2023-11-05 20:57:39

by Linus Walleij

Subject: [PATCH net v2 1/4] net: ethernet: cortina: Fix MTU max setting

The RX max frame size is over 10000 for the Gemini ethernet,
but the TX max frame size is actually just 2047 (0x7ff after
checking the datasheet). Reflect this in what we offer to Linux,
cap the MTU at the TX max frame minus ethernet headers.

Use the BIT() macro for related bit flags so these TX settings
are consistent.

Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
Signed-off-by: Linus Walleij <[email protected]>
---
drivers/net/ethernet/cortina/gemini.c | 7 ++++---
drivers/net/ethernet/cortina/gemini.h | 2 +-
2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index 5423fe26b4ef..ed9701f8ad9a 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -2464,11 +2464,12 @@ static int gemini_ethernet_port_probe(struct platform_device *pdev)

netdev->hw_features = GMAC_OFFLOAD_FEATURES;
netdev->features |= GMAC_OFFLOAD_FEATURES | NETIF_F_GRO;
- /* We can handle jumbo frames up to 10236 bytes so, let's accept
- * payloads of 10236 bytes minus VLAN and ethernet header
+ /* We can receive jumbo frames up to 10236 bytes but only
+ * transmit 2047 bytes so, let's accept payloads of 2047
+ * bytes minus VLAN and ethernet header
*/
netdev->min_mtu = ETH_MIN_MTU;
- netdev->max_mtu = 10236 - VLAN_ETH_HLEN;
+ netdev->max_mtu = MTU_SIZE_BIT_MASK - VLAN_ETH_HLEN;

port->freeq_refill = 0;
netif_napi_add(netdev, &port->napi, gmac_napi_poll);
diff --git a/drivers/net/ethernet/cortina/gemini.h b/drivers/net/ethernet/cortina/gemini.h
index 9fdf77d5eb37..201b4efe2937 100644
--- a/drivers/net/ethernet/cortina/gemini.h
+++ b/drivers/net/ethernet/cortina/gemini.h
@@ -502,7 +502,7 @@ union gmac_txdesc_3 {
#define SOF_BIT 0x80000000
#define EOF_BIT 0x40000000
#define EOFIE_BIT BIT(29)
-#define MTU_SIZE_BIT_MASK 0x1fff
+#define MTU_SIZE_BIT_MASK 0x7ff /* Max MTU 2047 bytes */

/* GMAC Tx Descriptor */
struct gmac_txdesc {

--
2.34.1

2023-11-05 23:39:39

by Andrew Lunn

Subject: Re: [PATCH net v2 1/4] net: ethernet: cortina: Fix MTU max setting

On Sun, Nov 05, 2023 at 09:57:23PM +0100, Linus Walleij wrote:
> The RX max frame size is over 10000 for the Gemini ethernet,
> but the TX max frame size is actually just 2047 (0x7ff after
> checking the datasheet). Reflect this in what we offer to Linux,
> cap the MTU at the TX max frame minus ethernet headers.
>
> Use the BIT() macro for related bit flags so these TX settings
> are consistent.
>
> Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
> Signed-off-by: Linus Walleij <[email protected]>

Reviewed-by: Andrew Lunn <[email protected]>

Andrew