Subject: Re: [PATCH] powerpc: add denormalisation exception handling for POWER6/7

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 12 Jul 2011 14:12:04 +1000

On Mon, 2011-07-11 at 22:51 -0500, Kumar Gala wrote:
> On Jul 11, 2011, at 12:52 AM, Michael Neuling wrote:
> 
> > On POWER6 and POWER7 if the input operand to an instruction is a
> > denormalised single precision binary floating we can take a
> > denormalisation exception where it's expected that the hypervisor (HV=1)
> > will fix up the inputs before the instruction is run.
> > 
> > This adds code to handle this denormalisation exception for POWER6 and
> > POWER7.
> > 
> > It also add a CONFIG_PPC_DENORMALISATION option and sets it in
> > pseries/ppc64_defconfig. 
> > 
> > This is useful on bare metal systems only.  Based on patch from Milton
> > Miller.
> > 
> > Signed-off-by: Michael Neuling <[email-masked]>
> > 
> > ---
> > arch/powerpc/Kconfig                   |    7 +
> > arch/powerpc/configs/ppc64_defconfig   |    1 
> > arch/powerpc/configs/pseries_defconfig |    1 
> > arch/powerpc/include/asm/ppc-opcode.h  |    2 
> > arch/powerpc/include/asm/reg.h         |    1 
> > arch/powerpc/kernel/exceptions-64s.S   |  125 +++++++++++++++++++++++++++++++++
> > 6 files changed, 137 insertions(+)
> 
> Is it possible to run POWER6/7 systems in baremetal if you are not IBM?
> 
> Just wondering if this is useful to anyone but IBM.

While I cannot obviously comment on unreleased systems, the fact that
we've been contributing all sort of patches to run P7 in "HV" mode and
KVM on them should be enough of a hint :-)

Cheers,
Ben.