powerpc/pseries: Export raw per-CPU VPA data via debugfs

This patch exports the raw per-CPU VPA data via debugfs.
A per-CPU file is created which exports the VPA data of
that CPU to help debug some of the VPA related issues or
to analyze the per-CPU VPA related statistics.

v3: Removed offline CPU check.

v2: Included offline CPU check and other review comments.
Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/lpar.c

@@ -48,6 +48,7 @@
 #include <asm/kexec.h>
 #include <asm/fadump.h>
 #include <asm/asm-prototypes.h>
+#include <asm/debugfs.h>
 
 #include "pseries.h"
 
@@ -1239,3 +1240,56 @@ static int __init reserve_vrma_context_id(void)
 	return 0;
 }
 machine_device_initcall(pseries, reserve_vrma_context_id);
+
+#ifdef CONFIG_DEBUG_FS
+/* debugfs file interface for vpa data */
+static ssize_t vpa_file_read(struct file *filp, char __user *buf, size_t len,
+			      loff_t *pos)
+{
+	int cpu = (long)filp->private_data;
+	struct lppaca *lppaca = &lppaca_of(cpu);
+
+	return simple_read_from_buffer(buf, len, pos, lppaca,
+				sizeof(struct lppaca));
+}
+
+static const struct file_operations vpa_fops = {
+	.open		= simple_open,
+	.read		= vpa_file_read,
+	.llseek		= default_llseek,
+};
+
+static int __init vpa_debugfs_init(void)
+{
+	char name[16];
+	long i;
+	static struct dentry *vpa_dir;
+
+	if (!firmware_has_feature(FW_FEATURE_SPLPAR))
+		return 0;
+
+	vpa_dir = debugfs_create_dir("vpa", powerpc_debugfs_root);
+	if (!vpa_dir) {
+		pr_warn("%s: can't create vpa root dir\n", __func__);
+		return -ENOMEM;
+	}
+
+	/* set up the per-cpu vpa file*/
+	for_each_possible_cpu(i) {
+		struct dentry *d;
+
+		sprintf(name, "cpu-%ld", i);
+
+		d = debugfs_create_file(name, 0400, vpa_dir, (void *)i,
+					&vpa_fops);
+		if (!d) {
+			pr_warn("%s: can't create per-cpu vpa file\n",
+					__func__);
+			return -ENOMEM;
+		}
+	}
+
+	return 0;
+}
+machine_arch_initcall(pseries, vpa_debugfs_init);
+#endif /* CONFIG_DEBUG_FS */