[PATCH net-next v3] net: airoha_eth: increase max MTU to 9220 for DSA jumbo frames

[Sayantan Nandy]

The industry standard jumbo frame MTU is 9216 bytes. When using the DSA
subsystem, a 4-byte tag is added to each Ethernet frame.

Increase AIROHA_MAX_MTU to 9220 bytes (9216 + 4) so that users can set a
standard 9216-byte MTU on DSA ports.

The underlying hardware supports significantly larger frame sizes
(approximately 16K). However, the maximum MTU is limited to 9220 bytes
for now, as this is sufficient to support standard jumbo frames and does
not incur additional memory allocation overhead.


Signed-off-by: Sayantan Nandy <sayantann11 at gmail.com>
---
v3:
- Document that hardware supports larger MTU (~16K), but limit to 9220 for now
- Target net-next (netdev/main) as this is a feature enhancement
- No functional changes

v2:
- Clarified commit message regarding DSA tag overhead

 drivers/net/ethernet/airoha/airoha_eth.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/drivers/net/ethernet/airoha/airoha_eth.h b/drivers/net/ethernet/airoha/airoha_eth.h
index fbbc58133364..20e602d61e61 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.h
+++ b/drivers/net/ethernet/airoha/airoha_eth.h
@@ -21,7 +21,7 @@
 #define AIROHA_MAX_NUM_IRQ_BANKS	4
 #define AIROHA_MAX_DSA_PORTS		7
 #define AIROHA_MAX_NUM_RSTS		3
-#define AIROHA_MAX_MTU			9216
+#define AIROHA_MAX_MTU			9220
 #define AIROHA_MAX_PACKET_SIZE		2048
 #define AIROHA_NUM_QOS_CHANNELS		4
 #define AIROHA_NUM_QOS_QUEUES		8
-- 
2.43.0