Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220819140250.3892995-1-ajones@ventanamicro.com> <20220819140250.3892995-3-ajones@ventanamicro.com>
In-Reply-To: <20220819140250.3892995-3-ajones@ventanamicro.com>
From:   Anup Patel <anup@brainfault.org>
Date:   Mon, 29 Aug 2022 14:01:06 +0530
Message-ID: <CAAhSdy3KcjR-jFTxH-oYEw=mLTSdbMnadoLcygDPQaa0h3JbxQ@mail.gmail.com>
Subject: Re: [PATCH 2/4] riscv: Introduce support for defining instructions
To:     Andrew Jones <ajones@ventanamicro.com>
Cc:     linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, paul.walmsley@sifive.com,
        palmer@dabbelt.com, aou@eecs.berkeley.edu,
        mchitale@ventanamicro.com, heiko@sntech.de
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Aug 19, 2022 at 7:32 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> When compiling with toolchains that haven't yet been taught about
> new instructions we need to encode them ourselves. Create a new file
> where support for instruction definitions will evolve. We initiate
> the file with a macro called INSN_R(), which implements the R-type
> instruction encoding. INSN_R() will use the assembler's .insn
> directive when available, which should give the assembler a chance
> to do some validation. When .insn is not available we fall back to
> manual encoding.
>
> Not only should using instruction encoding macros improve readability
> and maintainability of code over the alternative of inserting
> instructions directly (e.g. '.word 0xc0de'), but we should also gain
> potential for more optimized code after compilation because the
> compiler will have control over the input and output registers used.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>  arch/riscv/Kconfig                |  3 ++
>  arch/riscv/include/asm/insn-def.h | 82 +++++++++++++++++++++++++++++++
>  2 files changed, 85 insertions(+)
>  create mode 100644 arch/riscv/include/asm/insn-def.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index ed66c31e4655..f8f3b316b838 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -227,6 +227,9 @@ config RISCV_DMA_NONCOHERENT
>         select ARCH_HAS_SETUP_DMA_OPS
>         select DMA_DIRECT_REMAP
>
> +config AS_HAS_INSN
> +       def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
> +
>  source "arch/riscv/Kconfig.socs"
>  source "arch/riscv/Kconfig.erratas"
>
> diff --git a/arch/riscv/include/asm/insn-def.h b/arch/riscv/include/asm/insn-def.h
> new file mode 100644
> index 000000000000..4cd0208068dd
> --- /dev/null
> +++ b/arch/riscv/include/asm/insn-def.h
> @@ -0,0 +1,82 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef __ASM_INSN_DEF_H
> +#define __ASM_INSN_DEF_H

Add a new line here.

> +#include <asm/asm.h>
> +
> +#define INSN_R_FUNC7_SHIFT             25
> +#define INSN_R_RS2_SHIFT               20
> +#define INSN_R_RS1_SHIFT               15
> +#define INSN_R_FUNC3_SHIFT             12
> +#define INSN_R_RD_SHIFT                         7
> +#define INSN_R_OPCODE_SHIFT             0
> +
> +#ifdef __ASSEMBLY__
> +
> +#ifdef CONFIG_AS_HAS_INSN
> +
> +       .macro insn_r, opcode, func3, func7, rd, rs1, rs2
> +       .insn   r \opcode, \func3, \func7, \rd, \rs1, \rs2
> +       .endm

Maybe use indentation here ?

.macro <xyz>
     .insn ...
.endm

> +
> +#else
> +
> +#include <asm/gpr-num.h>
> +
> +       .macro insn_r, opcode, func3, func7, rd, rs1, rs2
> +       .4byte  ((\opcode << INSN_R_OPCODE_SHIFT) |             \
> +                (\func3 << INSN_R_FUNC3_SHIFT) |               \
> +                (\func7 << INSN_R_FUNC7_SHIFT) |               \
> +                (.L__gpr_num_\rd << INSN_R_RD_SHIFT) |         \
> +                (.L__gpr_num_\rs1 << INSN_R_RS1_SHIFT) |       \
> +                (.L__gpr_num_\rs2 << INSN_R_RS2_SHIFT))
> +        .endm
> +
> +#endif
> +
> +#define INSN_R(...)    insn_r __VA_ARGS__
> +
> +#else /* ! __ASSEMBLY__ */
> +
> +#ifdef CONFIG_AS_HAS_INSN
> +
> +#define INSN_R(opcode, func3, func7, rd, rs1, rs2)     \
> +       ".insn  r " opcode ", " func3 ", " func7 ", " rd ", " rs1 ", " rs2 "\n"
> +
> +#else
> +
> +#include <linux/stringify.h>
> +#include <asm/gpr-num.h>
> +
> +#define DEFINE_INSN_R                                                  \
> +       __DEFINE_ASM_GPR_NUMS                                           \
> +"      .macro insn_r, opcode, func3, func7, rd, rs1, rs2\n"            \
> +"      .4byte  ((\\opcode << " __stringify(INSN_R_OPCODE_SHIFT) ") |"  \
> +"               (\\func3 << " __stringify(INSN_R_FUNC3_SHIFT) ") |"    \
> +"               (\\func7 << " __stringify(INSN_R_FUNC7_SHIFT) ") |"    \
> +"               (.L__gpr_num_\\rd << " __stringify(INSN_R_RD_SHIFT) ") |"    \
> +"               (.L__gpr_num_\\rs1 << " __stringify(INSN_R_RS1_SHIFT) ") |"  \
> +"               (.L__gpr_num_\\rs2 << " __stringify(INSN_R_RS2_SHIFT) "))\n" \
> +"      .endm\n"
> +
> +#define UNDEFINE_INSN_R                                                        \
> +"      .purgem insn_r\n"
> +
> +#define INSN_R(opcode, func3, func7, rd, rs1, rs2)                     \
> +       DEFINE_INSN_R                                                   \
> +       "insn_r " opcode ", " func3 ", " func7 ", " rd ", " rs1 ", " rs2 "\n" \
> +       UNDEFINE_INSN_R
> +
> +#endif
> +
> +#endif /* ! __ASSEMBLY__ */
> +
> +#define OPCODE(v)      __ASM_STR(v)
> +#define FUNC3(v)       __ASM_STR(v)
> +#define FUNC7(v)       __ASM_STR(v)
> +#define __REG(v)       __ASM_STR(x ## v)
> +#define RD(v)          __REG(v)
> +#define RS1(v)         __REG(v)
> +#define RS2(v)         __REG(v)
> +
> +#endif /* __ASM_INSN_DEF_H */
> --
> 2.37.1
>

Apart from new nit comments above, this looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup