Re: [RFC PATCH 2/2] RISC-V: Add basic support for SBI v0.2

[Anup Patel <anup@brainfault.org>]

On Tue, Aug 27, 2019 at 1:28 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Mon, Aug 26, 2019 at 04:32:56PM -0700, Atish Patra wrote:
> > The SBI v0.2 introduces a base extension which is backward compatible
> > with v0.1. Implement all helper functions and minimum required SBI
> > calls from v0.2 for now. All other base extension function will be
> > added later as per need.
> >
> > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > ---
> >  arch/riscv/include/asm/sbi.h | 68 +++++++++++++++++++++++++++++-------
> >  arch/riscv/kernel/Makefile   |  1 +
> >  arch/riscv/kernel/sbi.c      | 50 ++++++++++++++++++++++++++
> >  arch/riscv/kernel/setup.c    |  2 ++
> >  4 files changed, 108 insertions(+), 13 deletions(-)
> >  create mode 100644 arch/riscv/kernel/sbi.c
> >
> > diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> > index 7f5ecaaaa0d7..4a4476956693 100644
> > --- a/arch/riscv/include/asm/sbi.h
> > +++ b/arch/riscv/include/asm/sbi.h
> > @@ -8,7 +8,6 @@
> >
> >  #include <linux/types.h>
> >
> > -
> >  #define SBI_EXT_LEGACY_SET_TIMER 0x0
> >  #define SBI_EXT_LEGACY_CONSOLE_PUTCHAR 0x1
> >  #define SBI_EXT_LEGACY_CONSOLE_GETCHAR 0x2
> > @@ -19,28 +18,61 @@
> >  #define SBI_EXT_LEGACY_REMOTE_SFENCE_VMA_ASID 0x7
> >  #define SBI_EXT_LEGACY_SHUTDOWN 0x8
> >
> > -#define SBI_CALL_LEGACY(which, arg0, arg1, arg2, arg3) ({             \
> > +#define SBI_EXT_BASE 0x10
> > +
> > +enum sbi_ext_base_fid {
> > +     SBI_EXT_BASE_GET_SPEC_VERSION = 0,
> > +     SBI_EXT_BASE_GET_IMP_ID,
> > +     SBI_EXT_BASE_GET_IMP_VERSION,
> > +     SBI_EXT_BASE_PROBE_EXT,
> > +     SBI_EXT_BASE_GET_MVENDORID,
> > +     SBI_EXT_BASE_GET_MARCHID,
> > +     SBI_EXT_BASE_GET_MIMPID,
> > +};
> > +
> > +#define SBI_CALL_LEGACY(ext, fid, arg0, arg1, arg2, arg3) ({ \
> >       register uintptr_t a0 asm ("a0") = (uintptr_t)(arg0);   \
> >       register uintptr_t a1 asm ("a1") = (uintptr_t)(arg1);   \
> >       register uintptr_t a2 asm ("a2") = (uintptr_t)(arg2);   \
> >       register uintptr_t a3 asm ("a3") = (uintptr_t)(arg3);   \
> > -     register uintptr_t a7 asm ("a7") = (uintptr_t)(which);  \
> > +     register uintptr_t a6 asm ("a6") = (uintptr_t)(fid);    \
> > +     register uintptr_t a7 asm ("a7") = (uintptr_t)(ext);    \
> >       asm volatile ("ecall"                                   \
> > -                   : "+r" (a0)                               \
> > -                   : "r" (a1), "r" (a2), "r" (a3), "r" (a7)  \
> > +                   : "+r" (a0), "+r" (a1)                    \
> > +                   : "r" (a2), "r" (a3), "r" (a6), "r" (a7) \
>
> Maybe I'm missing something, but how is this supposed to work on systems
> with SBI v0.1? Wouldn't this cause a mismatch in the registers?

The SBI v0.2 has two major changes:
1. New improved calling convention which is backward compatible
with SBI v0.1 so older kernels with SBI v0.1 will continue to work as-is.
2. Base set of mandatory SBI v0.2 calls which can be used to detect
SBI version, check supported SBI calls and extentions.

Old calling convention in SBI v0.1 was:
Parameters:
a0 -> arg0
a1 -> arg1
a2 -> arg2
a3 -> arg3
a7 -> function_id
Return:
a0 -> return value or error code

In SBI v0.2, we have extension and function. Each SBI extension
is a set of function. The new calling convention in SBI v0.2 is:
Parameters:
a0 -> arg0
a1 -> arg1
a2 -> arg2
a3 -> arg3
a6 -> function_id
a7 -> extension_id
Return:
a0 -> error code
a1 -> return value (optional)

All legacy SBI v0.1 functions can be thought of as separate
extensions. That's how SBI v0.2 will be backward compatible.

Regards,
Anup

>
> >                     : "memory");                              \
> >       a0;                                                     \
> >  })
> >
> >  /* Lazy implementations until SBI is finalized */
> > -#define SBI_CALL_LEGACY_0(which) SBI_CALL_LEGACY(which, 0, 0, 0, 0)
> > -#define SBI_CALL_LEGACY_1(which, arg0) SBI_CALL_LEGACY(which, arg0, 0, 0, 0)
> > -#define SBI_CALL_LEGACY_2(which, arg0, arg1) \
> > -             SBI_CALL_LEGACY(which, arg0, arg1, 0, 0)
> > -#define SBI_CALL_LEGACY_3(which, arg0, arg1, arg2) \
> > -             SBI_CALL_LEGACY(which, arg0, arg1, arg2, 0)
> > -#define SBI_CALL_LEGACY_4(which, arg0, arg1, arg2, arg3) \
> > -             SBI_CALL_LEGACY(which, arg0, arg1, arg2, arg3)
> > +#define SBI_CALL_LEGACY_0(ext) SBI_CALL_LEGACY(ext, 0, 0, 0, 0, 0)
> > +#define SBI_CALL_LEGACY_1(ext, arg0) SBI_CALL_LEGACY(ext, 0, arg0, 0, 0, 0)
> > +#define SBI_CALL_LEGACY_2(ext, arg0, arg1) \
> > +             SBI_CALL_LEGACY(ext, 0, arg0, arg1, 0, 0)
> > +#define SBI_CALL_LEGACY_3(ext, arg0, arg1, arg2) \
> > +             SBI_CALL_LEGACY(ext, 0, arg0, arg1, arg2, 0)
> > +#define SBI_CALL_LEGACY_4(ext, arg0, arg1, arg2, arg3) \
> > +             SBI_CALL_LEGACY(ext, 0, arg0, arg1, arg2, arg3)
> > +
> > +extern unsigned long sbi_firmware_version;
> > +struct sbiret {
> > +     long error;
> > +     long value;
> > +};
> > +
> > +void riscv_sbi_init(void);
> > +struct sbiret riscv_sbi_ecall(int ext, int fid, int arg0, int arg1,
> > +                            int arg2, int arg3);
> > +
> > +#define SBI_CALL_0(ext, fid) riscv_sbi_ecall(ext, fid, 0, 0, 0, 0)
> > +#define SBI_CALL_1(ext, fid, arg0) riscv_sbi_ecall(ext, fid, arg0, 0, 0, 0)
> > +#define SBI_CALL_2(ext, fid, arg0, arg1) \
> > +             riscv_sbi_ecall(ext, fid, arg0, arg1, 0, 0)
> > +#define SBI_CALL_3(ext, fid, arg0, arg1, arg2) \
> > +             riscv_sbi_ecall(ext, fid, arg0, arg1, arg2, 0)
> > +#define SBI_CALL_4(ext, fid, arg0, arg1, arg2, arg3) \
> > +             riscv_sbi_ecall(ext, fid, arg0, arg1, arg2, arg3)
> > +
> >
> >  static inline void sbi_console_putchar(int ch)
> >  {
> > @@ -99,4 +131,14 @@ static inline void sbi_remote_sfence_vma_asid(const unsigned long *hart_mask,
> >                         start, size, asid);
> >  }
> >
> > +static inline unsigned long riscv_sbi_major_version(void)
> > +{
> > +     return (sbi_firmware_version >> 24) & 0x7f;
> > +}
> > +
> > +static inline unsigned long riscv_sbi_minor_version(void)
> > +{
> > +     return sbi_firmware_version & 0xffffff;
> > +}
> > +
> >  #endif
> > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> > index 2420d37d96de..faf862d26924 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -17,6 +17,7 @@ obj-y       += irq.o
> >  obj-y        += process.o
> >  obj-y        += ptrace.o
> >  obj-y        += reset.o
> > +obj-y        += sbi.o
> >  obj-y        += setup.o
> >  obj-y        += signal.o
> >  obj-y        += syscall_table.o
> > diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> > new file mode 100644
> > index 000000000000..457b8cc0e9d9
> > --- /dev/null
> > +++ b/arch/riscv/kernel/sbi.c
> > @@ -0,0 +1,50 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * SBI initialilization and base extension implementation.
> > + *
> > + * Copyright (c) 2019 Western Digital Corporation or its affiliates.
> > + */
> > +
> > +#include <asm/sbi.h>
> > +#include <linux/sched.h>
> > +
> > +unsigned long sbi_firmware_version;
> > +
> > +struct sbiret riscv_sbi_ecall(int ext, int fid, int arg0, int arg1,
> > +                          int arg2, int arg3)
> > +{
> > +     struct sbiret ret;
> > +
> > +     register uintptr_t a0 asm ("a0") = (uintptr_t)(arg0);
> > +     register uintptr_t a1 asm ("a1") = (uintptr_t)(arg1);
> > +     register uintptr_t a2 asm ("a2") = (uintptr_t)(arg2);
> > +     register uintptr_t a3 asm ("a3") = (uintptr_t)(arg3);
> > +     register uintptr_t a6 asm ("a6") = (uintptr_t)(fid);
> > +     register uintptr_t a7 asm ("a7") = (uintptr_t)(ext);
> > +     asm volatile ("ecall"
> > +                   : "+r" (a0), "+r" (a1)
> > +                   : "r" (a2), "r" (a3), "r" (a6), "r" (a7)
> > +                   : "memory");
> > +     ret.error = a0;
> > +     ret.value = a1;
> > +
> > +     return ret;
> > +}
> > +
> > +static struct sbiret sbi_get_spec_version(void)
> > +{
> > +     return SBI_CALL_0(SBI_EXT_BASE, SBI_EXT_BASE_GET_SPEC_VERSION);
> > +}
> > +
> > +void riscv_sbi_init(void)
> > +{
> > +     struct sbiret ret;
> > +
> > +     /* legacy SBI version*/
> > +     sbi_firmware_version = 0x1;
> > +     ret = sbi_get_spec_version();
> > +     if (!ret.error)
> > +             sbi_firmware_version = ret.value;
> > +     pr_info("SBI version implemented in firmware [%lu:%lu]\n",
> > +             riscv_sbi_major_version(), riscv_sbi_minor_version());
> > +}
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index a990a6cb184f..4c324fd398c8 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -21,6 +21,7 @@
> >  #include <asm/sections.h>
> >  #include <asm/pgtable.h>
> >  #include <asm/smp.h>
> > +#include <asm/sbi.h>
> >  #include <asm/tlbflush.h>
> >  #include <asm/thread_info.h>
> >
> > @@ -70,6 +71,7 @@ void __init setup_arch(char **cmdline_p)
> >       swiotlb_init(1);
> >  #endif
> >
> > +     riscv_sbi_init();
> >  #ifdef CONFIG_SMP
> >       setup_smp();
> >  #endif
> > --
> > 2.21.0
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
> --
> Sincerely yours,
> Mike.
>