I2C_BUFSTAT
[I2C_BUFSTAT] = 0x40,
[I2C_BUFSTAT] = 0xc0,
fifodepth = I2C_BUFSTAT_FIFODEPTH(I2C_READ_REG(sc, I2C_BUFSTAT));
len = I2C_READ_REG(sc, I2C_BUFSTAT);
len = I2C_READ_REG(sc, I2C_BUFSTAT);