[MinnowBoard] i2c support

[John Hawley]

Inline & cutting down as this is getting a little long -JH

On 03/07/2016 02:27 AM, Tony wrote:
> I am not sure, why read fails. It is Minnowboard MAX.

Since it's the MAX you are *LIKELY* running into a level shifter issue,
which is obnoxious.  What device is this?  I'm happy to try and get one
in to double check what's going on if you can let me know what you've got.

> I tried running i2cdetect on bus 7 which fails with error
> 
> "Error: Can't use SMBus Quick Write command on this bus"

The bus itself doesn't support the Quick Write command so you need to
add `-r` to the command line so that it doesn't actually try and do that.

I'll add that info to the wiki (along with my suggestion on the
i2cdetect and which bus you should look for) but some example code that
might be helpful can be found here as well:

https://github.com/MinnowBoard/minnow-max-extras/blob/master/calamari/calamari-i2c-eeprom.sh

> Reading from address also fails
> 
> "sudo i2cget -y 7 0x54 0x0c
> Error: Read failed"
> 
> Can the problem with level shifters be fixed on MAX boards?

If it was the level shifters I'd expect something like "lost bus
arbitration" not an absolute read failed.  Can you try the i2cdtect with
the -r, and that attached, and let me know?  Again it would be helpful
to know what chip, and I'll snag one and get it in.

- John