linux-kernel - Re: [PATCH] LoongArch: Add unaligned access support

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Date:   Mon, 17 Oct 2022 08:16:53 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Xi Ruoyao <xry111@...111.site>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>, loongarch@...ts.linux.dev,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Add unaligned access support

Hi, Ruoyao,

On Sun, Oct 16, 2022 at 11:05 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> On Sun, 2022-10-16 at 21:34 +0800, Huacai Chen wrote:
>
> > Loongson-2 series (Loongson-2K500, Loongson-2K1000)
>
> "2K1000LA"? "2K1000" is puzzling because of a name conflict with the
> MIPS-based model.
Technically this is correct, both MIPS-based and LoongArch-based
Loongson-2K1000 have no hardware support.

>
> /* snip */
>
> > +static inline unsigned long read_fpr(unsigned int fd)
> > +{
> > +#define READ_FPR(fd, __value)          \
> > +{                                      \
>
> Unnecessary curly brace pair.
OK,thanks.

>
> > +       __asm__ __volatile__(           \
> > +       "movfr2gr.d\t%0, $f%1\n\t"      \
> > +       : "=r"(__value) : "i"(fd));     \
> > +}
>
> I'm not sure if this is a correct use of "i" constraint.  Maybe we
> should just concatenate the string?
OK, thanks.

Huacai
>
> "movfr2gr.d\t%0, $f" #fd "\n\t"
>
> > +
> > +       unsigned long __value;
> > +
> > +       switch (fd) {
>
> I don't like this "very long" switch statement, but it seems we have no
> way to make it better...
>
> > +       case 0:
> > +               READ_FPR(0, __value);
> > +               break;
> > +       case 1:
> > +               READ_FPR(1, __value);
> > +               break;
> > +       case 2:
> > +               READ_FPR(2, __value);
> > +               break;
>
> --
> Xi Ruoyao <xry111@...111.site>
> School of Aerospace Science and Technology, Xidian University