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 <tao...@fb.com>
---
 net/ncsi/Kconfig    |  8 ++++++++
 net/ncsi/ncsi-rsp.c | 15 +++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

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;
 
-- 
2.17.1

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