[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, 16 insertions, 0 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 12bf963..11bc17c 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -91,6 +91,9 @@ config MACH_DECSTATION
 	select BOOT_ELF32
 	select CEVT_R4K
 	select CSRC_R4K
+	select CPU_DADDI_WORKAROUNDS if 64BIT
+	select CPU_R4000_WORKAROUNDS if 64BIT
+	select CPU_R4400_WORKAROUNDS if 64BIT
 	select DMA_NONCOHERENT
 	select NO_IOPORT
 	select IRQ_CPU
@@ -1606,6 +1609,19 @@ config GENERIC_CLOCKEVENTS_BROADCAST
 	bool
 
 #
+# CPU non-features
+#
+config CPU_DADDI_WORKAROUNDS
+	bool
+
+config CPU_R4000_WORKAROUNDS
+	bool
+	select CPU_R4400_WORKAROUNDS
+
+config CPU_R4400_WORKAROUNDS
+	bool
+
+#
 # Use the generic interrupt handling code in kernel/irq/:
 #
 config GENERIC_HARDIRQS