• Suzuki K. Poulose's avatar
    arm64: Delay cpu feature capability checks · dbb4e152
    Suzuki K. Poulose authored
    At the moment we run through the arm64_features capability list for
    each CPU and set the capability if one of the CPU supports it. This
    could be problematic in a heterogeneous system with differing capabilities.
    Delay the CPU feature checks until all the enabled CPUs are up(i.e,
    smp_cpus_done(), so that we can make better decisions based on the
    overall system capability. Once we decide and advertise the capabilities
    the alternatives can be applied. From this state, we cannot roll back
    a feature to disabled based on the values from a new hotplugged CPU,
    due to the runtime patching and other reasons. So, for all new CPUs,
    we need to make sure that they have the established system capabilities.
    Failing which, we bring the CPU down, preventing it from turning online.
    Once the capabilities are decided, any new CPU booting up goes through
    verification to ensure that it has all the enabled capabilities and also
    invokes the respective enable() method on the CPU.
    The CPU errata checks are not delayed and is still executed per-CPU
    to detect the respective capabilities. If we ever come across a non-errata
    capability that needs to be checked on each-CPU, we could introduce them via
    a new capability table(or introduce a flag), which can be processed per CPU.
    The next patch will make the feature checks use the system wide
    safe value of a feature register.
    NOTE: The enable() methods associated with the capability is scheduled
    on all the CPUs (which is the only use case at the moment). If we need
    a different type of 'enable()' which only needs to be run once on any CPU,
    we should be able to handle that when needed.
    Signed-off-by: default avatarSuzuki K. Poulose <suzuki.poulose@arm.com>
    Tested-by: default avatarDave Martin <Dave.Martin@arm.com>
    [catalin.marinas@arm.com: static variable and coding style fixes]
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
cpuinfo.c 6.42 KB