[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>

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

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,

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

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)

include/asm-powerpc/cputable.h

@@ -126,6 +126,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTR_NODSISRALIGN		ASM_CONST(0x0000000000100000)
 #define CPU_FTR_PPC_LE			ASM_CONST(0x0000000000200000)
 #define CPU_FTR_REAL_LE			ASM_CONST(0x0000000000400000)
+#define CPU_FTR_FPU_UNAVAILABLE		ASM_CONST(0x0000000000800000)
 
 /*
  * Add the 64-bit processor unique features in the top half of the word;
@@ -295,6 +296,9 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTRS_E300	(CPU_FTR_SPLIT_ID_CACHE | CPU_FTR_MAYBE_CAN_DOZE | \
 	    CPU_FTR_USE_TB | CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_HAS_HIGH_BATS | \
 	    CPU_FTR_COMMON)
+#define CPU_FTRS_E300C2	(CPU_FTR_SPLIT_ID_CACHE | CPU_FTR_MAYBE_CAN_DOZE | \
+	    CPU_FTR_USE_TB | CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_HAS_HIGH_BATS | \
+	    CPU_FTR_COMMON | CPU_FTR_FPU_UNAVAILABLE)
 #define CPU_FTRS_CLASSIC32	(CPU_FTR_COMMON | CPU_FTR_SPLIT_ID_CACHE | \
 	    CPU_FTR_USE_TB | CPU_FTR_HPTE_TABLE)
 #define CPU_FTRS_8XX	(CPU_FTR_SPLIT_ID_CACHE | CPU_FTR_USE_TB)
@@ -364,7 +368,8 @@ enum {
 	    CPU_FTRS_7450_21 | CPU_FTRS_7450_23 | CPU_FTRS_7455_1 |
 	    CPU_FTRS_7455_20 | CPU_FTRS_7455 | CPU_FTRS_7447_10 |
 	    CPU_FTRS_7447 | CPU_FTRS_7447A | CPU_FTRS_82XX |
-	    CPU_FTRS_G2_LE | CPU_FTRS_E300 | CPU_FTRS_CLASSIC32 |
+	    CPU_FTRS_G2_LE | CPU_FTRS_E300 | CPU_FTRS_E300C2 |
+	    CPU_FTRS_CLASSIC32 |
 #else
 	    CPU_FTRS_GENERIC_32 |
 #endif
@@ -403,7 +408,8 @@ enum {
 	    CPU_FTRS_7450_21 & CPU_FTRS_7450_23 & CPU_FTRS_7455_1 &
 	    CPU_FTRS_7455_20 & CPU_FTRS_7455 & CPU_FTRS_7447_10 &
 	    CPU_FTRS_7447 & CPU_FTRS_7447A & CPU_FTRS_82XX &
-	    CPU_FTRS_G2_LE & CPU_FTRS_E300 & CPU_FTRS_CLASSIC32 &
+	    CPU_FTRS_G2_LE & CPU_FTRS_E300 & CPU_FTRS_E300C2 &
+	    CPU_FTRS_CLASSIC32 &
 #else
 	    CPU_FTRS_GENERIC_32 &
 #endif