[Cbe-oss-dev] IOC translation & firmware question

[Benjamin Herrenschmidt]

> I believe that breaks with old DD2 boards that have only 512MB of RAM
> and are booted with yaboot instead of netboot, because those may
> not have set up the IOC correctly. Hartmut, can you confirm that?
> 
> I don't think we care much about those old boards any more, but
> if they break, we should document it somewhere.

But DMA should work with the IOC translation completely off, that's my
point. The default storage attributes for when translations are off are
just what we need and that would allow us to shave a bit of performance
of DMA transfers when we have less than 2Gb of RAM (which is the case
all the time).

Maybe I'll add code to explicitely turn off translation when booting
with iommu off , just to be sane whatever the firmware does :-)

The only thing that indeed, I overlooked is that "window at 512M"
thingy, but that's fixable by simply adjusting the offset I use for
direct mapped DMA. I'll have a look.

Cheers,
Ben.