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

[Anup Patel]

> -----Original Message-----
> From: Anup Patel <Anup.Patel at wdc.com>
> Sent: 25 September 2020 17:01
> To: Palmer Dabbelt <palmer at dabbelt.com>; Palmer Dabbelt
> <palmerdabbelt at google.com>; Paul Walmsley <paul.walmsley at sifive.com>;
> Albert Ou <aou at eecs.berkeley.edu>
> Cc: Atish Patra <Atish.Patra at wdc.com>; Alistair Francis
> <Alistair.Francis at wdc.com>; Anup Patel <anup at brainfault.org>; linux-
> riscv at lists.infradead.org; linux-kernel at vger.kernel.org; Anup Patel
> <Anup.Patel at wdc.com>
> Subject: [RFC PATCH] RISC-V: Use SBI SRST extension when available
> 
> 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 draft specification of SBI SRST extension is available in
> srbt_v1 branch of: https://github.com/avpatel/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 |  7 +++++++
>  arch/riscv/kernel/sbi.c      | 25 +++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h index
> 653edb25d495..2fcecec7dd0c 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 +71,12 @@ enum sbi_hsm_hart_status {
>  	SBI_HSM_HART_STATUS_STOP_PENDING,
>  };
> 
> +enum sbi_ext_srst_fid {
> +	SBI_EXT_SRST_SHUTDOWN = 0,
> +	SBI_EXT_SRST_COLD_REBOOT,
> +	SBI_EXT_SRST_WARM_REBOOT
> +};
> +

I referred older SBI SRST extension draft where we have separate
function ID for shutdown, cold reboot, and warm reboot.

I will send v2 patch as-per latest SBI SRST extension draft.

My apologies for the noise.

Regards,
Anup

>  #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..865e028a9a4b 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 +502,23 @@ int sbi_remote_hfence_vvma_asid(const unsigned
> long *hart_mask,  }  EXPORT_SYMBOL(sbi_remote_hfence_vvma_asid);
> 
> +static int sbi_srst_reboot(struct notifier_block *this,
> +			   unsigned long mode, void *cmd)
> +{
> +	sbi_ecall(SBI_EXT_SRST, (mode == REBOOT_WARM || mode ==
> REBOOT_SOFT) ?
> +		  SBI_EXT_SRST_WARM_REBOOT :
> SBI_EXT_SRST_COLD_REBOOT,
> +		  0, 0, 0, 0, 0, 0);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block sbi_srst_reboot_nb;
> +
> +static void sbi_srst_power_off(void)
> +{
> +	sbi_ecall(SBI_EXT_SRST, SBI_EXT_SRST_SHUTDOWN, 0, 0, 0, 0, 0, 0); }
> +
>  /**
>   * sbi_probe_extension() - Check if an SBI extension ID is supported or not.
>   * @extid: The extension ID to be probed.
> @@ -593,6 +611,13 @@ 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;
> --
> 2.25.1