Add missing microMIPS support to Malta. Currently the kernel only enables support for the instruction set for the SEAD-3 board despite the fact processor features have nothing to do with the board a processor is installed in. In this case there is no way to run microMIPS software in a fully supported way under Linux on QEMU. QEMU supports the emulation of a Malta board, but does not emulate SEAD-3. Linux supports running microMIPS code on a SEAD-3 board, but hardcodes such support to off on an emulated Malta board even if the processor selected has the microMIPS instruction set implemented. Adding support for the SEAD-3 to QEMU is a major project. Flipping a bit in the kernel that shouldn't have been cleared in the first place is a trivial effort. Thus the answer is plain... Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxxxx> --- Hi, Depending on a processor configuration and particular software run you may get away -- as long as your code doesn't trap into the kernel for emulation. This makes things even more frustrating as the thing appears to run at first and then breaks in an odd place. Frankly I fail to see the point of having microMIPS disabled unless the processor implied by the platform is plain too old (e.g. the DECstation) or otherwise not ever supposed to support it (e.g. NetLogic or Octeon). But I'll leave that for another occasion, for now let's just fix the Malta that has an actual use. Hmm, we should probably have: BUG_ON(!cpu_has_mmips && (cpu_data[0].options & MIPS_CPU_MICROMIPS)); somewhere too, to avoid leading user code astray; we may consider more consistency checks like this for cpu-feature-overrides.h, but this one is at least semi-obvious. Another, less invasive way could be the ELF loader refusing microMIPS executables if (!cpu_has_mmips), but that has the drawback the user won't notice until the last moment. We could have a similar `cpu_has_mips16' override too if people are so concerned with the kernel binary size increase with optional features, and consequently `cpu_has_mips', for pure-microMIPS processors. Please apply. Maciej linux-malta-micromips.diff Index: linux-3.18-rc4-malta/arch/mips/Kconfig =================================================================== --- linux-3.18-rc4-malta.orig/arch/mips/Kconfig 2014-11-15 05:55:54.441908087 +0000 +++ linux-3.18-rc4-malta/arch/mips/Kconfig 2014-11-15 05:55:56.441902868 +0000 @@ -340,6 +340,7 @@ config MIPS_MALTA select SYS_SUPPORTS_64BIT_KERNEL select SYS_SUPPORTS_BIG_ENDIAN select SYS_SUPPORTS_LITTLE_ENDIAN + select SYS_SUPPORTS_MICROMIPS select SYS_SUPPORTS_MIPS_CMP select SYS_SUPPORTS_MIPS_CPS select SYS_SUPPORTS_MIPS16
