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SubjectRe: [PATCH v5] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to sysfs
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On 16/06/16 17:43, Will Deacon wrote:
> On Thu, Jun 16, 2016 at 02:28:50PM +0100, Suzuki K Poulose wrote:
>> +static int __init cpuinfo_regs_init(void)
>> +{
>> + int cpu, finalcpu, ret;
>> + struct device *dev;
>> +
>> + cpu_hotplug_disable();
>> +
>> + for_each_present_cpu(cpu) {
>> + dev = get_cpu_device(cpu);
>> +
>> + if (!dev) {
>> + ret = -ENODEV;
>> + break;
>> + }
>> +
>> + ret = sysfs_create_group(&dev->kobj, &cpuregs_attr_group);
>> + if (ret)
>> + break;
>> + }
>> +
>> + if (!ret)
>> + goto out;
>> + /*
>> + * We were unable to put down sysfs groups for all the CPUs, revert
>> + * all the groups we have placed down s.t. none are visible.
>> + * Otherwise we could give a misleading picture of what's present.
>> + */
>> + finalcpu = cpu;
>> + for_each_present_cpu(cpu) {
>> + if (cpu == finalcpu)
>> + break;
>> + dev = get_cpu_device(cpu);
>> + if (dev)
>> + sysfs_remove_group(&dev->kobj, &cpuregs_attr_group);
>> + }
>> +
>> +out:
>> + cpu_hotplug_enable();
>> + return ret;
>> +}
>> +
>> +device_initcall(cpuinfo_regs_init);
>
> Given that you're built the sysfs entries out of the present mask, don't
> you need a hotplug notifier to keep things up to date?

We already check if the CPU is present at runtime before we give out the data.

+#define CPUINFO_ATTR_RO(_name) \
+ static ssize_t show_##_name (struct device *dev, \
+ struct device_attribute *attr, char *buf) \
+ { \
+ struct cpuinfo_arm64 *info = &per_cpu(cpu_data, dev->id); \
+ if (!cpu_present(dev->id)) \
+ return -ENODEV; \
+ \

Did you mean to check online/offline ?

Cheers
Suzuki

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