[POWERPC] Add support for FP emulation for the e300c2 core

The e300c2 has no FPU.  Its MSR[FP] is grounded to zero.  If an attempt
is made to execute a floating point instruction (including floating-point
load, store, or move instructions), the e300c2 takes a floating-point
unavailable interrupt.

This patch adds support for FP emulation on the e300c2 by declaring a
new CPU_FTR_FP_TAKES_FPUNAVAIL, where FP unavail interrupts are
intercepted and redirected to the ProgramCheck exception path for
correct emulation handling.

(If we run out of CPU_FTR bits we could look to reclaim this bit by adding
support to test the cpu_user_features for PPC_FEATURE_HAS_FPU instead)

It adds a nop to the exception path for 32-bit processors with a FPU.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 0d4e203fa7a0..fde820e52d03 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -782,6 +782,8 @@ void __kprobes program_check_exception(struct pt_regs *regs)
         unsigned int reason = get_reason(regs);
         extern int do_mathemu(struct pt_regs *regs);
 
+        /* We can now get here via a FP Unavailable exception if the core
+         * has no FPU, in that case no reason flags will be set */
 #ifdef CONFIG_MATH_EMULATION
         /* (reason & REASON_ILLEGAL) would be the obvious thing here,
          * but there seems to be a hardware bug on the 405GP (RevD)