Re: [PATCH v3] RISC-V: Use SBI SRST extension when available

[Alistair Francis <Alistair.Francis@wdc.com>]

On Wed, 2020-11-25 at 10:47 +0530, Anup Patel wrote:
> The SBI SRST extension provides a standard way to poweroff and
> reboot the system irrespective to whether Linux RISC-V S-mode
> is running natively (HS-mode) or inside Guest/VM (VS-mode).
> 
> The SBI SRST extension is available in latest SBI v0.3-draft
> specification at: https://github.com/riscv/riscv-sbi-doc.
> 
> This patch extends Linux RISC-V SBI implementation to detect
> and use SBI SRST extension.
> 
> Signed-off-by: Anup Patel <anup.patel@wdc.com>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
> Changes since v2:
>  - Rebased on Linux-5.10-rc5
>  - Updated patch as-per SBI SRST extension available in the latest
>    SBI v0.3-draft specification
> Changes since v1:
>  - Updated patch as-per latest SBI SRST extension draft spec where
>    we have only one SBI call with "reset_type" parameter
> ---
>  arch/riscv/include/asm/sbi.h | 16 ++++++++++++++++
>  arch/riscv/kernel/sbi.c      | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/sbi.h
> b/arch/riscv/include/asm/sbi.h
> index 653edb25d495..5b2d6d614c20 100644
> --- a/arch/riscv/include/asm/sbi.h
> +++ b/arch/riscv/include/asm/sbi.h
> @@ -27,6 +27,7 @@ enum sbi_ext_id {
>         SBI_EXT_IPI = 0x735049,
>         SBI_EXT_RFENCE = 0x52464E43,
>         SBI_EXT_HSM = 0x48534D,
> +       SBI_EXT_SRST = 0x53525354,
>  };
>  
>  enum sbi_ext_base_fid {
> @@ -70,6 +71,21 @@ enum sbi_hsm_hart_status {
>         SBI_HSM_HART_STATUS_STOP_PENDING,
>  };
>  
> +enum sbi_ext_srst_fid {
> +       SBI_EXT_SRST_RESET = 0,
> +};
> +
> +enum sbi_srst_reset_type {
> +       SBI_SRST_RESET_TYPE_SHUTDOWN = 0,
> +       SBI_SRST_RESET_TYPE_COLD_REBOOT,
> +       SBI_SRST_RESET_TYPE_WARM_REBOOT,
> +};
> +
> +enum sbi_srst_reset_reason {
> +       SBI_SRST_RESET_REASON_NONE = 0,
> +       SBI_SRST_RESET_REASON_SYS_FAILURE,
> +};
> +
>  #define SBI_SPEC_VERSION_DEFAULT       0x1
>  #define SBI_SPEC_VERSION_MAJOR_SHIFT   24
>  #define SBI_SPEC_VERSION_MAJOR_MASK    0x7f
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 226ccce0f9e0..33b834ecd195 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/init.h>
>  #include <linux/pm.h>
> +#include <linux/reboot.h>
>  #include <asm/sbi.h>
>  #include <asm/smp.h>
>  
> @@ -501,6 +502,32 @@ int sbi_remote_hfence_vvma_asid(const unsigned
> long *hart_mask,
>  }
>  EXPORT_SYMBOL(sbi_remote_hfence_vvma_asid);
>  
> +static void sbi_srst_reset(unsigned long type, unsigned long reason)
> +{
> +       sbi_ecall(SBI_EXT_SRST, SBI_EXT_SRST_RESET, type, reason,
> +                 0, 0, 0, 0);
> +       pr_warn("%s: type=0x%lx reason=0x%lx failed\n",
> +               __func__, type, reason);
> +}
> +
> +static int sbi_srst_reboot(struct notifier_block *this,
> +                          unsigned long mode, void *cmd)
> +{
> +       sbi_srst_reset((mode == REBOOT_WARM || mode == REBOOT_SOFT) ?
> +                      SBI_SRST_RESET_TYPE_WARM_REBOOT :
> +                      SBI_SRST_RESET_TYPE_COLD_REBOOT,
> +                      SBI_SRST_RESET_REASON_NONE);
> +       return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block sbi_srst_reboot_nb;
> +
> +static void sbi_srst_power_off(void)
> +{
> +       sbi_srst_reset(SBI_SRST_RESET_TYPE_SHUTDOWN,
> +                      SBI_SRST_RESET_REASON_NONE);
> +}
> +
>  /**
>   * sbi_probe_extension() - Check if an SBI extension ID is supported
> or not.
>   * @extid: The extension ID to be probed.
> @@ -593,6 +620,13 @@ int __init sbi_init(void)
>                 } else {
>                         __sbi_rfence    = __sbi_rfence_v01;
>                 }
> +               if (sbi_probe_extension(SBI_EXT_SRST) > 0) {
> +                       pr_info("SBI v0.2 SRST extension
> detected\n");
> +                       pm_power_off = sbi_srst_power_off;
> +                       sbi_srst_reboot_nb.notifier_call =
> sbi_srst_reboot;
> +                       sbi_srst_reboot_nb.priority = 192;
> +                       register_restart_handler(&sbi_srst_reboot_nb)
> ;
> +               }
>         } else {
>                 __sbi_set_timer = __sbi_set_timer_v01;
>                 __sbi_send_ipi  = __sbi_send_ipi_v01;