• Scott Wood's avatar
    arm64: arch_timer: Work around QorIQ Erratum A-008585 · f6dc1576
    Scott Wood authored
    Erratum A-008585 says that the ARM generic timer counter "has the
    potential to contain an erroneous value for a small number of core
    clock cycles every time the timer value changes".  Accesses to TVAL
    (both read and write) are also affected due to the implicit counter
    read.  Accesses to CVAL are not affected.
    
    The workaround is to reread TVAL and count registers until successive
    reads return the same value.  Writes to TVAL are replaced with an
    equivalent write to CVAL.
    
    The workaround is to reread TVAL and count registers until successive reads
    return the same value, and when writing TVAL to retry until counter
    reads before and after the write return the same value.
    
    The workaround is enabled if the fsl,erratum-a008585 property is found in
    the timer node in the device tree.  This can be overridden with the
    clocksource.arm_arch_timer.fsl-a008585 boot parameter, which allows KVM
    users to enable the workaround until a mechanism is implemented to
    automatically communicate this information.
    
    This erratum can be found on LS1043A and LS2080A.
    Acked-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Signed-off-by: default avatarScott Wood <oss@buserror.net>
    [will: renamed read macro to reflect that it's not usually unstable]
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    f6dc1576
arch_timer.h 3.72 KB