The datasheets for all SoCs using the GbEth IP specify a maximum
transmission frame size of 1.5 kByte. I've confirmed through internal
discussions that support for 1522 byte frames has been validated, which
allows us to support the default MTU of 1500 bytes after reserving space
for the Ethernet header, frame checksums and an optional VLAN tag.

Fixes: 2e95e08ac009 ("ravb: Add rx_max_buf_size to struct ravb_hw_info")
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
---
 drivers/net/ethernet/renesas/ravb.h      | 1 +
 drivers/net/ethernet/renesas/ravb_main.c | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
index 9893c91af105..a7de5cf6b317 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -1052,6 +1052,7 @@ struct ravb_hw_info {
 	netdev_features_t net_features;
 	int stats_len;
 	u32 tccr_mask;
+	u32 tx_max_frame_size;
 	u32 rx_max_frame_size;
 	u32 rx_buffer_size;
 	u32 rx_desc_size;
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index c7ec23688d56..e73cdba58516 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2674,6 +2674,7 @@ static const struct ravb_hw_info ravb_gen2_hw_info = {
 	.net_features = NETIF_F_RXCSUM,
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
 	.tccr_mask = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
+	.tx_max_frame_size = SZ_2K,
 	.rx_max_frame_size = SZ_2K,
 	.rx_buffer_size = SZ_2K +
 			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
@@ -2696,6 +2697,7 @@ static const struct ravb_hw_info ravb_gen3_hw_info = {
 	.net_features = NETIF_F_RXCSUM,
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
 	.tccr_mask = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
+	.tx_max_frame_size = SZ_2K,
 	.rx_max_frame_size = SZ_2K,
 	.rx_buffer_size = SZ_2K +
 			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
@@ -2721,6 +2723,7 @@ static const struct ravb_hw_info ravb_gen4_hw_info = {
 	.net_features = NETIF_F_RXCSUM,
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
 	.tccr_mask = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
+	.tx_max_frame_size = SZ_2K,
 	.rx_max_frame_size = SZ_2K,
 	.rx_buffer_size = SZ_2K +
 			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
@@ -2770,6 +2773,7 @@ static const struct ravb_hw_info gbeth_hw_info = {
 	.net_features = NETIF_F_RXCSUM | NETIF_F_HW_CSUM,
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats_gbeth),
 	.tccr_mask = TCCR_TSRQ0,
+	.tx_max_frame_size = 1522,
 	.rx_max_frame_size = SZ_8K,
 	.rx_buffer_size = SZ_2K,
 	.rx_desc_size = sizeof(struct ravb_rx_desc),
@@ -2981,7 +2985,7 @@ static int ravb_probe(struct platform_device *pdev)
 	priv->avb_link_active_low =
 		of_property_read_bool(np, "renesas,ether-link-active-low");
 
-	ndev->max_mtu = info->rx_max_frame_size -
+	ndev->max_mtu = info->tx_max_frame_size -
 		(ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
 	ndev->min_mtu = ETH_MIN_MTU;
 
-- 
2.43.0

On Wed, Sep 18, 2024 at 09:18:38AM +0100, Paul Barker wrote:
> The datasheets for all SoCs using the GbEth IP specify a maximum
> transmission frame size of 1.5 kByte. I've confirmed through internal
> discussions that support for 1522 byte frames has been validated, which
> allows us to support the default MTU of 1500 bytes after reserving space
> for the Ethernet header, frame checksums and an optional VLAN tag.
> 
> Fixes: 2e95e08ac009 ("ravb: Add rx_max_buf_size to struct ravb_hw_info")
> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>

Reviewed-by: Simon Horman <horms@kernel.org>