MIPS: kernel: mips-r2-to-r6-emul: Add R2 emulator for MIPS R6

MIPS R6 removed quite a few R2 instructions. However, there
is plenty of <R6 userland code so we add an in-kernel emulator
so we can still be able to execute all R2 userland out there.

The emulator comes with a handy debugfs under /mips/ directory
(r2-emul-stats) to provide some basic statistics of the
instructions that are being emulated.

Below are some statistics from booting a minimal buildroot image:

Instruction     Total   BDslot
------------------------------
movs            236969  0
hilo            56686   0
muls            55279   0
divs            10941   0
dsps            0       0
bops            1       0
traps           0       0
fpus            0       0
loads           214981  17
stores          103364  0
llsc            56898   0
dsemul          150418  0
jr              370158
bltzl           43
bgezl           1594
bltzll          0
bgezll          0
bltzal          39
bgezal          39
beql            14503
bnel            138741
blezl           0
bgtzl           3988

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 883eb3aacedf..afa808ab9f44 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -2063,6 +2063,19 @@ config MIPS_MT_FPAFF
         default y
         depends on MIPS_MT_SMP
 
+config MIPSR2_TO_R6_EMULATOR
+        bool "MIPS R2-to-R6 emulator"
+        depends on CPU_MIPSR6 && !SMP
+        default y
+        help
+          Choose this option if you want to run non-R6 MIPS userland code.
+          Even if you say 'Y' here, the emulator will still be disabled by
+          default. You can enable it using the 'mipsr2emul' kernel option.
+          The only reason this is a build-time option is to save ~14K from the
+          final kernel image.
+comment "MIPS R2-to-R6 emulator is only available for UP kernels"
+        depends on SMP && CPU_MIPSR6
+
 config MIPS_VPE_LOADER
         bool "VPE loader support."
         depends on SYS_SUPPORTS_MULTITHREADING && MODULES