Geode SC1100 i2c bus

[M. Warner Losh]

In message: <200702042135.25962.freebsd-hackers at dino.sk>
            Milan Obuch <freebsd-hackers at dino.sk> writes:
: On Sunday 04 February 2007 21:21, M. Warner Losh wrote:
: > In message: <200702040918.37825.freebsd-hackers at dino.sk>
: >
: >             Milan Obuch <freebsd-hackers at dino.sk> writes:
: > : On Sunday 04 February 2007 01:21, perryh at pluto.rain.com wrote:
: > : > > > The ACB is at the same level than Uart, so I had a look at sio
: > : > > > source and got a big headache. I'm not really used to drivers
: > : > > > nor kernel programming stuff, that's why I need your help.
: > : > >
: > : > > Why do you compare ACB and UART? In FreeBSD, sio is serial i/o
: > : > > controller, not superIO, maybe you are confused... ACB and UART
: > : > > does not have much in common...
: > : >
: > : > As I read the OP, both the ACB and the serial are in the same chip
: > : > (the superIO), so it would seem reasonable to expect that the method
: > : > of accessing the device registers in the (currently unsupported) ACB
: > : > might be similar to the method of accessing the device registers in
: > : > the (supported) serial port.
: > :
: > : You are right from the point of view 'how to access registers'. But what
: > : OP wrote could be understand another way, too - he tried to modify sio to
: > : create acb driver, which would not achieve the correct results. There is
: > : i2c infrastructure in FreeBSD, acb driver should fit into its place there
: > : and it is not that easy - I tried to understand it, but nobody could/was
: > : willing to/did not care to help me understand it.
: >
: > I'm happy to help you understand it.
: >
: > Warner
: >
: 
: Great, I will go through the code and will ask. What made me not achieve 
: progress was lack of docs - this area is, ehm, under-documented, and lack of 
: description in pcf, the only i2c hardware controller in source tree 
: currently.

pcf isn't the only i2c hardware controller in the tree.  I personally
comitted at91_twi.c quite some time ago.

: Correct me, if I am wrong and there are more - but not smbus, they
: are not the same thing, even if very near to each other. SMbus
: controller in FreeBSD does not expose i2c device to userland, as far
: as I read it, but this was some time ago.

smbus has a higher level interface than i2c, so doesn't expose i2c to
userland because it can't.

: I need some time to prepare myself, but I would like to get this working. 
: There are some projects waiting for it...

Sure thing.  Like I said, I've done a lot with i2c in FreeBSD
lately...

Warner