Re: Using PCI config space to indicate config location

On Fri, Oct 12, 2012 at 08:59:36AM +1030, Rusty Russell wrote:

quoted

quoted

For writes, the standard seems to be a commit latch.  We could abuse the
generation count for this: the driver writes to it to commit config
changes.

I think this will work. There are a couple of things that bother me:

This assumes read accesses have no side effects, and these are sometimes handy.
Also the semantics for write aren't very clear to me.
I guess device must buffer data until generation count write?
This assumes the device has a buffer to store writes,
and it must track each byte written. I kind of dislike this
tracking of accessed bytes. Also, device would need to resolve conflicts
if any in some device specific way.

It should be trivial to implement: you keep a scratch copy of the config
space, and copy it to the master copy when they hit the latch.

Implementation of this will show whether I've missed anything here, I
think.

What I refer to: what happens if driver does:
- write offset 1
- write offset 3
- hit commit latch

?

-- 
MST