RISC-V: Add cpu_ops and modify default booting method

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>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

diff --git a/arch/riscv/include/asm/cpu_ops.h b/arch/riscv/include/asm/cpu_ops.h
new file mode 100644 (file)
index 0000000..5ce81a2
--- /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 d189bd3..43d49ea 100644 (file)
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -34,6 +34,8 @@ 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 (file)
index 0000000..6270590
--- /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 (file)
index 0000000..b2c957b
--- /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 8bc01f0..e89396a 100644 (file)
--- 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;