[PATCH v2] net: lwip: Fix PBUF_POOL_BUFSIZE when PROT_TCP_LWIP is disabled

[Jonas Karlman]

The PBUF_POOL_BUFSIZE ends up being only 592 bytes, instead of 1514,
when PROT_TCP_LWIP Kconfig option is disabled. This results in a full
Ethernet frame requiring three PBUFs instead of just one.

This happens because the PBUF_POOL_BUFSIZE constant depends on the value
of a TCP_MSS constant, something that defaults to 536 when PROT_TCP_LWIP
is disabled.

  PBUF_POOL_BUFSIZE = LWIP_MEM_ALIGN_SIZE(TCP_MSS + 40 + PBUF_LINK_HLEN)

Ensure that a full Ethernet frame fits inside a single PBUF by moving
the define of TCP_MSS outside the PROT_TCP_LWIP ifdef block.

Fixes: 1c41a7afaa15 ("net: lwip: build lwIP")
Acked-by: Jerome Forissier <jerome.forissier at arm.com>
Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
---
Changes in v2:
- Add comment
- Collect a-b tag
---
 lib/lwip/u-boot/lwipopts.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/lwip/u-boot/lwipopts.h b/lib/lwip/u-boot/lwipopts.h
index e8a2c9d7a0a6..1550870fa866 100644
--- a/lib/lwip/u-boot/lwipopts.h
+++ b/lib/lwip/u-boot/lwipopts.h
@@ -121,9 +121,13 @@
 #define LWIP_UDP                        0
 #endif
 
+/*
+ * PBUF_POOL_BUFSIZE is derived from TCP_MSS even when
+ * CONFIG_PROT_TCP_LWIP is not defined
+ */
+#define TCP_MSS                         1460
 #if defined(CONFIG_PROT_TCP_LWIP)
 #define LWIP_TCP                        1
-#define TCP_MSS                         1460
 #define TCP_WND                         CONFIG_LWIP_TCP_WND
 #define LWIP_WND_SCALE                  1
 #define TCP_RCV_SCALE                   0x7
-- 
2.53.0