[PATCH] e500: Erratum cpu a005 workaround

[Liu Yu]

This errata 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 at freescale.com>
---
This is an erratum workaround patch.
It would be better if the patch can go into 2.6.38.

 arch/powerpc/include/asm/reg.h   |    2 +
 arch/powerpc/math-emu/math_efp.c |   53 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 54 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 6315edc..0abfd91 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -833,6 +833,8 @@
 #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
diff --git a/arch/powerpc/math-emu/math_efp.c b/arch/powerpc/math-emu/math_efp.c
index 41f4ef3..634830b 100644
--- a/arch/powerpc/math-emu/math_efp.c
+++ b/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 at freescale.com>
  *         Yu Liu,	<yu.liu at 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 @@ update_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);
-- 
1.6.4