[PATCH 5/6] net: lwip: dhcp: Save DHCP siaddr field to tftpserverip env var

[Jonas Karlman]

The DHCP siaddr field contains the IP address of next server to use in
bootstrap. Typically this will be the IP address of a TFTP server or the
IP address of the DHCP server itself.

RFC 2131, 2. Protocol Summary, Page 10:

   DHCP clarifies the interpretation of the 'siaddr' field as the
   address of the server to use in the next step of the client's
   bootstrap process.  A DHCP server may return its own address in the
   'siaddr' field, if the server is prepared to supply the next
   bootstrap service (e.g., delivery of an operating system executable
   image).  A DHCP server always returns its own address in the 'server
   identifier' option.

Set the 'tftpserverip' env variable when the siaddr field contains an
IP address that is different compared to the DHCP server IP address.

Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
---
 net/lwip/dhcp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/lwip/dhcp.c b/net/lwip/dhcp.c
index 4cd4184c42bb..acdf601d7eb5 100644
--- a/net/lwip/dhcp.c
+++ b/net/lwip/dhcp.c
@@ -101,6 +101,9 @@ static int dhcp_loop(struct udevice *udev)
 	env_set("serverip", ip4addr_ntoa(&dhcp->server_ip_addr));
 	if (!ip4_addr_isany(&dhcp->offered_gw_addr))
 		env_set(gwstr, ip4addr_ntoa(&dhcp->offered_gw_addr));
+	if (!ip4_addr_isany(&dhcp->offered_si_addr) &&
+	    !ip4_addr_eq(&dhcp->offered_si_addr, &dhcp->server_ip_addr))
+		env_set("tftpserverip", ip4addr_ntoa(&dhcp->offered_si_addr));
 
 #ifdef CONFIG_PROT_DNS_LWIP
 	env_set("dnsip", ip4addr_ntoa(dns_getserver(0)));
-- 
2.52.0