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[Qemu-devel] Determining interest in PPC e500spin, yield, and openpic pa

From: alarson
Subject: [Qemu-devel] Determining interest in PPC e500spin, yield, and openpic patches
Date: Mon, 13 Jun 2016 18:08:30 -0500

We've used older versions of QEMU for several years as a virtual
target for our OS.  Many thanks to the community for providing this

We've been working to get our OS running under QEMU 2.x and have
identified a few bugs in QEMU, have made some enhancements, and are
still tracking down some other curious behaviors.  I'm looking for
some guidance as to how, and whether, you'd like patches for the

1. There is a defect in ppce500_spin.c:spin_kick() that creates an
   incorrectly sized TLB entry.  This was reported as bug
   https://bugs.launchpad.net/qemu/+bug/1587535  I can provide a
   patch if desired.

2. We have implemented the PPC "yield" instruction.  I can provide a
   patch if desired.

3. We're working on support for openpic timers.  We're not finished,
   but it would be helpful to know if a patch is desired or if we
   should expect to maintain the changes independently.

4. We're currently tracking down why in our e500 (both unicore and
   multi-core) PPC QEMU 2.5 guest (x86 host), that with interrupts
   disabled, after enabling the decrementer and issuing a "wait"
   instruction QEMU continues to "busy loop", consuming an entire host
   CPU doing apparently nothing.  As expected, issuing a "wait" prior
   to enabling the decrementer leaves the host process idle.  We found
   the bug in the PPC "wait" instruction implementation that was
   independently reported and resolved last week, but that did not fix
   the problem.  We also have our OS running on the g3beige and using
   MSR.POW which causes the host to "sleep", but we are having no joy
   with e500 and "wait".  Any pointers would be appreciated.  When we
   find something we'll report back.

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