I2C 在 u-boot 上面，有直接操作 I2C 的函数

// drivers/i2c/i2c_core.c// 设置在哪个 I2C bus 上工作
276 int i2c_set_bus_num(unsigned int bus)
277 {
278     int max;
279
280     if ((bus == I2C_BUS) && (I2C_ADAP->init_done > 0))
281         return 0;
282
283 #ifndef CONFIG_SYS_I2C_DIRECT_BUS
284     if (bus >= CONFIG_SYS_NUM_I2C_BUSES)
285         return -1;
286 #endif
287
288     max = ll_entry_count(struct i2c_adapter, i2c);
289     if (I2C_ADAPTER(bus) >= max) {
290         printf("Error, wrong i2c adapter %d max %d possible\n",
291                I2C_ADAPTER(bus), max);
292         return -2;
293     }
294
295 #ifndef CONFIG_SYS_I2C_DIRECT_BUS
296     i2c_mux_disconnect_all();
297 #endif
298
299     gd->cur_i2c_bus = bus;
300     if (I2C_ADAP->init_done == 0)
301         i2c_init_bus(bus, I2C_ADAP->speed, I2C_ADAP->slaveaddr);
302
303 #ifndef CONFIG_SYS_I2C_DIRECT_BUS
304     i2c_mux_set_all();
305 #endif
306     return 0;
307 }
//etc     i2c_set_bus_num(1);//  i2c slave 匹配
313 int i2c_probe(uint8_t chip)
314 {
315     return I2C_ADAP->probe(I2C_ADAP, chip);
316 }
// etc  i2c_probe(0x68)
//  返回是否成功， 0 表示成功 ， 非 0 表示失败// i2c  读写 写
330 int i2c_read(uint8_t chip, unsigned int addr, int alen,
331                 uint8_t *buffer, int len)
332 {
333     return I2C_ADAP->read(I2C_ADAP, chip, addr, alen, buffer, len);
334 }
335
336 int i2c_write(uint8_t chip, unsigned int addr, int alen,
337                 uint8_t *buffer, int len)
338 {
339     return I2C_ADAP->write(I2C_ADAP, chip, addr, alen, buffer, len);
340 }//etc uchar wri_data = 0x3f, red_data;90     if (i2c_write(0x68, 1, 1, (uchar *)&wri_data, sizeof(int)))91         puts("write error\n");9293     if (i2c_read(0x68, 1, 1, (uchar *)&red_data,94              sizeof(int))) {95         puts("Could not read the MCU; something fundamentally"96             " wrong on the I2C bus.\n");97         return -EIO;98     }