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SubjectRe: [PATCH 3/3] net: marvell: prestera: force good base mac
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On 3/11/24 14:51, Elad Nachman wrote:
> From: Elad Nachman <enachman@marvell.com>
>
> Since each switchport MAC address uses the switch base mac address
> and adds the physical port number to it,
> Force the last byte of the switch base mac address to be at
> least 128, so when adding to it, we will not wrap around the

to be at *most* 128

> previous (more significant) mac address byte, resulting in a
> warning message.
>
> Signed-off-by: Elad Nachman <enachman@marvell.com>
> ---
> drivers/net/ethernet/marvell/prestera/prestera_main.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/marvell/prestera/prestera_main.c b/drivers/net/ethernet/marvell/prestera/prestera_main.c
> index bcaa8ea27b49..e17b1a24fe18 100644
> --- a/drivers/net/ethernet/marvell/prestera/prestera_main.c
> +++ b/drivers/net/ethernet/marvell/prestera/prestera_main.c
> @@ -859,7 +859,9 @@ static int prestera_switch_set_base_mac_addr(struct prestera_switch *sw)
> if (sw->np)
> ret = of_get_mac_address(sw->np, sw->base_mac);
> if (!is_valid_ether_addr(sw->base_mac) || ret) {
> - eth_random_addr(sw->base_mac);
> + do {
> + eth_random_addr(sw->base_mac);
> + } while (sw->base_mac[5] > 0x80);

Instead of this loop, that uses 6 bytes of random data at each step,
I would just fix the last byte.

Either by calling get_random_u8() in a loop, or perhaps better, just
toggle of MSB unconditionally:
sw->base_mac[5] &= ~0x80; // or '&= 127'

what would change your condition in commit message to "to be at most
127", but I think that should be fine, granted simpler code.

> dev_info(prestera_dev(sw), "using random base mac address\n");
> }
>


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