Re: [PATCH v10 1/8] RISC-V: Enable CPU_IDLE drivers

[Anup Patel]

On Tue, Feb 8, 2022 at 11:46 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
>
> Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>
>
> small questions:
>
> On Wed, Jan 26, 2022 at 7:46 PM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
> >
> > From: Anup Patel <anup.patel@xxxxxxx>
> >
> > We force select CPU_PM and provide asm/cpuidle.h so that we can
> > use CPU IDLE drivers for Linux RISC-V kernel.
> >
> > Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxx>
> > ---
> >  arch/riscv/Kconfig                |  7 +++++++
> >  arch/riscv/configs/defconfig      |  1 +
> >  arch/riscv/configs/rv32_defconfig |  1 +
> >  arch/riscv/include/asm/cpuidle.h  | 24 ++++++++++++++++++++++++
> >  arch/riscv/kernel/process.c       |  3 ++-
> >  5 files changed, 35 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/include/asm/cpuidle.h
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 5adcbd9b5e88..76976d12b463 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -46,6 +46,7 @@ config RISCV
> >         select CLONE_BACKWARDS
> >         select CLINT_TIMER if !MMU
> >         select COMMON_CLK
> > +       select CPU_PM if CPU_IDLE
> >         select EDAC_SUPPORT
> >         select GENERIC_ARCH_TOPOLOGY if SMP
> >         select GENERIC_ATOMIC64 if !64BIT
> > @@ -547,4 +548,10 @@ source "kernel/power/Kconfig"
> >
> >  endmenu
> >
> > +menu "CPU Power Management"
> > +
> > +source "drivers/cpuidle/Kconfig"
> > +
> > +endmenu
> > +
> >  source "arch/riscv/kvm/Kconfig"
> > diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
> > index f120fcc43d0a..a5e0482a4969 100644
> > --- a/arch/riscv/configs/defconfig
> > +++ b/arch/riscv/configs/defconfig
> > @@ -20,6 +20,7 @@ CONFIG_SOC_SIFIVE=y
> >  CONFIG_SOC_VIRT=y
> >  CONFIG_SMP=y
> >  CONFIG_HOTPLUG_CPU=y
> > +CONFIG_CPU_IDLE=y
> >  CONFIG_VIRTUALIZATION=y
> >  CONFIG_KVM=m
> >  CONFIG_JUMP_LABEL=y
> > diff --git a/arch/riscv/configs/rv32_defconfig b/arch/riscv/configs/rv32_defconfig
> > index 8b56a7f1eb06..d1b87db54d68 100644
> > --- a/arch/riscv/configs/rv32_defconfig
> > +++ b/arch/riscv/configs/rv32_defconfig
> > @@ -20,6 +20,7 @@ CONFIG_SOC_VIRT=y
> >  CONFIG_ARCH_RV32I=y
> >  CONFIG_SMP=y
> >  CONFIG_HOTPLUG_CPU=y
> > +CONFIG_CPU_IDLE=y
> >  CONFIG_VIRTUALIZATION=y
> >  CONFIG_KVM=m
> >  CONFIG_JUMP_LABEL=y
> > diff --git a/arch/riscv/include/asm/cpuidle.h b/arch/riscv/include/asm/cpuidle.h
> > new file mode 100644
> > index 000000000000..71fdc607d4bc
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/cpuidle.h
> > @@ -0,0 +1,24 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2021 Allwinner Ltd
> > + * Copyright (C) 2021 Western Digital Corporation or its affiliates.
> > + */
> > +
> > +#ifndef _ASM_RISCV_CPUIDLE_H
> > +#define _ASM_RISCV_CPUIDLE_H
> > +
> > +#include <asm/barrier.h>
> > +#include <asm/processor.h>
> > +
> > +static inline void cpu_do_idle(void)
> > +{
> > +       /*
> > +        * Add mb() here to ensure that all
> > +        * IO/MEM accesses are completed prior
> > +        * to entering WFI.
> > +        */
> > +       mb();
> I think it's a separate fixup.
>
> > +       wait_for_interrupt();
> > +}
> > +
> > +#endif
> > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> > index 03ac3aa611f5..504b496787aa 100644
> > --- a/arch/riscv/kernel/process.c
> > +++ b/arch/riscv/kernel/process.c
> > @@ -23,6 +23,7 @@
> >  #include <asm/string.h>
> >  #include <asm/switch_to.h>
> >  #include <asm/thread_info.h>
> > +#include <asm/cpuidle.h>
> >
> >  register unsigned long gp_in_global __asm__("gp");
> >
> > @@ -37,7 +38,7 @@ extern asmlinkage void ret_from_kernel_thread(void);
> >
> >  void arch_cpu_idle(void)
> >  {
> maybe below is enough.
> + mb();

We can't add "mb()" here because cpu_do_idle() is called
directly from linux/cpuidle.h and arch_cpu_idle() is only
called when CPU idle is disabled.

Regards,
Anup

>    wait_for_interrupt();
>
> > -       wait_for_interrupt();
> > +       cpu_do_idle();
>
>
> >         raw_local_irq_enable();
> >  }
> >
> > --
> > 2.25.1
> >
> >
> > --
> > kvm-riscv mailing list
> > kvm-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/kvm-riscv
>
>
>
> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/