[PATCH v4] RISC-V: Use SBI SRST extension when available

[Palmer Dabbelt]

On Mon, 01 Mar 2021 03:58:33 PST (-0800), 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 at wdc.com>
> ---
>  arch/riscv/include/asm/sbi.h | 16 ++++++++++++++
>  arch/riscv/kernel/sbi.c      | 41 +++++++++++++++++++++++++++++++++---
>  2 files changed, 54 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> index 99895d9c3bdd..8add0209c9c7 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 f4a7db3d309e..49155588e56c 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.
> @@ -577,22 +604,30 @@ void __init sbi_init(void)
>  			sbi_get_firmware_id(), sbi_get_firmware_version());
>  		if (sbi_probe_extension(SBI_EXT_TIME) > 0) {
>  			__sbi_set_timer = __sbi_set_timer_v02;
> -			pr_info("SBI v0.2 TIME extension detected\n");
> +			pr_info("SBI TIME extension detected\n");
>  		} else {
>  			__sbi_set_timer = __sbi_set_timer_v01;
>  		}
>  		if (sbi_probe_extension(SBI_EXT_IPI) > 0) {
>  			__sbi_send_ipi	= __sbi_send_ipi_v02;
> -			pr_info("SBI v0.2 IPI extension detected\n");
> +			pr_info("SBI IPI extension detected\n");

These aren't really part of the reset stuff and should be split into a separate 
patch.

>  		} else {
>  			__sbi_send_ipi	= __sbi_send_ipi_v01;
>  		}
>  		if (sbi_probe_extension(SBI_EXT_RFENCE) > 0) {
>  			__sbi_rfence	= __sbi_rfence_v02;
> -			pr_info("SBI v0.2 RFENCE extension detected\n");
> +			pr_info("SBI RFENCE extension detected\n");
>  		} else {
>  			__sbi_rfence	= __sbi_rfence_v01;
>  		}
> +		if (sbi_probe_extension(SBI_EXT_SRST) > 0 &&
> +		    sbi_minor_version() >= 3) {
> +			pr_info("SBI 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;

This is fine, but I don't want to take things for draft SBI versions until 
they're at least tagged.