[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, 7 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index d88e182e40b..9417cf5b4b7 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -437,6 +437,13 @@ Alignment:
 /* Floating-point unavailable */
         . = 0x800
 FPUnavailable:
+BEGIN_FTR_SECTION
+/*
+ * Certain Freescale cores don't have a FPU and treat fp instructions
+ * as a FP Unavailable exception.  Redirect to illegal/emulation handling.
+ */
+        b       ProgramCheck
+END_FTR_SECTION_IFSET(CPU_FTR_FPU_UNAVAILABLE)
         EXCEPTION_PROLOG
         bne     load_up_fpu             /* if from user, just load it up */
         addi    r3,r1,STACK_FRAME_OVERHEAD