[MIPS] R4000/R4400 errata workarounds

 This is the gereric part of R4000/R4400 errata workarounds.  They include 
compiler and assembler support as well as some source code modifications 
to address the problems with some combinations of multiply/divide+shift 
instructions as well as the daddi and daddiu instructions.

 Changes included are as follows:

1. New Kconfig options to select workarounds by platforms as necessary.

2. Arch top-level Makefile to pass necessary options to the compiler; also 
   incompatible configurations are detected (-mno-sym32 unsupported as 
   horribly intrusive for little gain).

3. Bug detection updated and shuffled -- the multiply/divide+shift problem 
   is lethal enough that if not worked around it makes the kernel crash in 
   time_init() because of a division by zero; the daddiu erratum might 
   also trigger early potentially, though I have not observed it.  On the 
   other hand the daddi detection code requires the exception subsystem to 
   have been initialised (and is there mainly for information).

4. r4k_daddiu_bug() added so that the existence of the erratum can be 
   queried by code at the run time as necessary; useful for generated code 
   like TLB fault and copy/clear page handlers.

5. __udelay() updated as it uses multiplication in inline assembly.

 Note that -mdaddi requires modified toolchain (which has been maintained 
by myself and available from my site for ~4years now -- versions covered 
are GCC 2.95.4 - 4.1.2 and binutils from 2.13 onwards).  The -mfix-r4000 
and -mfix-r4400 have been standard for a while though.

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

1 files changed, 9 insertions, 3 deletions

diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index a1f8d8b96b03..a49127af33c8 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -141,6 +141,10 @@ cflags-$(CONFIG_CPU_R8000)	+= -march=r8000 -Wa,--trap
 cflags-$(CONFIG_CPU_R10000)     += $(call cc-option,-march=r10000,-march=r8000) \
                         -Wa,--trap
 
+cflags-$(CONFIG_CPU_R4000_WORKAROUNDS)  += $(call cc-option,-mfix-r4000,)
+cflags-$(CONFIG_CPU_R4400_WORKAROUNDS)  += $(call cc-option,-mfix-r4400,)
+cflags-$(CONFIG_CPU_DADDI_WORKAROUNDS)  += $(call cc-option,-mno-daddi,)
+
 ifdef CONFIG_CPU_SB1
 ifdef CONFIG_SB1_PASS_1_WORKAROUNDS
 MODFLAGS        += -msb1-pass1-workarounds
@@ -602,9 +606,11 @@ ifdef CONFIG_64BIT
     endif
   endif
 
-  ifeq ($(KBUILD_SYM32), y)
-    ifeq ($(call cc-option-yn,-msym32), y)
-      cflags-y += -msym32 -DKBUILD_64BIT_SYM32
+  ifeq ($(KBUILD_SYM32)$(call cc-option-yn,-msym32), yy)
+    cflags-y += -msym32 -DKBUILD_64BIT_SYM32
+  else
+    ifeq ($(CONFIG_CPU_DADDI_WORKAROUNDS), y)
+      $(error CONFIG_CPU_DADDI_WORKAROUNDS unsupported without -msym32)
     endif
   endif
 endif