[i2c] mixed-speed I2C system

[Stanley Cai]

>
> What you are trying to do is wrong for your setup. If you have both
> standard-mode and fast-mode slaves on your I2C bus, then you must use
> use standard-mode speed (100 kbps max) to talk to all of them. You can
> only use higher speeds up to 400 kbps if you only have fast-mode I2C
> devices on your bus. Please refer to Table 3 "Communication bit-rates
> in a mixed speed bus system", on page 25 of the I2C 2.1 specification.
>
Jean, thanks for pointing it out. When scanning the bus, the driver
must work under standard mode. But when you find the I2C device which
is able to work under fast-mode, can you use fast-mode to interact
with the specific device? For some I2C devices like PMIC, response
time is critical to us.  Is there any side effects on the device or
others?

Thanks,
-stanley