Support for Hydra i2c

[Michel Lanners]

On  28 Apr, this message from Benjamin Herrenschmidt echoed through cyberspace:
[snip]
> On non-CHRP PowerMacs, there is at least one I2C bus (maybe more) driven
> by Cuda. It's used for things like planB video input,

Not that it matters much, but for correctness: the Apple planb ASIC
includes its own I2C bus interface, controlling the I2C bus on which
the video decoder chip is connected.

By the way, this I2C interface is quite simple: write a (sub)address,
write a value, and off it goes. However, it seems to be hardcoded to
access only the SAA7196 video decoder, and reading that chip is done
with a different interface.

Which gives me another thought, completely unrelated to the subject of
this mail: I'm wondering whether the video output chips in the 8x00
also have I2C, and if yes, how they are accessed...

> and maybe some more stuffs.

The only device on this I2C bus in the PCI Macs that I know off is the
RADACAL RAMDAC/CLUT (used at least with the control chip), which gets
its timebase factors via I2C.

> Unfortunately, I think we only know how to write to the i2c bus.

Yes.

> More hacking needed before we can implement this one too.

One problem might be that there is as yet no readable device on the bus
;-).

Michel

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