Re: I/O write ordering

Grant Grundler
2004-09-23T04:26:33Z

On Thu, Sep 23, 2004 at 01:40:02PM +1000, Benjamin Herrenschmidt wrote:
> Sounds good, though may be a bit tricky to deal with for things where
> both the kernel and the device are fiddling at the same time, like
> the USB OHCI shared area, or ethernet descriptors...

Normally, "ownership" determines access to particular chunks
of shared data. Ie the programming model makes it clear when the
CPU can modify data and when the CPU is done modifying data.
At a minimum, the host and/or device has to know when it
lost a race to modify or access data.
If there are race conditions in the programming model, iomb()
will not fix them.

> But it makes
> sense. Could probably be built on top of the dma_consistent_sync... &
> friends actually if driver used the properly (which they don't as
> nobody really understand their semantics).

Or maybe the other way around?
ie find a better replacement for dma_consistent_sync()?
But that's a different rat hole that needs to be hashed out
on linux-ppc list...or some other place far away from me. :^)

thanks,
grant