• Serge Semin's avatar
    mips: Add MIPS Release 5 support · ab7c01fd
    Serge Semin authored
    There are five MIPS32/64 architecture releases currently available:
    from 1 to 6 except fourth one, which was intentionally skipped.
    Three of them can be called as major: 1st, 2nd and 6th, that not only
    have some system level alterations, but also introduced significant
    core/ISA level updates. The rest of the MIPS architecture releases are
    minor.
    
    Even though they don't have as much ISA/system/core level changes
    as the major ones with respect to the previous releases, they still
    provide a set of updates (I'd say they were intended to be the
    intermediate releases before a major one) that might be useful for the
    kernel and user-level code, when activated by the kernel or compiler.
    In particular the following features were introduced or ended up being
    available at/after MIPS32/64 Release 5 architecture:
    + the last release of the misaligned memory access instructions,
    + virtualisation - VZ ASE - is optional component of the arch,
    + SIMD - MSA ASE - is optional component of the arch,
    + DSP ASE is optional component of the arch,
    + CP0.Status.FR=1 for CP1.FIR.F64=1 (pure 64-bit FPU general registers)
      must be available if FPU is implemented,
    + CP1.FIR.Has2008 support is required so CP1.FCSR.{ABS2008,NAN2008} bits
      are available.
    + UFR/UNFR aliases to access CP0.Status.FR from user-space by means of
      ctc1/cfc1 instructions (enabled by CP0.Config5.UFR),
    + CP0.COnfig5.LLB=1 and eretnc instruction are implemented to without
      accidentally clearing LL-bit when returning from an interrupt,
      exception, or error trap,
    + XPA feature together with extended versions of CPx registers is
      introduced, which needs to have mfhc0/mthc0 instructions available.
    
    So due to these changes GNU GCC provides an extended instructions set
    support for MIPS32/64 Release 5 by default like eretnc/mfhc0/mthc0. Even
    though the architecture alteration isn't that big, it still worth to be
    taken into account by the kernel software. Finally we can't deny that
    some optimization/limitations might be found in future and implemented
    on some level in kernel or compiler. In this case having even
    intermediate MIPS architecture releases support would be more than
    useful.
    
    So the most of the changes provided by this commit can be split into
    either compile- or runtime configs related. The compile-time related
    changes are caused by adding the new CONFIG_CPU_MIPS32_R5/CONFIG_CPU_MIPSR5
    configs and concern the code activating MIPSR2 or MIPSR6 already
    implemented features (like eretnc/LLbit, mthc0/mfhc0). In addition
    CPU_HAS_MSA can be now freely enabled for MIPS32/64 release 5 based
    platforms as this is done for CPU_MIPS32_R6 CPUs. The runtime changes
    concerns the features which are handled with respect to the MIPS ISA
    revision detected at run-time by means of CP0.Config.{AT,AR} bits. Alas
    these fields can be used to detect either r1 or r2 or r6 releases.
    But since we know which CPUs in fact support the R5 arch, we can manually
    set MIPS_CPU_ISA_M32R5/MIPS_CPU_ISA_M64R5 bit of c->isa_level and then
    use cpu_has_mips32r5/cpu_has_mips64r5 where it's appropriate.
    
    Since XPA/EVA provide too complex alterationss and to have them used with
    MIPS32 Release 2 charged kernels (for compatibility with current platform
    configs) they are left to be setup as a separate kernel configs.
    Co-developed-by: default avatarAlexey Malahov <Alexey.Malahov@baikalelectronics.ru>
    Signed-off-by: default avatarAlexey Malahov <Alexey.Malahov@baikalelectronics.ru>
    Signed-off-by: default avatarSerge Semin <Sergey.Semin@baikalelectronics.ru>
    Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
    Cc: Paul Burton <paulburton@kernel.org>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Rob Herring <robh+dt@kernel.org>
    Cc: devicetree@vger.kernel.org
    Signed-off-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
    ab7c01fd
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