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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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