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Message-ID: <mhng-40d64bc7-5a95-4a16-af45-1d7fd7c6167e@palmerdabbelt-glaptop>
Date: Wed, 28 Jul 2021 21:30:19 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: Anup Patel <Anup.Patel@....com>
CC: anup@...infault.org, Paul Walmsley <paul.walmsley@...ive.com>,
aou@...s.berkeley.edu, Atish Patra <Atish.Patra@....com>,
Alistair Francis <Alistair.Francis@....com>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/1] RISC-V: Use SBI SRST extension when available
On Sun, 11 Jul 2021 11:59:33 PDT (-0700), Palmer Dabbelt wrote:
> On Fri, 09 Jul 2021 22:01:02 PDT (-0700), Anup Patel wrote:
>>
>>
>> On 08/07/21, 9:22 AM, "Anup Patel" <anup@...infault.org> wrote:
>>
>> On Wed, Jul 7, 2021 at 1:57 AM Palmer Dabbelt <palmerdabbelt@...gle.com> wrote:
>> >
>> > On Mon, 21 Jun 2021 21:46:46 PDT (-0700), anup@...infault.org wrote:
>> > > Hi Palmer,
>> > >
>> > > On Wed, Jun 9, 2021 at 5:43 PM Anup Patel <anup.patel@....com> 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.
I went and talked to Krste, and he says that there's a whole process for
freezing extensions that this hasn't gone through. They don't have
anything written down that I can point to, but can you guys please just
get on the same page about this? It seems like every time I talk to
someone from the RISC-V foundation I get a conflicting description of
what's going on, and I'm entirely out of patience when it comes to
getting blamed for all the chaos over there.
>
>>
>> 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@....com>
>> > >> Reviewed-by: Atish Patra <atish.patra@....com>
>> > >> ---
>> > >> 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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