• Paul Burton's avatar
    MIPS: Simplify FP context initialization · cc97ab23
    Paul Burton authored
    MIPS has up until now had 3 different ways for a task's floating point
    context to be initialized:
    
      - If the task's first use of FP involves it gaining ownership of an
        FPU then _init_fpu() is used to initialize the FPU's registers such
        that they all contain ~0, and the FPU registers will be stored to
        struct thread_info later (eg. when context switching).
    
      - If the task first uses FP on a CPU without an associated FPU then
        fpu_emulator_init_fpu() initializes the task's floating point
        register state in struct thread_info such that all floating point
        register contain the bit pattern 0x7ff800007ff80000, different to
        the _init_fpu() behaviour.
    
      - If a task's floating point context is first accessed via ptrace then
        init_fp_ctx() initializes the floating point register state in
        struct thread_info to ~0, giving equivalent state to _init_fpu().
    
    The _init_fpu() path has 2 separate implementations - one for r2k/r3k
    style systems & one for r4k style systems. The _init_fpu() path also
    requires that we be careful to clear & restore the value of the
    Config5.FRE bit on modern systems in order to avoid inadvertently
    triggering floating point exceptions.
    
    None of this code is in a performance critical hot path - it runs only
    the first time a task uses floating point. As such it doesn't seem to
    warrant the complications of maintaining the _init_fpu() path.
    
    Remove _init_fpu() & fpu_emulator_init_fpu(), instead using
    init_fp_ctx() consistently to initialize floating point register state
    in struct thread_info. Upon a task's first use of floating point this
    will typically mean that we initialize state in memory & then load it
    into FPU registers using _restore_fp() just as we would on a context
    switch. For other paths such as __compute_return_epc_for_insn() or
    mipsr2_decoder() this results in a significant simplification of the
    work to be done.
    Signed-off-by: default avatarPaul Burton <paul.burton@mips.com>
    Patchwork: https://patchwork.linux-mips.org/patch/21002/
    Cc: linux-mips@linux-mips.org
    cc97ab23
r2300_fpu.S 2.84 KB