Ingo,
     Attached is a patch for 51-28 which brings PPC
up to date for 2.6.12 PREEMPT_RT.  My goal was to
get a more recent vintage of this work building and
minimally booting for PPC.  Yet this has been stable
even under our internal stress tests.  We now have
this running on 8560 and 8260 PPC targets with a few
others in the pipe.

Remaining are a few known BUG asserts to address,
but as we've historically been chasing seemingly
PPC-specific (or perhaps usage-specific) problems in
a fairly old code base it seemed high time to move
forward.  I've also applied the same patch to 51-33
which not being very far from 51-28 did apply clean,
builds, boots, and appears equally stable as 51-28.

In the process of producing the patch I stumbled
across a change introduced in 51-15 where in the
case of PREEMPT_RT it appears hw_irq_controller.end()
is never being called at the end of do_hardirq().
This appears to be an oversight in the code and
the existing PPC openpic code does register a end()
handler which it expects to be called in order to
terminate the interrupt.  Otherwise interrupts at
the current level are effectively disabled.

There is also what I suspect to be some "leaking"
of the __RAW_LOCAL_ILLEGAL_MASK bit out of the
local_irq*() API primitives as the *flags argument.
This may subsequently be used by non-local_irq*()
primitives and wind up unintentionally setting the
__RAW_LOCAL_ILLEGAL_MASK bit in the machine control
register with unpredictable results.

Lastly there is a problem I've yet to isolate
in kernel/printk.c:release_console_sem() where
the expansion of spin_unlock_irq(&logbuf_lock)
generating a call to __raw_local_irq_enable()
will lockup console output on PPC.  In the
interim this has been reverted to a spin_unlock()
call for the case of PREEMPT_RT && PPC.

Feedback, comments welcome.

-john

-- 
john.cooper@timesys.com