[PATCH net-next] net/ncsi: allow to customize BMC MAC Address offset

[Jakub Kicinski]

On Tue, 6 Aug 2019 17:21:18 -0700, Tao Ren wrote:
> Currently BMC's MAC address is calculated by adding 1 to NCSI NIC's base
> MAC address when CONFIG_NCSI_OEM_CMD_GET_MAC option is enabled. The logic
> doesn't work for platforms with different BMC MAC offset: for example,
> Facebook Yamp BMC's MAC address is calculated by adding 2 to NIC's base
> MAC address ("BaseMAC + 1" is reserved for Host use).
> 
> This patch adds NET_NCSI_MC_MAC_OFFSET config option to customize offset
> between NIC's Base MAC address and BMC's MAC address. Its default value is
> set to 1 to avoid breaking existing users.
> 
> Signed-off-by: Tao Ren <taoren at fb.com>

Maybe someone more knowledgeable like Andrew has an opinion here, 
but to me it seems a bit strange to encode what seems to be platfrom
information in the kernel config :(

> diff --git a/net/ncsi/Kconfig b/net/ncsi/Kconfig
> index 2f1e5756c03a..be8efe1ed99e 100644
> --- a/net/ncsi/Kconfig
> +++ b/net/ncsi/Kconfig
> @@ -17,3 +17,11 @@ config NCSI_OEM_CMD_GET_MAC
>  	---help---
>  	  This allows to get MAC address from NCSI firmware and set them back to
>  		controller.
> +config NET_NCSI_MC_MAC_OFFSET
> +	int
> +	prompt "Offset of Management Controller's MAC Address"
> +	depends on NCSI_OEM_CMD_GET_MAC
> +	default 1
> +	help
> +	  This defines the offset between Network Controller's (base) MAC
> +	  address and Management Controller's MAC address.
> diff --git a/net/ncsi/ncsi-rsp.c b/net/ncsi/ncsi-rsp.c
> index 7581bf919885..24a791f9ebf5 100644
> --- a/net/ncsi/ncsi-rsp.c
> +++ b/net/ncsi/ncsi-rsp.c
> @@ -656,6 +656,11 @@ static int ncsi_rsp_handler_oem_bcm_gma(struct ncsi_request *nr)
>  	struct ncsi_rsp_oem_pkt *rsp;
>  	struct sockaddr saddr;
>  	int ret = 0;
> +#ifdef CONFIG_NET_NCSI_MC_MAC_OFFSET
> +	int mac_offset = CONFIG_NET_NCSI_MC_MAC_OFFSET;
> +#else
> +	int mac_offset = 1;
> +#endif
>  
>  	/* Get the response header */
>  	rsp = (struct ncsi_rsp_oem_pkt *)skb_network_header(nr->rsp);
> @@ -663,8 +668,14 @@ static int ncsi_rsp_handler_oem_bcm_gma(struct ncsi_request *nr)
>  	saddr.sa_family = ndev->type;
>  	ndev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
>  	memcpy(saddr.sa_data, &rsp->data[BCM_MAC_ADDR_OFFSET], ETH_ALEN);
> -	/* Increase mac address by 1 for BMC's address */
> -	eth_addr_inc((u8 *)saddr.sa_data);
> +
> +	/* Management Controller's MAC address is calculated by adding
> +	 * the offset to Network Controller's (base) MAC address.
> +	 * Note: negative offset is "ignored", and BMC will use the Base
> +	 * MAC address in this case.
> +	 */
> +	while (mac_offset-- > 0)
> +		eth_addr_inc((u8 *)saddr.sa_data);
>  	if (!is_valid_ether_addr((const u8 *)saddr.sa_data))
>  		return -ENXIO;
>