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Date:   Sun, 11 Jul 2021 11:59:33 -0700 (PDT)
Subject:     Re: [PATCH v7 1/1] RISC-V: Use SBI SRST extension when available
In-Reply-To: <9ED386A8-60BD-44AE-A3D1-843D3CFDDF8A@wdc.com>
CC:     anup@brainfault.org, Paul Walmsley <paul.walmsley@sifive.com>,
        aou@eecs.berkeley.edu, Atish Patra <Atish.Patra@wdc.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
From:   Palmer Dabbelt <palmerdabbelt@google.com>
To:     Anup Patel <Anup.Patel@wdc.com>
Message-ID: <mhng-6c25dda6-4c85-447c-ad9c-7641f2858b10@palmerdabbelt-glaptop>
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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@brainfault.org> wrote:
> 
>     On Wed, Jul 7, 2021 at 1:57 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>     >
>     > On Mon, 21 Jun 2021 21:46:46 PDT (-0700), anup@brainfault.org wrote:
>     > > Hi Palmer,
>     > >
>     > > On Wed, Jun 9, 2021 at 5:43 PM Anup Patel <anup.patel@wdc.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.

> 
> 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@wdc.com>
>     > >> Reviewed-by: Atish Patra <atish.patra@wdc.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
>     > >>
>