[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>

arch/mips/kernel/genex.S

@@ -6,7 +6,7 @@
  * Copyright (C) 1994 - 2000, 2001, 2003 Ralf Baechle
  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
  * Copyright (C) 2001 MIPS Technologies, Inc.
- * Copyright (C) 2002 Maciej W. Rozycki
+ * Copyright (C) 2002, 2007  Maciej W. Rozycki
  */
 #include <linux/init.h>
 
@@ -471,7 +471,13 @@ NESTED(nmi_handler, PT_SIZE, sp)
 	jr	k0
 	 rfe
 #else
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
 	LONG_ADDIU	k0, 4		/* stall on $k0 */
+#else
+	.set	at=v1
+	LONG_ADDIU	k0, 4
+	.set	noat
+#endif
 	MTC0	k0, CP0_EPC
 	/* I hope three instructions between MTC0 and ERET are enough... */
 	ori	k1, _THREAD_MASK

arch/mips/lib/csum_partial.S

@@ -7,6 +7,7 @@
  *
  * Copyright (C) 1998, 1999 Ralf Baechle
  * Copyright (C) 1999 Silicon Graphics, Inc.
+ * Copyright (C) 2007  Maciej W. Rozycki
  */
 #include <linux/errno.h>
 #include <asm/asm.h>
@@ -52,9 +53,12 @@
 #define UNIT(unit)  ((unit)*NBYTES)
 
 #define ADDC(sum,reg)						\
+	.set	push;						\
+	.set	noat;						\
 	ADD	sum, reg;					\
 	sltu	v1, sum, reg;					\
-	ADD	sum, v1
+	ADD	sum, v1;					\
+	.set	pop
 
 #define CSUM_BIGCHUNK1(src, offset, sum, _t0, _t1, _t2, _t3)	\
 	LOAD	_t0, (offset + UNIT(0))(src);			\
@@ -178,8 +182,10 @@ move_128bytes:
 	CSUM_BIGCHUNK(src, 0x40, sum, t0, t1, t3, t4)
 	CSUM_BIGCHUNK(src, 0x60, sum, t0, t1, t3, t4)
 	LONG_SUBU	t8, t8, 0x01
+	.set	reorder				/* DADDI_WAR */
+	PTR_ADDU	src, src, 0x80
 	bnez	t8, move_128bytes
-	 PTR_ADDU	src, src, 0x80
+	.set	noreorder
 
 1:
 	beqz	t2, 1f
@@ -208,8 +214,10 @@ end_words:
 	lw	t0, (src)
 	LONG_SUBU	t8, t8, 0x1
 	ADDC(sum, t0)
+	.set	reorder				/* DADDI_WAR */
+	PTR_ADDU	src, src, 0x4
 	bnez	t8, end_words
-	 PTR_ADDU	src, src, 0x4
+	.set	noreorder
 
 /* unknown src alignment and < 8 bytes to go  */
 small_csumcpy:
@@ -246,6 +254,8 @@ small_csumcpy:
 1:	ADDC(sum, t1)
 
 	/* fold checksum */
+	.set	push
+	.set	noat
 #ifdef USE_DOUBLE
 	dsll32	v1, sum, 0
 	daddu	sum, v1
@@ -266,6 +276,7 @@ small_csumcpy:
 	srl	sum, sum, 8
 	or	sum, v1
 	andi	sum, 0xffff
+	.set	pop
 1:
 	.set	reorder
 	/* Add the passed partial csum.  */
@@ -373,7 +384,11 @@ small_csumcpy:
 
 #define ADDRMASK (NBYTES-1)
 
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
 	.set	noat
+#else
+	.set	at=v1
+#endif
 
 LEAF(__csum_partial_copy_user)
 	PTR_ADDU	AT, src, len	/* See (1) above. */
@@ -441,8 +456,10 @@ EXC(	STORE	t6, UNIT(6)(dst),	s_exc)
 	ADDC(sum, t6)
 EXC(	STORE	t7, UNIT(7)(dst),	s_exc)
 	ADDC(sum, t7)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, 8*NBYTES
 	bgez	len, 1b
-	 ADD	dst, dst, 8*NBYTES
+	.set	noreorder
 	ADD	len, 8*NBYTES		# revert len (see above)
 
 	/*
@@ -471,8 +488,10 @@ EXC(	STORE	t2, UNIT(2)(dst),	s_exc)
 	ADDC(sum, t2)
 EXC(	STORE	t3, UNIT(3)(dst),	s_exc)
 	ADDC(sum, t3)
+	.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
@@ -485,8 +504,10 @@ EXC(	LOAD	t0, 0(src),		l_exc)
 	SUB	len, len, NBYTES
 EXC(	STORE	t0, 0(dst),		s_exc)
 	ADDC(sum, t0)
+	.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)
@@ -572,8 +593,10 @@ EXC(	STORE	t2, UNIT(2)(dst),	s_exc)
 	ADDC(sum, t2)
 EXC(	STORE	t3, UNIT(3)(dst),	s_exc)
 	ADDC(sum, t3)
+	.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
@@ -587,8 +610,10 @@ EXC(	LDREST	t0, REST(0)(src),	l_exc_copy)
 	SUB	len, len, NBYTES
 EXC(	STORE	t0, 0(dst),		s_exc)
 	ADDC(sum, t0)
+	.set	reorder				/* DADDI_WAR */
+	ADD	dst, dst, NBYTES
 	bne	len, rem, 1b
-	 ADD	dst, dst, NBYTES
+	.set	noreorder
 
 copy_bytes_checklen:
 	beqz	len, done
@@ -631,6 +656,8 @@ copy_bytes_done:
 	ADDC(sum, t2)
 done:
 	/* fold checksum */
+	.set	push
+	.set	noat
 #ifdef USE_DOUBLE
 	dsll32	v1, sum, 0
 	daddu	sum, v1
@@ -651,6 +678,7 @@ done:
 	srl	sum, sum, 8
 	or	sum, v1
 	andi	sum, 0xffff
+	.set	pop
 1:
 	.set reorder
 	ADDC(sum, psum)
@@ -678,8 +706,10 @@ EXC(	lbu	t1, 0(src),	l_exc)
 	SLLV	t1, t1, t2
 	addu	t2, SHIFT_INC
 	ADDC(sum, t1)
+	.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
@@ -697,12 +727,22 @@ l_exc:
 	 * Clear len bytes starting at dst.  Can't call __bzero because it
 	 * might modify len.  An inefficient loop for these rare times...
 	 */
+	.set	reorder				/* DADDI_WAR */
+	SUB	src, len, 1
 	beqz	len, done
-	 SUB	src, len, 1
+	.set	noreorder
 1:	sb	zero, 0(dst)
 	ADD	dst, dst, 1
+	.set	push
+	.set	noat
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
 	bnez	src, 1b
 	 SUB	src, src, 1
+#else
+	li	v1, 1
+	bnez	src, 1b
+	 SUB	src, src, v1
+#endif
 	li	v1, -EFAULT
 	b	done
 	 sw	v1, (errptr)
@@ -712,4 +752,5 @@ s_exc:
 	li	v1, -EFAULT
 	jr	ra
 	 sw	v1, (errptr)
+	.set	pop
 	END(__csum_partial_copy_user)

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