Re: i2c and indirect vs. direct config

[Paul Goyette <paul%whooppee.com@localhost>]

On Thu, 31 May 2018, Jason Thorpe wrote:

> I spent some time reviewing NXP’s i2c spec this evening (well, 
> during timeouts, etc. — GO DUBS), and I’m becoming convinced that 
> there is a subtle error in our i2c_bitbang code… the spec seems 
> pretty clear that a START-address-ACK should occur if a device is 
> really there, and thus the “quick read” method for device 
> detection should work 100% of the time. ...

There is at least one i2c bus controller that explicitly doesn't handle 
"quick" transactions - the imc controller built into the Intel X99 
chip-set.  The docs are pretty clear that it implements an absolute 
minimum subset of i2c, just barely enough to talk to the SPD ROMs on 
memory DIMMs.



+------------------+--------------------------+----------------------------+
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:          |
| (Retired)        | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com   |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+