Re: [PATCH v4] RISC-V: Add Zawrs ISA extension support

[Alistair Francis <alistair23@gmail.com>]

On Thu, Oct 6, 2022 at 12:52 AM Christoph Muellner
<christoph.muellner@vrull.eu> wrote:
>
> This patch adds support for the Zawrs ISA extension.
> Given the current (incomplete) implementation of reservation sets
> there seems to be no way to provide a full emulation of the WRS
> instruction (wake on reservation set invalidation or timeout or
> interrupt). Therefore, we just exit the TB and return to the main loop.
>
> The specification can be found here:
>   https://github.com/riscv/riscv-zawrs/blob/main/zawrs.adoc
>
> Note, that the Zawrs extension is frozen, but not ratified yet.
>
> Changes since v3:
> * Remove "RFC" since the extension is frozen
> * Rebase on master and fix integration issues
> * Fix entry ordering in extension list
>
> Changes since v2:
> * Rebase on master and resolve conflicts
> * Adjustments according to a specification change
> * Inline REQUIRE_ZAWRS() since it has only one user
>
> Changes since v1:
> * Adding zawrs to the ISA string that is passed to the kernel
>
> Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu.c                          |  7 +++
>  target/riscv/cpu.h                          |  1 +
>  target/riscv/insn32.decode                  |  4 ++
>  target/riscv/insn_trans/trans_rvzawrs.c.inc | 51 +++++++++++++++++++++
>  target/riscv/translate.c                    |  1 +
>  5 files changed, 64 insertions(+)
>  create mode 100644 target/riscv/insn_trans/trans_rvzawrs.c.inc
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index b29c88b9f0..b08ce94ba6 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -76,6 +76,7 @@ static const struct isa_ext_data isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(zicsr, true, PRIV_VERSION_1_10_0, ext_icsr),
>      ISA_EXT_DATA_ENTRY(zifencei, true, PRIV_VERSION_1_10_0, ext_ifencei),
>      ISA_EXT_DATA_ENTRY(zihintpause, true, PRIV_VERSION_1_10_0, ext_zihintpause),
> +    ISA_EXT_DATA_ENTRY(zawrs, true, PRIV_VERSION_1_12_0, ext_zawrs),
>      ISA_EXT_DATA_ENTRY(zfh, true, PRIV_VERSION_1_12_0, ext_zfh),
>      ISA_EXT_DATA_ENTRY(zfhmin, true, PRIV_VERSION_1_12_0, ext_zfhmin),
>      ISA_EXT_DATA_ENTRY(zfinx, true, PRIV_VERSION_1_12_0, ext_zfinx),
> @@ -744,6 +745,11 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
>              return;
>          }
>
> +        if ((cpu->cfg.ext_zawrs) && !cpu->cfg.ext_a) {
> +            error_setg(errp, "Zawrs extension requires A extension");
> +            return;
> +        }
> +
>          if ((cpu->cfg.ext_zfh || cpu->cfg.ext_zfhmin) && !cpu->cfg.ext_f) {
>              error_setg(errp, "Zfh/Zfhmin extensions require F extension");
>              return;
> @@ -999,6 +1005,7 @@ static Property riscv_cpu_extensions[] = {
>      DEFINE_PROP_BOOL("Zifencei", RISCVCPU, cfg.ext_ifencei, true),
>      DEFINE_PROP_BOOL("Zicsr", RISCVCPU, cfg.ext_icsr, true),
>      DEFINE_PROP_BOOL("Zihintpause", RISCVCPU, cfg.ext_zihintpause, true),
> +    DEFINE_PROP_BOOL("Zawrs", RISCVCPU, cfg.ext_zawrs, true),
>      DEFINE_PROP_BOOL("Zfh", RISCVCPU, cfg.ext_zfh, false),
>      DEFINE_PROP_BOOL("Zfhmin", RISCVCPU, cfg.ext_zfhmin, false),
>      DEFINE_PROP_BOOL("Zve32f", RISCVCPU, cfg.ext_zve32f, false),
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index b131fa8c8e..2b87966373 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -446,6 +446,7 @@ struct RISCVCPUConfig {
>      bool ext_svnapot;
>      bool ext_svpbmt;
>      bool ext_zdinx;
> +    bool ext_zawrs;
>      bool ext_zfh;
>      bool ext_zfhmin;
>      bool ext_zfinx;
> diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
> index d0253b8104..b7e7613ea2 100644
> --- a/target/riscv/insn32.decode
> +++ b/target/riscv/insn32.decode
> @@ -718,6 +718,10 @@ vsetvli         0 ........... ..... 111 ..... 1010111  @r2_zimm11
>  vsetivli        11 .......... ..... 111 ..... 1010111  @r2_zimm10
>  vsetvl          1000000 ..... ..... 111 ..... 1010111  @r
>
> +# *** Zawrs Standard Extension ***
> +wrs_nto    000000001101 00000 000 00000 1110011
> +wrs_sto    000000011101 00000 000 00000 1110011
> +
>  # *** RV32 Zba Standard Extension ***
>  sh1add     0010000 .......... 010 ..... 0110011 @r
>  sh2add     0010000 .......... 100 ..... 0110011 @r
> diff --git a/target/riscv/insn_trans/trans_rvzawrs.c.inc b/target/riscv/insn_trans/trans_rvzawrs.c.inc
> new file mode 100644
> index 0000000000..f0da2fe50a
> --- /dev/null
> +++ b/target/riscv/insn_trans/trans_rvzawrs.c.inc
> @@ -0,0 +1,51 @@
> +/*
> + * RISC-V translation routines for the RISC-V Zawrs Extension.
> + *
> + * Copyright (c) 2022 Christoph Muellner, christoph.muellner@vrull.io
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2 or later, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +static bool trans_wrs(DisasContext *ctx)
> +{
> +    if (!ctx->cfg_ptr->ext_zawrs) {
> +        return false;
> +    }
> +
> +    /*
> +     * The specification says:
> +     * While stalled, an implementation is permitted to occasionally
> +     * terminate the stall and complete execution for any reason.
> +     *
> +     * So let's just exit TB and return to the main loop.
> +     */
> +
> +    /* Clear the load reservation  (if any).  */
> +    tcg_gen_movi_tl(load_res, -1);
> +
> +    gen_set_pc_imm(ctx, ctx->pc_succ_insn);
> +    tcg_gen_exit_tb(NULL, 0);
> +    ctx->base.is_jmp = DISAS_NORETURN;
> +
> +    return true;
> +}
> +
> +#define GEN_TRANS_WRS(insn)                                            \
> +static bool trans_ ## insn(DisasContext *ctx, arg_ ## insn *a)         \
> +{                                                                      \
> +       (void)a;                                                        \
> +       return trans_wrs(ctx);                                          \
> +}
> +
> +GEN_TRANS_WRS(wrs_nto)
> +GEN_TRANS_WRS(wrs_sto)
> diff --git a/target/riscv/translate.c b/target/riscv/translate.c
> index db123da5ec..e22de88e97 100644
> --- a/target/riscv/translate.c
> +++ b/target/riscv/translate.c
> @@ -1029,6 +1029,7 @@ static uint32_t opcode_at(DisasContextBase *dcbase, target_ulong pc)
>  #include "insn_trans/trans_rvh.c.inc"
>  #include "insn_trans/trans_rvv.c.inc"
>  #include "insn_trans/trans_rvb.c.inc"
> +#include "insn_trans/trans_rvzawrs.c.inc"
>  #include "insn_trans/trans_rvzfh.c.inc"
>  #include "insn_trans/trans_rvk.c.inc"
>  #include "insn_trans/trans_privileged.c.inc"
> --
> 2.37.3
>
>