[PATCH v7 09/10] RISC-V: Add supported for ordered booting method using HSM

[Atish Patra]

Currently, all harts have to jump Linux in RISC-V. This complicates the
multi-stage boot process as every transient stage also has to ensure all
harts enter to that stage and jump to Linux afterwards. It also obstructs
a clean Kexec implementation.

SBI HSM extension provides alternate solutions where only a single hart
need to boot and enter Linux. The booting hart can bring up secondary
harts one by one afterwards.

Add SBI HSM based cpu_ops that implements an ordered booting method in
RISC-V. This change is also backward compatible with older firmware not
implementing HSM extension. If a latest kernel is used with older
firmware, it will continue to use the default spinning booting method.

Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
---
 arch/riscv/kernel/cpu_ops.c | 41 ++++++++++++++++++++++++++++++++++++-
 arch/riscv/kernel/head.S    | 25 ++++++++++++++++++++++
 arch/riscv/kernel/smpboot.c |  2 +-
 arch/riscv/kernel/traps.c   |  2 +-
 4 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
index 099dbb6ff9f0..454df032066f 100644
--- a/arch/riscv/kernel/cpu_ops.c
+++ b/arch/riscv/kernel/cpu_ops.c
@@ -17,9 +17,13 @@ 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 char secondary_start_sbi[];
 
+const struct cpu_operations cpu_sbi_ops;
 const struct cpu_operations cpu_spinwait_ops;
 
+#define RISCV_HART_FIRMWARE_STOPPED 0
+
 static int spinwait_cpu_prepare(unsigned int cpuid)
 {
 	if (!cpu_spinwait_ops.cpu_start) {
@@ -29,6 +33,32 @@ static int spinwait_cpu_prepare(unsigned int cpuid)
 	return 0;
 }
 
+static int sbi_cpu_prepare(unsigned int cpuid)
+{
+	if (!cpu_sbi_ops.cpu_start) {
+		pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
+		return -ENODEV;
+	}
+	return 0;
+}
+
+static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
+{
+	int rc;
+	int hartid = cpuid_to_hartid_map(cpuid);
+	unsigned long boot_addr = __pa_symbol(secondary_start_sbi);
+
+	/* 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);
+
+	rc = sbi_hsm_hart_start(hartid, boot_addr, 0);
+
+	return rc;
+}
+
 static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
 {
 	int hartid = cpuid_to_hartid_map(cpuid);
@@ -48,6 +78,12 @@ static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
 	return 0;
 }
 
+const struct cpu_operations cpu_sbi_ops = {
+	.name		= "sbi",
+	.cpu_prepare	= sbi_cpu_prepare,
+	.cpu_start	= sbi_cpu_start,
+};
+
 const struct cpu_operations cpu_spinwait_ops = {
 	.name		= "spinwait",
 	.cpu_prepare	= spinwait_cpu_prepare,
@@ -56,6 +92,9 @@ const struct cpu_operations cpu_spinwait_ops = {
 
 int __init cpu_set_ops(int cpuid)
 {
-	cpu_ops[cpuid] = &cpu_spinwait_ops;
+	if (sbi_hsm_is_available())
+		cpu_ops[cpuid] = &cpu_sbi_ops;
+	else
+		cpu_ops[cpuid] = &cpu_spinwait_ops;
 	return 0;
 }
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 9d7f084a50cc..3c93973667c8 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -210,11 +210,36 @@ relocate:
 	ret
 #endif /* CONFIG_MMU */
 #ifdef CONFIG_SMP
+	.global secondary_start_sbi
+secondary_start_sbi:
+	/* Mask all interrupts */
+	csrw CSR_IE, zero
+	csrw CSR_IP, zero
+
+	/* Load the global pointer */
+	.option push
+	.option norelax
+		la gp, __global_pointer$
+	.option pop
+
+	/*
+	 * Disable FPU to detect illegal usage of
+	 * floating point in kernel space
+	 */
+	li t0, SR_FS
+	csrc CSR_STATUS, t0
+
 	/* Set trap vector to spin forever to help debug */
 	la a3, .Lsecondary_park
 	csrw CSR_TVEC, a3
 
 	slli a3, a0, LGREG
+	la a4, __cpu_up_stack_pointer
+	la a5, __cpu_up_task_pointer
+	add a4, a3, a4
+	add a5, a3, a5
+	REG_L sp, (a4)
+	REG_L tp, (a5)
 	.global secondary_start_common
 secondary_start_common:
 
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index f2cf541bc895..8ac9115001b9 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -144,7 +144,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
 /*
  * C entry point for a secondary processor.
  */
-asmlinkage __visible void __init smp_callin(void)
+asmlinkage __visible void smp_callin(void)
 {
 	struct mm_struct *mm = &init_mm;
 
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f4cad5163bf2..0063dd7318d6 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -147,7 +147,7 @@ int is_valid_bugaddr(unsigned long pc)
 }
 #endif /* CONFIG_GENERIC_BUG */
 
-void __init trap_init(void)
+void trap_init(void)
 {
 	/*
 	 * Set sup0 scratch register to 0, indicating to exception vector
-- 
2.24.0