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Subject[PATCH v11 07/11] RISC-V: Add cpu_ops and modify default booting method
Date
Currently, all non-booting harts start booting after the booting hart
updates the per-hart stack pointer. This is done in a way that, it's
difficult to implement any other booting method without breaking the
backward compatibility.

Define a cpu_ops method that allows to introduce other booting methods
in future. Modify the current booting method to be compatible with
cpu_ops.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
---
arch/riscv/include/asm/cpu_ops.h | 34 +++++++++++++++++++
arch/riscv/kernel/Makefile | 2 ++
arch/riscv/kernel/cpu_ops.c | 38 +++++++++++++++++++++
arch/riscv/kernel/cpu_ops_spinwait.c | 43 +++++++++++++++++++++++
arch/riscv/kernel/smpboot.c | 51 ++++++++++++++++------------
5 files changed, 147 insertions(+), 21 deletions(-)
create mode 100644 arch/riscv/include/asm/cpu_ops.h
create mode 100644 arch/riscv/kernel/cpu_ops.c
create mode 100644 arch/riscv/kernel/cpu_ops_spinwait.c

diff --git a/arch/riscv/include/asm/cpu_ops.h b/arch/riscv/include/asm/cpu_ops.h
new file mode 100644
index 000000000000..5ce81a28e1d9
--- /dev/null
+++ b/arch/riscv/include/asm/cpu_ops.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2020 Western Digital Corporation or its affiliates.
+ * Based on arch/arm64/include/asm/cpu_ops.h
+ */
+#ifndef __ASM_CPU_OPS_H
+#define __ASM_CPU_OPS_H
+
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/threads.h>
+
+/**
+ * struct cpu_operations - Callback operations for hotplugging CPUs.
+ *
+ * @name: Name of the boot protocol.
+ * @cpu_prepare: Early one-time preparation step for a cpu. If there
+ * is a mechanism for doing so, tests whether it is
+ * possible to boot the given HART.
+ * @cpu_start: Boots a cpu into the kernel.
+ */
+struct cpu_operations {
+ const char *name;
+ int (*cpu_prepare)(unsigned int cpu);
+ int (*cpu_start)(unsigned int cpu,
+ struct task_struct *tidle);
+};
+
+extern const struct cpu_operations *cpu_ops[NR_CPUS];
+void __init cpu_set_ops(int cpu);
+void cpu_update_secondary_bootdata(unsigned int cpuid,
+ struct task_struct *tidle);
+
+#endif /* ifndef __ASM_CPU_OPS_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f40205cb9a22..f81a6ff88005 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -32,6 +32,8 @@ obj-$(CONFIG_RISCV_M_MODE) += clint.o
obj-$(CONFIG_FPU) += fpu.o
obj-$(CONFIG_SMP) += smpboot.o
obj-$(CONFIG_SMP) += smp.o
+obj-$(CONFIG_SMP) += cpu_ops.o
+obj-$(CONFIG_SMP) += cpu_ops_spinwait.o
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_MODULE_SECTIONS) += module-sections.o

diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
new file mode 100644
index 000000000000..62705908eee5
--- /dev/null
+++ b/arch/riscv/kernel/cpu_ops.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/of.h>
+#include <linux/string.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <asm/cpu_ops.h>
+#include <asm/sbi.h>
+#include <asm/smp.h>
+
+const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
+
+void *__cpu_up_stack_pointer[NR_CPUS];
+void *__cpu_up_task_pointer[NR_CPUS];
+
+extern const struct cpu_operations cpu_ops_spinwait;
+
+void cpu_update_secondary_bootdata(unsigned int cpuid,
+ struct task_struct *tidle)
+{
+ int hartid = cpuid_to_hartid_map(cpuid);
+
+ /* Make sure tidle is updated */
+ smp_mb();
+ WRITE_ONCE(__cpu_up_stack_pointer[hartid],
+ task_stack_page(tidle) + THREAD_SIZE);
+ WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
+}
+
+void __init cpu_set_ops(int cpuid)
+{
+ cpu_ops[cpuid] = &cpu_ops_spinwait;
+}
diff --git a/arch/riscv/kernel/cpu_ops_spinwait.c b/arch/riscv/kernel/cpu_ops_spinwait.c
new file mode 100644
index 000000000000..b2c957bb68c1
--- /dev/null
+++ b/arch/riscv/kernel/cpu_ops_spinwait.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/errno.h>
+#include <linux/of.h>
+#include <linux/string.h>
+#include <asm/cpu_ops.h>
+#include <asm/sbi.h>
+#include <asm/smp.h>
+
+const struct cpu_operations cpu_ops_spinwait;
+
+static int spinwait_cpu_prepare(unsigned int cpuid)
+{
+ if (!cpu_ops_spinwait.cpu_start) {
+ pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
+ return -ENODEV;
+ }
+ return 0;
+}
+
+static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
+{
+ /*
+ * In this protocol, all cpus boot on their own accord. _start
+ * selects the first cpu to boot the kernel and causes the remainder
+ * of the cpus to spin in a loop waiting for their stack pointer to be
+ * setup by that main cpu. Writing to bootdata
+ * (i.e __cpu_up_stack_pointer) signals to the spinning cpus that they
+ * can continue the boot process.
+ */
+ cpu_update_secondary_bootdata(cpuid, tidle);
+
+ return 0;
+}
+
+const struct cpu_operations cpu_ops_spinwait = {
+ .name = "spinwait",
+ .cpu_prepare = spinwait_cpu_prepare,
+ .cpu_start = spinwait_cpu_start,
+};
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 8bc01f0ca73b..e89396a2a1af 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -25,6 +25,7 @@
#include <linux/sched/task_stack.h>
#include <linux/sched/mm.h>
#include <asm/clint.h>
+#include <asm/cpu_ops.h>
#include <asm/irq.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
@@ -34,8 +35,6 @@

#include "head.h"

-void *__cpu_up_stack_pointer[NR_CPUS];
-void *__cpu_up_task_pointer[NR_CPUS];
static DECLARE_COMPLETION(cpu_running);

void __init smp_prepare_boot_cpu(void)
@@ -46,6 +45,7 @@ void __init smp_prepare_boot_cpu(void)
void __init smp_prepare_cpus(unsigned int max_cpus)
{
int cpuid;
+ int ret;

/* This covers non-smp usecase mandated by "nosmp" option */
if (max_cpus == 0)
@@ -54,6 +54,11 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
for_each_possible_cpu(cpuid) {
if (cpuid == smp_processor_id())
continue;
+ if (cpu_ops[cpuid]->cpu_prepare) {
+ ret = cpu_ops[cpuid]->cpu_prepare(cpuid);
+ if (ret)
+ continue;
+ }
set_cpu_present(cpuid, true);
}
}
@@ -65,6 +70,8 @@ void __init setup_smp(void)
bool found_boot_cpu = false;
int cpuid = 1;

+ cpu_set_ops(0);
+
for_each_of_cpu_node(dn) {
hart = riscv_of_processor_hartid(dn);
if (hart < 0)
@@ -92,36 +99,38 @@ void __init setup_smp(void)
cpuid, nr_cpu_ids);

for (cpuid = 1; cpuid < nr_cpu_ids; cpuid++) {
- if (cpuid_to_hartid_map(cpuid) != INVALID_HARTID)
+ if (cpuid_to_hartid_map(cpuid) != INVALID_HARTID) {
+ cpu_set_ops(cpuid);
set_cpu_possible(cpuid, true);
+ }
}
}

+int start_secondary_cpu(int cpu, struct task_struct *tidle)
+{
+ if (cpu_ops[cpu]->cpu_start)
+ return cpu_ops[cpu]->cpu_start(cpu, tidle);
+
+ return -EOPNOTSUPP;
+}
+
int __cpu_up(unsigned int cpu, struct task_struct *tidle)
{
int ret = 0;
- int hartid = cpuid_to_hartid_map(cpu);
tidle->thread_info.cpu = cpu;

- /*
- * On RISC-V systems, all harts boot on their own accord. Our _start
- * selects the first hart to boot the kernel and causes the remainder
- * of the harts to spin in a loop waiting for their stack pointer to be
- * setup by that main hart. Writing __cpu_up_stack_pointer signals to
- * the spinning harts that they can continue the boot process.
- */
- smp_mb();
- WRITE_ONCE(__cpu_up_stack_pointer[hartid],
- task_stack_page(tidle) + THREAD_SIZE);
- WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
-
- lockdep_assert_held(&cpu_running);
- wait_for_completion_timeout(&cpu_running,
+ ret = start_secondary_cpu(cpu, tidle);
+ if (!ret) {
+ lockdep_assert_held(&cpu_running);
+ wait_for_completion_timeout(&cpu_running,
msecs_to_jiffies(1000));

- if (!cpu_online(cpu)) {
- pr_crit("CPU%u: failed to come online\n", cpu);
- ret = -EIO;
+ if (!cpu_online(cpu)) {
+ pr_crit("CPU%u: failed to come online\n", cpu);
+ ret = -EIO;
+ }
+ } else {
+ pr_crit("CPU%u: failed to start\n", cpu);
}

return ret;
--
2.25.1
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