powerpc: Add denormalisation exception handling for POWER6/7

On POWER6 and POWER7 if the input operand to an instruction is a
denormalised single precision binary floating point value 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 <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 98e513b62709..748ccaa3b4b3 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -560,6 +560,14 @@ config SCHED_SMT
           when dealing with POWER5 cpus at a cost of slightly increased
           overhead in some places. If unsure say N here.
 
+config PPC_DENORMALISATION
+        bool "PowerPC denormalisation exception handling"
+        depends on PPC_BOOK3S_64
+        default "n"
+        ---help---
+          Add support for handling denormalisation of single precision
+          values.  Useful for bare metal only.  If unsure say Y here.
+
 config CMDLINE_BOOL
         bool "Default bootloader kernel arguments"