe    = my_probe,
    .remove   = my_remove,
    .driver   = { .name = "mysensor", .of_match_table = my_of_id },
    .id_table = my_id,
};
module_i2c_driver(my_driver);

DT 子节点：

i2c1 {
    sensor@48 {
        compatible = "vendor,sensor";
        reg = <0x48>;
    };
};

2. 原始 I2C 传输

u8 reg = 0x0F, val;
struct i2c_msg msgs[] = {
    { .addr = client->addr, .flags = 0,       .len = 1, .buf = &reg },
    { .addr = client->addr, .flags = I2C_M_RD, .len = 1, .buf = &val },
};
ret = i2c_transfer(client->adapter, msgs, 2);

3. SPI 驱动程序

static int spi_probe(struct spi_device *spi)
{
    spi->mode = SPI_MODE_0;
    spi->bits_per_word = 8;
    spi_setup(spi);

    struct spi_transfer t = {
        .tx_buf = tx,
        .rx_buf = rx,
        .len    = len,
    };
    struct spi_message m;
    spi_message_init(&m);
    spi_message_add_tail(&t, &m);
    return spi_sync(spi, &m);
}

static struct spi_driver spi_drv = {
    .probe  = spi_probe,
    .driver = { .name = "my-spi", .of_match_table = my_of_match },
};
module_spi_driver(spi_drv);

4. regmap（寄存器映射的首选方案）

static const struct regmap_config my_regmap_config = {
    .reg_bits   = 8,
    .val_bits   = 8,
    .max_register = 0x7F,
};

regmap_read(map, REG_STATUS, &val);
regmap_write(map, REG_CTRL, CTRL_ENABLE);
regmap_update_bits(map, REG_CTRL, MASK, ENABLE);

5. 调试

i2cdetect -y 1
i2cdump -y 1 0x48
cat /sys/bus/i2c/devices/i2c-1/1-0048/name

6. Agent 用法

/bus-drivers-i2c-spi Write regmap-based driver for I2C PMIC at 0x58

常见问题

症状	原因	修复方法
-EREMOTEIO	NACK — 地址错误	使用 i2cdetect；检查 DT 中的 reg
SPI 模式错误	CPOL/CPHA 不匹配	与数据手册及 spi->mode 保持一致
Probe 延迟	稳压器/时钟供应方尚未就绪	返回 -EPROBE_DEFER
regmap -EIO	16 位与 8 位寄存器不匹配	设置 reg_bits、val_bits
未使用 DMA	小规模 spi_sync 没问题	批量传输使用 spi_sync_transfer

相关技能

• skills/kernel/device-drivers — IRQ、DMA、运行时 PM
• skills/kernel-dev/device-tree — 总线子节点
• skills/baremetal/spi-i2c-baremetal — 寄存器级协议
• skills/kernel-dev/platform-device-model — 驱动程序模型的对应关系
• skills/kernel-dev/writing-char-drivers — 通过字符设备提供传感器