diff mbox series

[2/3] net: ftmac100: report the correct maximum MTU of 1500

Message ID 20221028183220.155948-2-saproj@gmail.com (mailing list archive)
State Accepted
Commit 30f837b7b92394599ddc366ff4cf8b77d070d4f4
Delegated to: Netdev Maintainers
Headers show
Series [1/3] net: ftmac100: prepare data path for receiving single segment packets > 1514 | expand

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netdev/cover_letter warning Series does not have a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers success CCed 8 of 8 maintainers
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 15 lines checked
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netdev/source_inline success Was 0 now: 0

Commit Message

Sergei Antonov Oct. 28, 2022, 6:32 p.m. UTC 
From: Vladimir Oltean <vladimir.oltean@nxp.com>

The driver uses the MAX_PKT_SIZE (1518) for both MTU reporting and for
TX. However, the 2 places do not measure the same thing.

On TX, skb->len measures the entire L2 packet length (without FCS, which
software does not possess). So the comparison against 1518 there is
correct.

What is not correct is the reporting of dev->max_mtu as 1518. Since MTU
measures L2 *payload* length (excluding L2 overhead) and not total L2
packet length, it means that the correct max_mtu supported by this
device is the standard 1500. Anything higher than that will be dropped
on RX currently.

To fix this, subtract VLAN_ETH_HLEN from MAX_PKT_SIZE when reporting the
max_mtu, since that is the difference between L2 payload length and
total L2 length as seen by software.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Sergei Antonov <saproj@gmail.com>
---
 drivers/net/ethernet/faraday/ftmac100.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/drivers/net/ethernet/faraday/ftmac100.c b/drivers/net/ethernet/faraday/ftmac100.c
index 8013f85fc148..7c571b4515a9 100644
--- a/drivers/net/ethernet/faraday/ftmac100.c
+++ b/drivers/net/ethernet/faraday/ftmac100.c
@@ -11,6 +11,7 @@ 
 #include <linux/dma-mapping.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
+#include <linux/if_vlan.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -1070,7 +1071,7 @@  static int ftmac100_probe(struct platform_device *pdev)
 	SET_NETDEV_DEV(netdev, &pdev->dev);
 	netdev->ethtool_ops = &ftmac100_ethtool_ops;
 	netdev->netdev_ops = &ftmac100_netdev_ops;
-	netdev->max_mtu = MAX_PKT_SIZE;
+	netdev->max_mtu = MAX_PKT_SIZE - VLAN_ETH_HLEN;
 
 	err = platform_get_ethdev_address(&pdev->dev, netdev);
 	if (err == -EPROBE_DEFER)