Re: [PATCH v5] target/riscv: Add isa extenstion strings to the device tree

[Atish Kumar Patra]

On Tue, Mar 15, 2022 at 2:17 AM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> On Tue, Mar 15, 2022 at 7:43 AM Atish Patra <atishp@rivosinc.com> wrote:
> >
> > The Linux kernel parses the ISA extensions from "riscv,isa" DT
> > property. It used to parse only the single letter base extensions
> > until now. A generic ISA extension parsing framework was proposed[1]
> > recently that can parse multi-letter ISA extensions as well.
> >
> > Generate the extended ISA string by appending  the available ISA extensions
>
> nits: remove one space after "appending"
>

Will fix it.

> > to the "riscv,isa" string if it is enabled so that kernel can process it.
> >
> > [1] https://lkml.org/lkml/2022/2/15/263
>
> Could you please post a link to the "riscv,isa" DT bindings spec or
> discussion thread? It seems not mentioned in the above LKML thread.
>

Latest discussion on the discussion:
https://lkml.org/lkml/2022/3/10/1416

riscv,isa DT binding:
https://elixir.bootlin.com/linux/v5.17-rc8/source/Documentation/devicetree/bindings/riscv/cpus.yaml#L66

> >
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
> > Suggested-by: Heiko Stubner <heiko@sntech.de>
> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
> > ---
> > Changes from v4->v5:
> > 1. Fixed the order of Zxx extensions.
> > 2. Added a comment clearly describing the rules of extension order.
> >
> > Changes from v3->v4:
> > 1. Fixed the order of the extension names.
> > 2. Added all the available ISA extensions in Qemu.
> >
> > Changes from v2->v3:
> > 1. Used g_strconcat to replace snprintf & a max isa string length as
> > suggested by Anup.
> > 2. I have not included the Tested-by Tag from Heiko because the
> > implementation changed from v2 to v3.
> >
> > Changes from v1->v2:
> > 1. Improved the code redability by using arrays instead of individual check
> > ---
> >  target/riscv/cpu.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 61 insertions(+)
> >
> > diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> > index ddda4906ffb7..097c42f5c50f 100644
> > --- a/target/riscv/cpu.c
> > +++ b/target/riscv/cpu.c
> > @@ -34,6 +34,12 @@
> >
> >  /* RISC-V CPU definitions */
> >
> > +/* This includes the null terminated character '\0' */
> > +struct isa_ext_data {
> > +        const char *name;
> > +        bool enabled;
> > +};
> > +
> >  static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
> >
> >  const char * const riscv_int_regnames[] = {
> > @@ -898,6 +904,60 @@ static void riscv_cpu_class_init(ObjectClass *c, void 
> > *data)
> >      device_class_set_props(dc, riscv_cpu_properties);
> >  }
> >
> > +#define ISA_EDATA_ENTRY(name, prop) {#name, cpu->cfg.prop}
> > +
> > +static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int 
> > max_str_len)
> > +{
> > +    char *old = *isa_str;
> > +    char *new = *isa_str;
> > +    int i;
> > +
> > +    /**
> > +     * Here are the ordering rules of extension naming defined by RISC-V
> > +     * specification :
> > +     * 1. All extensions should be separated from other multi-letter 
> > extensions
> > +     *    from other multi-letter extensions by an underscore.
>
> redundant "from other multi-letter extensions"
>

Oops. Will fix it.

> > +     * 2. The first letter following the 'Z' conventionally indicates the 
> > most
>
> Should this be lower case "z"?

Nope. I am just iterating the rules defined by the spec. The device
tree has lower case 'z'
as per the device binding which mandates all lower case.

>
> > +     *    closely related alphabetical extension category, IMAFDQLCBKJTPVH.
> > +     *    If multiple 'Z' extensions are named, they should be ordered 
> > first
> > +     *    by category, then alphabetically within a category.
> > +     * 3. Standard supervisor-level extensions (starts with 'S') should be
>
> lower case "s"?

Same reasoning as above.

>
> > +     *    listed after standard unprivileged extensions.  If multiple
> > +     *    supervisor-level extensions are listed, they should be ordered
> > +     *    alphabetically.
> > +     * 4. Non-standard extensions (starts with 'X') must be listed after 
> > all
> > +     *    standard extensions. They must be separated from other 
> > multi-letter
> > +     *    extensions by an underscore.
> > +     */
> > +    struct isa_ext_data isa_edata_arr[] = {
> > +        ISA_EDATA_ENTRY(zfh, ext_zfhmin),
>
> This should be (zfh, ext_zfh)

Yeah. It's a typo. Thanks for catching it.

>
> > +        ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
> > +        ISA_EDATA_ENTRY(zfinx, ext_zfinx),
> > +        ISA_EDATA_ENTRY(zdinx, ext_zdinx),
>
> Should "zdinx" come before "zfinx" *alphabetically* ?

As per the ISA naming rules,

"The first letter following the 'Z' conventionally indicates the most
closely related alphabetical extension category, IMAFDQLCBKJTPVH.
If multiple 'Z' extensions are named, they should be ordered first
by category, then alphabetically within a category."

That's why, zfinx comes before zdinx.
>
> > +        ISA_EDATA_ENTRY(zba, ext_zba),
> > +        ISA_EDATA_ENTRY(zbb, ext_zbb),
> > +        ISA_EDATA_ENTRY(zbc, ext_zbc),
> > +        ISA_EDATA_ENTRY(zbs, ext_zbs),
>
> I don't understand why "zb*" come after "zf*". Alphabetically they
> should come before.
>

Same reasoning as above. But for one category, they are ordered alphabetically.
That's why you see ext_zba, ext_zbb, ext_zbc, ext_zbs in alphabetical order.

> > +        ISA_EDATA_ENTRY(zve32f, ext_zve32f),
> > +        ISA_EDATA_ENTRY(zve64f, ext_zve64f),
> > +        ISA_EDATA_ENTRY(zhinx, ext_zhinx),
> > +        ISA_EDATA_ENTRY(zhinxmin, ext_zhinxmin),
> > +        ISA_EDATA_ENTRY(svinval, ext_svinval),
> > +        ISA_EDATA_ENTRY(svnapot, ext_svnapot),
> > +        ISA_EDATA_ENTRY(svpbmt, ext_svpbmt),
> > +    };
> > +
> > +    for (i = 0; i < ARRAY_SIZE(isa_edata_arr); i++) {
> > +        if (isa_edata_arr[i].enabled) {
> > +            new = g_strconcat(old, "_", isa_edata_arr[i].name, NULL);
> > +            g_free(old);
> > +            old = new;
> > +        }
> > +    }
> > +
> > +    *isa_str = new;
> > +}
> > +
> >  char *riscv_isa_string(RISCVCPU *cpu)
> >  {
> >      int i;
> > @@ -910,6 +970,7 @@ char *riscv_isa_string(RISCVCPU *cpu)
> >          }
> >      }
> >      *p = '\0';
> > +    riscv_isa_string_ext(cpu, &isa_str, maxlen);
> >      return isa_str;
> >  }
> >
>
> Regards,
> Bin