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Subject[PATCH v2 5/6] RISC-V: Move spinwait booting method to its own config
Date
The spinwait booting method should only be used for platforms with older
firmware without SBI HSM extension or M-mode firmware because spinwait
method can't support cpu hotplug, kexec or sparse hartid. It is better
to move the entire spinwait implementation to its own config which can
be disabled if required. It is enabled by default to maintain backward
compatibility and M-mode Linux.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
arch/riscv/Kconfig | 14 ++++++++++++++
arch/riscv/kernel/Makefile | 3 ++-
arch/riscv/kernel/cpu_ops.c | 8 ++++++++
arch/riscv/kernel/head.S | 8 ++++----
arch/riscv/kernel/head.h | 2 ++
5 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 821252b65f89..50c986a446df 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -403,6 +403,20 @@ config RISCV_SBI_V01
This config allows kernel to use SBI v0.1 APIs. This will be
deprecated in future once legacy M-mode software are no longer in use.

+config RISCV_BOOT_SPINWAIT
+ bool "Spinwait booting method"
+ depends on SMP
+ default y
+ help
+ This enables support for booting Linux via spinwait method. In the
+ spinwait method, all cores randomly jump to Linux. One of the cores
+ gets chosen via lottery and all other keep spinning on a percpu
+ variable. This method cannot support CPU hotplug and sparse hartid
+ scheme. It should be only enabled for M-mode Linux or platforms relying
+ on older firmware without SBI HSM extension. All other platforms should
+ rely on ordered booting via SBI HSM extension which gets chosen
+ dynamically at runtime if the firmware supports it.
+
config KEXEC
bool "Kexec system call"
select KEXEC_CORE
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 3397ddac1a30..612556faa527 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -43,7 +43,8 @@ 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_RISCV_BOOT_SPINWAIT) += 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
index c1e30f403c3b..170d07e57721 100644
--- a/arch/riscv/kernel/cpu_ops.c
+++ b/arch/riscv/kernel/cpu_ops.c
@@ -15,7 +15,15 @@
const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;

extern const struct cpu_operations cpu_ops_sbi;
+#ifdef CONFIG_RISCV_BOOT_SPINWAIT
extern const struct cpu_operations cpu_ops_spinwait;
+#else
+const struct cpu_operations cpu_ops_spinwait = {
+ .name = "",
+ .cpu_prepare = NULL,
+ .cpu_start = NULL,
+};
+#endif

void __init cpu_set_ops(int cpuid)
{
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 9f16bfe9307e..db062279d9ed 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -259,7 +259,7 @@ pmp_done:
li t0, SR_FS
csrc CSR_STATUS, t0

-#ifdef CONFIG_SMP
+#ifdef CONFIG_RISCV_BOOT_SPINWAIT
li t0, CONFIG_NR_CPUS
blt a0, t0, .Lgood_cores
tail .Lsecondary_park
@@ -285,7 +285,7 @@ pmp_done:
beq t0, t1, .Lsecondary_start

#endif /* CONFIG_XIP */
-#endif /* CONFIG_SMP */
+#endif /* CONFIG_RISCV_BOOT_SPINWAIT */

#ifdef CONFIG_XIP_KERNEL
la sp, _end + THREAD_SIZE
@@ -344,7 +344,7 @@ clear_bss_done:
call soc_early_init
tail start_kernel

-#ifdef CONFIG_SMP
+#if CONFIG_RISCV_BOOT_SPINWAIT
.Lsecondary_start:
/* Set trap vector to spin forever to help debug */
la a3, .Lsecondary_park
@@ -371,7 +371,7 @@ clear_bss_done:
fence

tail secondary_start_common
-#endif
+#endif /* CONFIG_RISCV_BOOT_SPINWAIT */

END(_start_kernel)

diff --git a/arch/riscv/kernel/head.h b/arch/riscv/kernel/head.h
index 5393cca77790..726731ada534 100644
--- a/arch/riscv/kernel/head.h
+++ b/arch/riscv/kernel/head.h
@@ -16,7 +16,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa);
asmlinkage void __init __copy_data(void);
#endif

+#ifdef CONFIG_RISCV_BOOT_SPINWAIT
extern void *__cpu_spinwait_stack_pointer[];
extern void *__cpu_spinwait_task_pointer[];
+#endif

#endif /* __ASM_HEAD_H */
--
2.33.1
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