Re: newbus bus access routines and bus_space_barrier()

Usually they are needed, but we get away without them often because they are needed in a limited set of circumstances and we have memory barriers in our locking primitives.

Warner

On Oct 15, 2011, at 7:48 PM, Adrian Chadd wrote:

Hi all,

I'm not clued up on the way of the bus API, so please excuse the
newbie questions.

Nathan and I found that ath(4) wasn't working for a user because of a
missing bus barrier. Ath trips it up because it does lots of loops of
register reads/writes through the bus stream API rather than the
normal bus API.
It does this because it handles the register value swapping in
hardware rather than in software.

The correct fix is to teach ath(4) to use bus_space_barrier() calls
when doing stream calls, which I can do, but the newbus documentation
points out that both normal and stream bus access doesn't enforce
ordering, and barrier calls are needed. But I don't see lots of
bus_space_barrier() calls everywhere. Why's that?

Thanks,


Adrian
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