[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>

4 files changed, 11 insertions, 2 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 291c95ac4b31..0b2d05da89d7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -706,7 +706,7 @@ config FORCE_MAX_ZONEORDER
 
 config MATH_EMULATION
         bool "Math emulation"
-        depends on 4xx || 8xx || E200 || E500
+        depends on 4xx || 8xx || E200 || PPC_83xx || E500
         ---help---
           Some PowerPC chips designed for embedded applications do not have
           a floating-point unit and therefore do not implement the
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 9d1614c3ce67..11bfbaf655b5 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -833,7 +833,7 @@ static struct cpu_spec cpu_specs[] = {
                 .pvr_mask               = 0x7fff0000,
                 .pvr_value              = 0x00840000,
                 .cpu_name               = "e300c2",
-                .cpu_features           = CPU_FTRS_E300,
+                .cpu_features           = CPU_FTRS_E300C2,
                 .cpu_user_features      = PPC_FEATURE_32 | PPC_FEATURE_HAS_MMU,
                 .icache_bsize           = 32,
                 .dcache_bsize           = 32,
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index d88e182e40b3..9417cf5b4b7e 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
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)