Half-complete kernel interface for waiting on CS completion

[Simon Farnsworth]

Hello,

I've run out of time to work on this, as I have a fix (the unused BO trick)
that's good enough for my needs. I've taken Christian's patches (1 and 2 of
this series) and added the obvious ioctl interface on top, enabling
userspace to wait for a kernel fence *if* the kernel gives it some opaque
tokens (currently the kernel ring and sequence number).

I got stuck trying to work out how to pass those tokens back out of the CS
ioctl. Return value isn't enough, as I have 96 bits of information in my
token (32-bit ring number, 64-bit seqno), so I experimented with adding an
extra chunk that the CS ioctl writes. However, I hit pain trying to work out
what to do when writing to that extra chunk fails - the CS has already been
submitted to hardware here, so returning an error is unfriendly.

As I've got the fix I need (Mesa-dev message "[PATCH] r600g: Use a fake
reloc to sleep for fences"), I can't really justify continuing to work on
this, so I'm putting out what I've got, complete with known problems, in
case someone else gets interested.

--
Simon Farnsworth
Software Engineer
ONELAN Limited
http://www.onelan.com/