[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, 47 insertions, 13 deletions

diff --git a/arch/mips/lib/memcpy.S b/arch/mips/lib/memcpy.S
index a526c62cb76a..aded7b159052 100644
--- a/arch/mips/lib/memcpy.S
+++ b/arch/mips/lib/memcpy.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
@@ -271,8 +276,10 @@ EXC(	STORE	t0, UNIT(0)(dst),	s_exc_p4u)
 EXC(    STORE   t1, UNIT(1)(dst),       s_exc_p3u)
 EXC(    STORE   t2, UNIT(2)(dst),       s_exc_p2u)
 EXC(    STORE   t3, UNIT(3)(dst),       s_exc_p1u)
+        .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
@@ -284,8 +291,10 @@ EXC(	LOAD	t0, 0(src),		l_exc)
         ADD     src, src, NBYTES
         SUB     len, len, NBYTES
 EXC(    STORE   t0, 0(dst),             s_exc_p1u)
+        .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)
@@ -364,8 +373,10 @@ EXC(	STORE	t1, UNIT(1)(dst),	s_exc_p3u)
 EXC(    STORE   t2, UNIT(2)(dst),       s_exc_p2u)
 EXC(    STORE   t3, UNIT(3)(dst),       s_exc_p1u)
         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
@@ -378,8 +389,10 @@ EXC(	LDREST	t0, REST(0)(src),	l_exc_copy)
         ADD     src, src, NBYTES
         SUB     len, len, NBYTES
 EXC(    STORE   t0, 0(dst),             s_exc_p1u)
+        .set    reorder                         /* DADDI_WAR */
+        ADD     dst, dst, NBYTES
         bne     len, rem, 1b
-         ADD    dst, dst, NBYTES
+        .set    noreorder
 
 copy_bytes_checklen:
         beqz    len, done
@@ -427,8 +440,10 @@ 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
@@ -446,20 +461,33 @@ 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
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
         bnez    src, 1b
          SUB    src, src, 1
+#else
+        .set    push
+        .set    noat
+        li      v1, 1
+        bnez    src, 1b
+         SUB    src, src, v1
+        .set    pop
+#endif
         jr      ra
          nop
 
 
-#define SEXC(n)                         \
-s_exc_p ## n ## u:                      \
-        jr      ra;                     \
-         ADD    len, len, n*NBYTES
+#define SEXC(n)                                                 \
+        .set    reorder;                        /* DADDI_WAR */ \
+s_exc_p ## n ## u:                                              \
+        ADD     len, len, n*NBYTES;                             \
+        jr      ra;                                             \
+        .set    noreorder
 
 SEXC(8)
 SEXC(7)
@@ -471,8 +499,10 @@ SEXC(2)
 SEXC(1)
 
 s_exc_p1:
+        .set    reorder                         /* DADDI_WAR */
+        ADD     len, len, 1
         jr      ra
-         ADD    len, len, 1
+        .set    noreorder
 s_exc:
         jr      ra
          nop
@@ -502,8 +532,10 @@ r_end_bytes:
         SUB     a2, a2, 0x1
         sb      t0, -1(a0)
         SUB     a1, a1, 0x1
+        .set    reorder                         /* DADDI_WAR */
+        SUB     a0, a0, 0x1
         bnez    a2, r_end_bytes
-         SUB    a0, a0, 0x1
+        .set    noreorder
 
 r_out:
         jr      ra
@@ -514,8 +546,10 @@ r_end_bytes_up:
         SUB     a2, a2, 0x1
         sb      t0, (a0)
         ADD     a1, a1, 0x1
+        .set    reorder                         /* DADDI_WAR */
+        ADD     a0, a0, 0x1
         bnez    a2, r_end_bytes_up
-         ADD    a0, a0, 0x1
+        .set    noreorder
 
         jr      ra
          move   a2, zero