• Paul Burton's avatar
    MIPS: Basic MSA context switching support · 1db1af84
    Paul Burton authored
    This patch adds support for context switching the MSA vector registers.
    These 128 bit vector registers are aliased with the FP registers - an
    FP register accesses the least significant bits of the vector register
    with which it is aliased (ie. the register with the same index). Due to
    both this & the requirement that the scalar FPU must be 64-bit (FR=1) if
    enabled at the same time as MSA the kernel will enable MSA & scalar FP
    at the same time for tasks which use MSA. If we restore the MSA vector
    context then we might as well enable the scalar FPU since the reason it
    was left disabled was to allow for lazy FP context restoring - but we
    just restored the FP context as it's a subset of the vector context. If
    we restore the FP context and have previously used MSA then we have to
    restore the whole vector context anyway (see comment in
    enable_restore_fp_context for details) so similarly we might as well
    enable MSA.
    
    Thus if a task does not use MSA then it will continue to behave as
    without this patch - the scalar FP context will be saved & restored as
    usual. But if a task executes an MSA instruction then it will save &
    restore the vector context forever more.
    Signed-off-by: default avatarPaul Burton <paul.burton@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Patchwork: https://patchwork.linux-mips.org/patch/6431/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    1db1af84
process.c 13.9 KB