[MIPS] R4000/R4400 daddiu erratum workaround

 This complements the generic R4000/R4400 errata workaround code and adds 
bits for the daddiu problem.  In most places it just modifies handwritten 
assembly code so that the assembler is allowed to use a temporary register 
as daddiu may now be treated as a macro that expands to a sequence of li 
and daddu.  It is the AT register or, where AT is unavailable or used 
explicitly for another purpose, an explicitly-named register is selected, 
using the .set at=<reg> feature added recently to gas.  This feature is 
only used if CONFIG_CPU_DADDI_WORKAROUNDS has been set, so if the 
workaround remains disabled, the required version of binutils stays 
unchanged.

 Similarly, daddiu instructions put in branch delay slots in noreorder 
fragments are now taken out of them and the assembler is allowed to 
reorder them itself as possible (which it does making the whole idea of 
scheduling them into delay slots manually questionable).

 Also in the very few places where such a simple conversion was not 
possible, a handcoded longer sequence is implemented.

 Other than that there are changes to code responsible for building the 
TLB fault and page clear/copy handlers to avoid daddiu as appropriate.  
These are only effective if the erratum is verified to be present at the 
run time.

 Finally there is a trivial update to __delay(), because it uses daddiu in 
a branch delay slot.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 20 insertions, 5 deletions

diff --git a/arch/mips/lib/memcpy-inatomic.S b/arch/mips/lib/memcpy-inatomic.S
index 3a534b2baa0..d1b08f5d686 100644
--- a/arch/mips/lib/memcpy-inatomic.S
+++ b/arch/mips/lib/memcpy-inatomic.S
@@ -9,6 +9,7 @@
  * Copyright (C) 1999, 2000, 01, 2002 Silicon Graphics, Inc.
  * Copyright (C) 2002 Broadcom, Inc.
  *   memcpy/copy_user author: Mark Vandevoorde
+ * Copyright (C) 2007  Maciej W. Rozycki
  *
  * Mnemonic names for arguments to memcpy/__copy_user
  */
@@ -175,7 +176,11 @@
 
 	.text
 	.set	noreorder
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
 	.set	noat
+#else
+	.set	at=v1
+#endif
 
 /*
  * A combined memcpy/__copy_user
@@ -268,8 +273,10 @@ EXC(	LOAD	t3, UNIT(3)(src),	l_exc_copy)
 	STORE	t1, UNIT(1)(dst)
 	STORE	t2, UNIT(2)(dst)
 	STORE	t3, UNIT(3)(dst)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, 4*NBYTES
 	beqz	len, done
-	 ADD	dst, dst, 4*NBYTES
+	.set	noreorder
 less_than_4units:
 	/*
 	 * rem = len % NBYTES
@@ -281,8 +288,10 @@ EXC(	LOAD	t0, 0(src),		l_exc)
 	ADD	src, src, NBYTES
 	SUB	len, len, NBYTES
 	STORE	t0, 0(dst)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, NBYTES
 	bne	rem, len, 1b
-	 ADD	dst, dst, NBYTES
+	.set	noreorder
 
 	/*
 	 * src and dst are aligned, need to copy rem bytes (rem < NBYTES)
@@ -361,8 +370,10 @@ EXC(	LDREST	t3, REST(3)(src),	l_exc_copy)
 	STORE	t2, UNIT(2)(dst)
 	STORE	t3, UNIT(3)(dst)
 	PREF(	1, 9*32(dst) )     	# 1 is PREF_STORE (not streamed)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, 4*NBYTES
 	bne	len, rem, 1b
-	 ADD	dst, dst, 4*NBYTES
+	.set	noreorder
 
 cleanup_src_unaligned:
 	beqz	len, done
@@ -375,8 +386,10 @@ EXC(	LDREST	t0, REST(0)(src),	l_exc_copy)
 	ADD	src, src, NBYTES
 	SUB	len, len, NBYTES
 	STORE	t0, 0(dst)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, NBYTES
 	bne	len, rem, 1b
-	 ADD	dst, dst, NBYTES
+	.set	noreorder
 
 copy_bytes_checklen:
 	beqz	len, done
@@ -424,8 +437,10 @@ l_exc_copy:
 EXC(	lb	t1, 0(src),	l_exc)
 	ADD	src, src, 1
 	sb	t1, 0(dst)	# can't fault -- we're copy_from_user
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, 1
 	bne	src, t0, 1b
-	 ADD	dst, dst, 1
+	.set	noreorder
 l_exc:
 	LOAD	t0, TI_TASK($28)
 	 nop