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    SubjectRe: [PATCH 1/1] irqchip/gicv3: iterate over possible CPUs by for_each_possible_cpu()
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    On 09/15/2017 03:20 AM, Marc Zyngier wrote:
    > On Thu, Sep 14 2017 at 1:15:14 pm BST, zijun_hu <zijun_hu@zoho.com> wrote:
    >> From: zijun_hu <zijun_hu@htc.com>
    >>
    >> get_cpu_number() doesn't use existing helper to iterate over possible
    >> CPUs, so error happens in case of discontinuous @cpu_possible_mask
    >> such as 0b11110001.
    >
    > Do you have an example of such a situation? Your patch is definitely an
    > improvement, but I'd like to understand how you get there...
    >
    > Thanks,
    >
    > M.
    >
    a few conditions which maybe result in discontiguous @cpu_possible_mask
    are noticed and considered of by ARM64 init code as indicated by bellow code
    segments:
    in arch/arm64/kernel/smp.c :
    void __init smp_init_cpus(void) {
    ......
    /*
    * We need to set the cpu_logical_map entries before enabling
    * the cpus so that cpu processor description entries (DT cpu nodes
    * and ACPI MADT entries) can be retrieved by matching the cpu hwid
    * with entries in cpu_logical_map while initializing the cpus.
    * If the cpu set-up fails, invalidate the cpu_logical_map entry.
    */
    for (i = 1; i < nr_cpu_ids; i++) {
    if (cpu_logical_map(i) != INVALID_HWID) {
    if (smp_cpu_setup(i))
    cpu_logical_map(i) = INVALID_HWID;
    }
    }
    ......
    }

    /*
    * Initialize cpu operations for a logical cpu and
    * set it in the possible mask on success
    */
    static int __init smp_cpu_setup(int cpu)
    {
    if (cpu_read_ops(cpu))
    return -ENODEV;

    if (cpu_ops[cpu]->cpu_init(cpu))
    return -ENODEV;

    set_cpu_possible(cpu, true);

    return 0;
    }

    i browses GICv3 drivers code and notice that a little weird code segments

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