• Jordan Niethe's avatar
    powerpc/64s: Set reserved PCR bits · 13c7bb3c
    Jordan Niethe authored
    Currently the reserved bits of the Processor Compatibility
    Register (PCR) are cleared as per the Programming Note in Section
    1.3.3 of version 3.0B of the Power ISA. This causes all new
    architecture features to be made available when running on newer
    processors with new architecture features added to the PCR as bits
    must be set to disable a given feature.
    
    For example to disable new features added as part of Version 2.07 of
    the ISA the corresponding bit in the PCR needs to be set.
    
    As new processor features generally require explicit kernel support
    they should be disabled until such support is implemented. Therefore
    kernels should set all unknown/reserved bits in the PCR such that any
    new architecture features which the kernel does not currently know
    about get disabled.
    
    An update is planned to the ISA to clarify that the PCR is an
    exception to the Programming Note on reserved bits in Section 1.3.3.
    Signed-off-by: default avatarAlistair Popple <alistair@popple.id.au>
    Signed-off-by: default avatarJordan Niethe <jniethe5@gmail.com>
    Tested-by: default avatarJoel Stanley <joel@jms.id.au>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20190917004605.22471-2-alistair@popple.id.au
    13c7bb3c
reg.h 62.9 KB