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SubjectRe: [PATCH v10 1/3] ARM: uncompress: Add be32tocpu macro
Hallo Geert,

On Thu, 3 Dec 2020 at 13:19, Geert Uytterhoeven <geert+renesas@glider.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@glider.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@kernel.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
>

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