linux-kernel - Re: [PATCH v2 5/9] LoongArch: Simplify the invtlb wrappers

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Message-ID: <bb4c5746bba9c96f083cbff0ced4185f88bef33a.camel@xry111.site>
Date:   Sun, 25 Jun 2023 02:55:01 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     WANG Xuerui <kernel@...0n.name>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Rui <wangrui@...ngson.cn>, loongarch@...ts.linux.dev,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, WANG Xuerui <git@...0n.name>
Subject: Re: [PATCH v2 5/9] LoongArch: Simplify the invtlb wrappers

On Sun, 2023-06-25 at 02:40 +0800, WANG Xuerui wrote:
> From: WANG Xuerui <git@...0n.name>
> 
> The invtlb instruction has been supported by upstream LoongArch
> toolchains from day one, so ditch the raw opcode trickery and just use
> plain inline asm for it.
> 
> While at it, also make the invtlb asm statements barriers, for proper
> modeling of the side effects.
> 
> The signature of the other more specific invtlb wrappers contain unused
> arguments right now, but these are not removed right away in order for
> the patch to be focused. In the meantime, assertions are added to ensure
> no accidental misuse happens before the refactor. (The more specific
> wrappers cannot re-use the generic invtlb wrapper, because the ISA
> manual says $zero shall be used in case a particular op does not take
> the respective argument: re-using the generic wrapper would mean losing
> control over the register usage.)
> 
> Signed-off-by: WANG Xuerui <git@...0n.name>
> ---
>  arch/loongarch/include/asm/tlb.h | 39 ++++++++++++++++----------------
>  1 file changed, 19 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/loongarch/include/asm/tlb.h b/arch/loongarch/include/asm/tlb.h
> index 0dc9ee2b05d2..15750900540c 100644
> --- a/arch/loongarch/include/asm/tlb.h
> +++ b/arch/loongarch/include/asm/tlb.h
> @@ -88,52 +88,51 @@ enum invtlb_ops {
>         INVTLB_GID_ADDR = 0x16,
>  };
>  
> -/*
> - * invtlb op info addr
> - * (0x1 << 26) | (0x24 << 20) | (0x13 << 15) |
> - * (addr << 10) | (info << 5) | op
> - */
>  static inline void invtlb(u32 op, u32 info, u64 addr)

Oh, technically these wrappers should be __always_inline, not only
inline because they don't work at all if not inlined.  Should we change
them to __always_inline in this patch by the way?

>  {
> +       BUILD_BUG_ON(!__builtin_constant_p(op));

Hmm, I guess it's redundant.  If op is not a compile-time constant, it
won't satisfy the "i" constraint then the compiler will complain anyway.

>         __asm__ __volatile__(
> -               "parse_r addr,%0\n\t"
> -               "parse_r info,%1\n\t"
> -               ".word ((0x6498000) | (addr << 10) | (info << 5) | %2)\n\t"
> -               :
> -               : "r"(addr), "r"(info), "i"(op)
> +               "invtlb %0, %1, %2\n\t"
>                 :
> +               : "i"(op), "r"(info), "r"(addr)
> +               : "memory"
>                 );
>  }

Likewise for other wrappers.

/* snip */

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University