Re: [PATCH] MIPS: Expose prid and globalnumber to sysfs

Some application would like to know precise model and rev of processor
to do errata workaround or optimization.

Expose them in sysfs as:
/sys/devices/system/cpu/cpuX/regs/identification/prid
/sys/devices/system/cpu/cpuX/regs/identification/globalnumber

Reusing AArch64 CPU registers directory.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 .../ABI/testing/sysfs-devices-system-cpu      | 11 +++
 arch/mips/kernel/topology.c                   | 96 +++++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 5bf61881f012..adf855e7bb9b 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu

@@ -512,6 +512,17 @@ Description:	information about CPUs heterogeneity.
 
 		cpu_capacity: capacity of cpuX.
 
+What:		/sys/devices/system/cpu/cpuX/regs/
+		/sys/devices/system/cpu/cpuX/regs/identification/
+		/sys/devices/system/cpu/cpuX/regs/identification/prid
+		/sys/devices/system/cpu/cpuX/regs/identification/globalnumber
+Date:		Augest 2022
+Contact:	Linux MIPS Kernel Mailing list <linux-mips@vger.kernel.org>
+Description:	MIPS CPU registers
+
+		'identification' directory exposes the Processor ID and Global Number
+		registers for identifying model and revision of the CPU.
+
 What:		/sys/devices/system/cpu/vulnerabilities
 		/sys/devices/system/cpu/vulnerabilities/meltdown
 		/sys/devices/system/cpu/vulnerabilities/spectre_v1

diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
index 9429d85a4703..90b5136afb63 100644
--- a/arch/mips/kernel/topology.c
+++ b/arch/mips/kernel/topology.c

@@ -5,6 +5,8 @@
 #include <linux/node.h>
 #include <linux/nodemask.h>
 #include <linux/percpu.h>
+#include <linux/seq_file.h>
+#include <linux/smp.h>
 
 static DEFINE_PER_CPU(struct cpu, cpu_devices);
 

@@ -26,3 +28,97 @@ static int __init topology_init(void)
 }
 
 subsys_initcall(topology_init);
+
+static struct kobj_type cpuregs_kobj_type = {
+	.sysfs_ops = &kobj_sysfs_ops,
+};
+
+struct cpureg {
+	struct kobject kobj;
+	struct cpuinfo_mips *info;
+};
+static DEFINE_PER_CPU(struct cpureg, cpuregs);