Re: [PATCH v5] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to sysfs

[Suzuki K Poulose]

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