[pmbusplus] userspace i2c, pmbus interactions

[Alex Qiu]

> I think I have tested this and it worked, but it was long ago. My recollection was hwmon and other drivers lock the i2c per transaction, not the driver loads/opens and keeps it locked. But I am not an expert here, so I could be wrong.
IIRC, some function like i2c_master_xfer() in the kernel locks the bus. PMBus Page register and the following register access sits above this layer, so they are not protected by a single lock, and this is where a userspace process can interrupt and cause trouble as Mike pointed out.

- Alex Qiu