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    SubjectRe: [RFC 5/6] RISC-V: Move spinwait booting method to its own config
    On Sat, Dec 4, 2021 at 5:51 AM Atish Patra <atishp@atishpatra.org> wrote:
    >
    > From: Atish Patra <atishp@rivosinc.com>
    >
    > 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 | 6 +++---
    > arch/riscv/kernel/head.h | 2 ++
    > 5 files changed, 29 insertions(+), 4 deletions(-)
    >
    > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
    > index 821252b65f89..4afb42d5707d 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 core
    > + gets chosen via lottery and all other keeps spinning on a percpu
    > + variable. This method can not 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 platform should
    > + rely on ordered booing 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..4a694e15b95b 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 defined(CONFIG_SMP) && defined(CONFIG_RISCV_BOOT_SPINWAIT)

    The RISCV_BOOT_SPINWAIT option already depends on SMP.

    Do you still need to check defined(CONFIG_SMP) here ?

    Regards,
    Anup

    > .Lsecondary_start:
    > /* Set trap vector to spin forever to help debug */
    > la a3, .Lsecondary_park
    > 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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