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

On 16/06/16 17:43, Will Deacon wrote:

On Thu, Jun 16, 2016 at 02:28:50PM +0100, Suzuki K Poulose wrote:

quoted

+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