From f1e58583b9c7ceae7f11646e9edf2561d67f29c9 Mon Sep 17 00:00:00 2001
From: Atish Patra <atish.patra@wdc.com>
Date: Tue, 17 Mar 2020 18:11:44 -0700
Subject: RISC-V: Support cpu hotplug

This patch enable support for cpu hotplug in RISC-V. It uses SBI HSM
extension to online/offline any hart. As a result, the harts are
returned to firmware once they are offline. If the harts are brought
online afterwards, they re-enter Linux kernel as if a secondary hart
booted for the first time. All booting requirements are honored during
this process.

Tested both on QEMU and HighFive Unleashed board with. Test result follows.

---------------------------------------------------
Offline cpu 2
---------------------------------------------------
$ echo 0 > /sys/devices/system/cpu/cpu2/online
[   32.828684] CPU2: off
$ cat /proc/cpuinfo
processor       : 0
hart            : 0
isa             : rv64imafdcsu
mmu             : sv48

processor       : 1
hart            : 1
isa             : rv64imafdcsu
mmu             : sv48

processor       : 3
hart            : 3
isa             : rv64imafdcsu
mmu             : sv48

processor       : 4
hart            : 4
isa             : rv64imafdcsu
mmu             : sv48

processor       : 5
hart            : 5
isa             : rv64imafdcsu
mmu             : sv48

processor       : 6
hart            : 6
isa             : rv64imafdcsu
mmu             : sv48

processor       : 7
hart            : 7
isa             : rv64imafdcsu
mmu             : sv48

---------------------------------------------------
online cpu 2
---------------------------------------------------
$ echo 1 > /sys/devices/system/cpu/cpu2/online
$ cat /proc/cpuinfo
processor       : 0
hart            : 0
isa             : rv64imafdcsu
mmu             : sv48

processor       : 1
hart            : 1
isa             : rv64imafdcsu
mmu             : sv48

processor       : 2
hart            : 2
isa             : rv64imafdcsu
mmu             : sv48

processor       : 3
hart            : 3
isa             : rv64imafdcsu
mmu             : sv48

processor       : 4
hart            : 4
isa             : rv64imafdcsu
mmu             : sv48

processor       : 5
hart            : 5
isa             : rv64imafdcsu
mmu             : sv48

processor       : 6
hart            : 6
isa             : rv64imafdcsu
mmu             : sv48

processor       : 7
hart            : 7
isa             : rv64imafdcsu
mmu             : sv48

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
---
 arch/riscv/kernel/setup.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

(limited to 'arch/riscv/kernel/setup.c')

diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 07f4e7503223..145128a7e560 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -16,12 +16,13 @@
 #include <linux/of_platform.h>
 #include <linux/sched/task.h>
 #include <linux/swiotlb.h>
+#include <linux/smp.h>
 
 #include <asm/clint.h>
+#include <asm/cpu_ops.h>
 #include <asm/setup.h>
 #include <asm/sections.h>
 #include <asm/pgtable.h>
-#include <asm/smp.h>
 #include <asm/sbi.h>
 #include <asm/tlbflush.h>
 #include <asm/thread_info.h>
@@ -47,6 +48,7 @@ struct screen_info screen_info = {
  */
 atomic_t hart_lottery __section(.sdata);
 unsigned long boot_cpu_hartid;
+static DEFINE_PER_CPU(struct cpu, cpu_devices);
 
 void __init parse_dtb(void)
 {
@@ -94,3 +96,18 @@ void __init setup_arch(char **cmdline_p)
 
 	riscv_fill_hwcap();
 }
+
+static int __init topology_init(void)
+{
+	int i;
+
+	for_each_possible_cpu(i) {
+		struct cpu *cpu = &per_cpu(cpu_devices, i);
+
+		cpu->hotpluggable = cpu_has_hotplug(i);
+		register_cpu(cpu, i);
+	}
+
+	return 0;
+}
+subsys_initcall(topology_init);
-- 
cgit