powerpc/85xx: Workaroudn e500 CPU erratum A005

This erratum can occur if a single-precision floating-point,
double-precision floating-point or vector floating-point instruction on a
mispredicted branch path signals one of the floating-point data interrupts
which are enabled by the SPEFSCR (FINVE, FDBZE, FUNFE or FOVFE bits).  This
interrupt must be recorded in a one-cycle window when the misprediction is
resolved.  If this extremely rare event should occur, the result could be:

The SPE Data Exception from the mispredicted path may be reported
erroneously if a single-precision floating-point, double-precision
floating-point or vector floating-point instruction is the second
instruction on the correct branch path.

According to errata description, some efp instructions which are not
supposed to trigger SPE exceptions can trigger the exceptions in this case.
However, as we haven't emulated these instructions here, a signal will
send to userspace, and userspace application would exit.

This patch re-issue the efp instruction that we haven't emulated,
so that hardware can properly execute it again if this case happen.

Signed-off-by: Liu Yu <yu.liu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/include/asm/reg.h

@@ -862,6 +862,8 @@
 #define PVR_7450	0x80000000
 #define PVR_8540	0x80200000
 #define PVR_8560	0x80200000
+#define PVR_VER_E500V1	0x8020
+#define PVR_VER_E500V2	0x8021
 /*
  * For the 8xx processors, all of them report the same PVR family for
  * the PowerPC core. The various versions of these processors must be

arch/powerpc/math-emu/math_efp.c

@@ -1,7 +1,7 @@
 /*
  * arch/powerpc/math-emu/math_efp.c
  *
- * Copyright (C) 2006-2008 Freescale Semiconductor, Inc. All rights reserved.
+ * Copyright (C) 2006-2008, 2010 Freescale Semiconductor, Inc.
  *
  * Author: Ebony Zhu,	<ebony.zhu@freescale.com>
  *         Yu Liu,	<yu.liu@freescale.com>
@@ -104,6 +104,8 @@
 #define FP_EX_MASK	(FP_EX_INEXACT | FP_EX_INVALID | FP_EX_DIVZERO | \
 			FP_EX_UNDERFLOW | FP_EX_OVERFLOW)
 
+static int have_e500_cpu_a005_erratum;
+
 union dw_union {
 	u64 dp[1];
 	u32 wp[2];
@@ -652,6 +654,15 @@ int do_spe_mathemu(struct pt_regs *regs)
 	return 0;
 
 illegal:
+	if (have_e500_cpu_a005_erratum) {
+		/* according to e500 cpu a005 erratum, reissue efp inst */
+		regs->nip -= 4;
+#ifdef DEBUG
+		printk(KERN_DEBUG "re-issue efp inst: %08lx\n", speinsn);
+#endif
+		return 0;
+	}
+
 	printk(KERN_ERR "\nOoops! IEEE-754 compliance handler encountered un-supported instruction.\ninst code: %08lx\n", speinsn);
 	return -ENOSYS;
 }
@@ -718,3 +729,43 @@ int speround_handler(struct pt_regs *regs)
 
 	return 0;
 }
+
+int __init spe_mathemu_init(void)
+{
+	u32 pvr, maj, min;
+
+	pvr = mfspr(SPRN_PVR);
+
+	if ((PVR_VER(pvr) == PVR_VER_E500V1) ||
+	    (PVR_VER(pvr) == PVR_VER_E500V2)) {
+		maj = PVR_MAJ(pvr);
+		min = PVR_MIN(pvr);
+
+		/*
+		 * E500 revision below 1.1, 2.3, 3.1, 4.1, 5.1
+		 * need cpu a005 errata workaround
+		 */
+		switch (maj) {
+		case 1:
+			if (min < 1)
+				have_e500_cpu_a005_erratum = 1;
+			break;
+		case 2:
+			if (min < 3)
+				have_e500_cpu_a005_erratum = 1;
+			break;
+		case 3:
+		case 4:
+		case 5:
+			if (min < 1)
+				have_e500_cpu_a005_erratum = 1;
+			break;
+		default:
+			break;
+		}
+	}
+
+	return 0;
+}
+
+module_init(spe_mathemu_init);