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Message-ID: <CAAhSdy26i0KiHce_FveXS795WecSJJ3ujbCmOVVVBiSOd8chRw@mail.gmail.com>
Date: Mon, 13 Dec 2021 18:31:53 +0530
From: Anup Patel <anup@...infault.org>
To: Atish Patra <atishp@...shpatra.org>
Cc: "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
Atish Patra <atishp@...osinc.com>,
Alexandre Ghiti <alex@...ti.fr>,
Anup Patel <anup.patel@....com>,
Greentime Hu <greentime.hu@...ive.com>,
Guo Ren <guoren@...ux.alibaba.com>,
Heinrich Schuchardt <xypron.glpk@....de>,
Ingo Molnar <mingo@...nel.org>,
Jisheng Zhang <jszhang@...nel.org>,
kvm-riscv@...ts.infradead.org, KVM General <kvm@...r.kernel.org>,
linux-riscv <linux-riscv@...ts.infradead.org>,
Marc Zyngier <maz@...nel.org>,
Nanyong Sun <sunnanyong@...wei.com>,
Nick Kossifidis <mick@....forth.gr>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Pekka Enberg <penberg@...nel.org>,
Vincent Chen <vincent.chen@...ive.com>,
Vitaly Wool <vitaly.wool@...sulko.com>
Subject: Re: [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@...shpatra.org> wrote:
>
> From: Atish Patra <atishp@...osinc.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@...osinc.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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