Re: [PATCH v2 2/2] arm: mach-snapdrgon: misc: Simplify msm_generate_mac_addr()

[Ramon Fried <rfried.dev@gmail.com>]

On Tue, Aug 3, 2021 at 1:12 PM Stephan Gerhold <stephan@gerhold.net> wrote:
>
> The logic in msm_generate_mac_addr() was originally taken from the LK
> bootloader where the serial number is a string and must be parsed first.
> However, in U-Boot msm_board_serial() returns an u32 and
> msm_generate_mac_addr() has quite complicated code that will first
> print it as a hex string and then immediately parse it again.
>
> What this function actually does at the end is to put the serial number
> encoded as big endian (the order used for the hex string) into the u8 *mac.
> Use put_unaligned_be32() to do that with bit shifts instead of going
> through the string format.
>
> This should be slightly more efficient and cleaner but does not result
> in any functional difference.
>
> Cc: Ramon Fried <rfried.dev@gmail.com>
> Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
> ---
>
> Changes in v2:
>   - Rebase on u-boot/master to fix conflict with recent changes
>   - Add comment to clarify what put_unaligned_be32() does here
>
>  arch/arm/mach-snapdragon/misc.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm/mach-snapdragon/misc.c b/arch/arm/mach-snapdragon/misc.c
> index fbd5f4d051..7d452f4529 100644
> --- a/arch/arm/mach-snapdragon/misc.c
> +++ b/arch/arm/mach-snapdragon/misc.c
> @@ -9,6 +9,7 @@
>  #include <common.h>
>  #include <mmc.h>
>  #include <asm/arch/misc.h>
> +#include <asm/unaligned.h>
>
>  /* UNSTUFF_BITS macro taken from Linux Kernel: drivers/mmc/core/sd.c */
>  #define UNSTUFF_BITS(resp, start, size) \
> @@ -41,16 +42,14 @@ u32 msm_board_serial(void)
>
>  void msm_generate_mac_addr(u8 *mac)
>  {
> -       int i;
> -       char sn[9];
> -
> -       snprintf(sn, 9, "%08x", msm_board_serial());
> -
> -       /* fill in the mac with serialno, use locally adminstrated pool */
> +       /* use locally adminstrated pool */
>         mac[0] = 0x02;
> -       mac[1] = 00;
> -       for (i = 3; i >= 0; i--) {
> -               mac[i + 2] = hextoul(&sn[2 * i], NULL);
> -               sn[2 * i] = 0;
> -       }
> +       mac[1] = 0x00;
> +
> +       /*
> +        * Put the 32-bit serial number in the last 32-bit of the MAC address.
> +        * Use big endian order so it is consistent with the serial number
> +        * written as a hexadecimal string, e.g. 0x1234abcd -> 02:00:12:34:ab:cd
> +        */
> +       put_unaligned_be32(msm_board_serial(), &mac[2]);
>  }
> --
> 2.32.0
>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>