Re: [PATCH v7 1/1] RISC-V: Use SBI SRST extension when available

From: Palmer Dabbelt
Date: Sun Jul 11 2021 - 14:59:53 EST

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On Fri, 09 Jul 2021 22:01:02 PDT (-0700), Anup Patel wrote:

On 08/07/21, 9:22 AM, "Anup Patel" <anup@xxxxxxxxxxxxxx> wrote:

On Wed, Jul 7, 2021 at 1:57 AM Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx> wrote:
>
> On Mon, 21 Jun 2021 21:46:46 PDT (-0700), anup@xxxxxxxxxxxxxx wrote:
> > Hi Palmer,
> >
> > On Wed, Jun 9, 2021 at 5:43 PM Anup Patel <anup.patel@xxxxxxx> 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 the SBI v0.3 specification.
> >> (Refer, https://github.com/riscv/riscv-sbi-doc/releases/tag/v0.3.0-rc1)
> >
> > Can you please consider this patch for Linux-5.14-rc1 ?
> >
> > The SBI v0.3 spec is already frozen and this patch has been
> > floating on LKML for quite a few months now.
>
> I didn't realize that SBI-0.3 had been frozed. That link is to a RC,
> the cooresponding v0.3.0 tag isn't in that repo. Can you give me a
> pointer to the frozen spec?

Here's the link to SBI v0.3.0 tag:
https://github.com/riscv/riscv-sbi-doc/releases/tag/v0.3.0

We treat RC tags as frozen in SBI spec because no functional
changes are done in SBI spec after it is tagged as RC. We only
do typo fixes and clarifications on SBI spec RC release.

Treating the 0.3.0-rc1 as frozen as soon as it's released is a terrifying policy: some of the fixes I sent in after I saw rc1 released change the actual meaning of the text, even if they were meant to change them to what I thought the intended meaning was supposed to be. That means the actual text of 0.3.0-rc1 and 0.3.0 conflict with each other. Given that frozen comes with a guarntee of backwards compatibility, does that mean that the behavior allowed by 0.3.0-rc1 is compliant with the SBI, even if it was likely just allowed by a wording mistake?

If you're going to freeze things at rc1 then you really need to be quite explicit about that, as generally the point of RCs is to elicit review/testing. Looks like I was the only person to have provided any review, so I guess I was the only one who assumed "We don't expect any significant functional changes. We will wait for any further feedback and release the official v0.3 in a month or so." actually meant "this is frozen".

Can you take this patch for Linux-5.14 ??

No, sorry, it's way too late for that. Please be specific about when you freeze specifications in the future, so we can all stay on the same page.

Regards,
Anup

Regards,
Anup

>
> >
> > Regards,
> > Anup
> >
> >>
> >> This patch extends Linux RISC-V SBI implementation to detect
> >> and use SBI SRST extension.
> >>
> >> Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> >> Reviewed-by: Atish Patra <atish.patra@xxxxxxx>
> >> ---
> >> arch/riscv/include/asm/sbi.h | 24 ++++++++++++++++++++++++
> >> arch/riscv/kernel/sbi.c | 35 +++++++++++++++++++++++++++++++++++
> >> 2 files changed, 59 insertions(+)
> >>
> >> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> >> index 0d42693cb65e..289621da4a2a 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
> >> @@ -148,6 +164,14 @@ static inline unsigned long sbi_minor_version(void)
> >> return sbi_spec_version & SBI_SPEC_VERSION_MINOR_MASK;
> >> }
> >>
> >> +/* Make SBI version */
> >> +static inline unsigned long sbi_mk_version(unsigned long major,
> >> + unsigned long minor)
> >> +{
> >> + return ((major & SBI_SPEC_VERSION_MAJOR_MASK) <<
> >> + SBI_SPEC_VERSION_MAJOR_SHIFT) | minor;
> >> +}
> >> +
> >> int sbi_err_map_linux_errno(int err);
> >> #else /* CONFIG_RISCV_SBI */
> >> static inline int sbi_remote_fence_i(const unsigned long *hart_mask) { return -1; }
> >> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> >> index 7402a417f38e..9a84f0cb5175 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.
> >> @@ -608,6 +635,14 @@ void __init sbi_init(void)
> >> } else {
> >> __sbi_rfence = __sbi_rfence_v01;
> >> }
> >> + if ((sbi_spec_version >= sbi_mk_version(0, 3)) &&
> >> + (sbi_probe_extension(SBI_EXT_SRST) > 0)) {
> >> + 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;
> >> --
> >> 2.25.1
> >>

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Previous message: Palmer Dabbelt: "Re: [GIT PULL] RISC-V Patches for the 5.14 Merge Window, Part 1"
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