linux-kernel - Re: [PATCH v10 1/3] ARM: uncompress: Add be32tocpu macro

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Message-ID: <CAMj1kXEKdRGQXFh9qMgrWcZnoW5s8Bj5TaKqStU=w1qJ-Nu9zA@mail.gmail.com>
Date:   Thu, 3 Dec 2020 13:49:49 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Miao <eric.miao@...dia.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Lukasz Stelmach <l.stelmach@...sung.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Chris Brandt <chris.brandt@...esas.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 1/3] ARM: uncompress: Add be32tocpu macro

Hallo Geert,

On Thu, 3 Dec 2020 at 13:19, Geert Uytterhoeven <geert+renesas@...der.be> wrote:
>
> DTB stores all values as 32-bit big-endian integers.
> Add a macro to convert such values to native CPU endianness, to reduce
> duplication.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> v10:
>   - New.
> ---
>  arch/arm/boot/compressed/head.S | 26 ++++++++++++--------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 835ce64f1674c9a2..aabdc544c03aafdc 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -165,6 +165,16 @@
>                 orr     \res, \res, \tmp1, lsl #24
>                 .endm
>
> +               .macro  be32tocpu, val, tmp
> +#ifndef __ARMEB__
> +               /* convert to little endian */
> +               eor     \tmp, \val, \val, ror #16
> +               bic     \tmp, \tmp, #0x00ff0000
> +               mov     \val, \val, ror #8
> +               eor     \val, \val, \tmp, lsr #8
> +#endif
> +               .endm
> +

Thanks for cleaning this up.

This patch is fine as is.

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>

However, I would like to note that, since we are touching this code,
we might do it properly. (Given the v10, feel free to ignore or defer
to a later time)

- put this into asm/assembler.h so other .S files can use it
- use rev instructions when supported
- factor out the difference between xx_to cpu and bswap

I.e.,

.macro bswap32, val, tmp
.if  __LINUX_ARM_ARCH__ >= 6
rev \val, \val
.else
eor     \tmp, \val, \val, ror #16
bic     \tmp, \tmp, #0x00ff0000
mov     \val, \val, ror #8
eor     \val, \val, \tmp, lsr #8
.endif
.endm

.macro  be32tocpu, val, tmp
#ifndef __ARMEB__
bswap32 \val, \tmp
#endif
.endm

.macro  le32tocpu, val, tmp
#ifdef __ARMEB__
bswap32 \val, \tmp
#endif
.endm

This would allow us to reuse this macro in
arch/arm/crypto/aes-cipher-core.S, and replace the __rev macro it
defines.


>                 .section ".start", "ax"
>  /*
>   * sort out different calling conventions
> @@ -345,13 +355,7 @@ restart:   adr     r0, LC1
>
>                 /* Get the initial DTB size */
>                 ldr     r5, [r6, #4]
> -#ifndef __ARMEB__
> -               /* convert to little endian */
> -               eor     r1, r5, r5, ror #16
> -               bic     r1, r1, #0x00ff0000
> -               mov     r5, r5, ror #8
> -               eor     r5, r5, r1, lsr #8
> -#endif
> +               be32tocpu r5, r1
>                 dbgadtb r6, r5
>                 /* 50% DTB growth should be good enough */
>                 add     r5, r5, r5, lsr #1
> @@ -403,13 +407,7 @@ restart:   adr     r0, LC1
>
>                 /* Get the current DTB size */
>                 ldr     r5, [r6, #4]
> -#ifndef __ARMEB__
> -               /* convert r5 (dtb size) to little endian */
> -               eor     r1, r5, r5, ror #16
> -               bic     r1, r1, #0x00ff0000
> -               mov     r5, r5, ror #8
> -               eor     r5, r5, r1, lsr #8
> -#endif
> +               be32tocpu r5, r1
>
>                 /* preserve 64-bit alignment */
>                 add     r5, r5, #7
> --
> 2.25.1
>