[PATCH net v3 0/4] Fix large frames in the Gemini ethernet driver

[PATCH net v3 0/4] Fix large frames in the Gemini ethernet driver

[Linus Walleij]

This is the result of a bug hunt for a problem with the
RTL8366RB DSA switch leading me wrong all over the place.

I am indebted to Vladimir Oltean who as usual pointed
out where the real problem was, many thanks!

Tryig to actually use big ("jumbo") frames on this
hardware uncovered the real bugs. Then I tested it on
the DSA switch and it indeed fixes the issue.

To make sure it also works fine with big frames on
non-DSA devices I also copied a large video file over
scp to a device with maximum frame size, the data
was transported in large TCP packets ending up in
0x7ff sized frames using software checksumming at
~2.0 MB/s.

If I set down the MTU to the standard 1500 bytes so
that hardware checksumming is used, the scp transfer
of the same file was slightly lower, ~1.8-1.9 MB/s.

Despite this not being the best test it shows that
we can now stress the hardware with large frames
and that software checksum works fine.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Changes in v3:
- Do not reimplement the existing oversize check (sigh what is
  wrong with me). Drop that patch.
- Drop the gmac_fix_features() since we are better off falling
  back to software checksums dynamically per-frame.
- Add a new patch to bypass the checksumming engine if we are not
  handling TCP or UDP.
- Link to v2: https://lore.kernel.org/r/20231105-gemini-largeframe-fix-v2-0-cd3a5aa6c496@linaro.org

Changes in v2:
- Don't check for oversized MTU request: the framework makes sure it doesn't
  happen.
- Drop unrelated BIT() macro cleanups (I might send these later for net-next)
- Use a special error code if the skbuff is too big and fail gracefully
  is this happens.
- Do proper checksum of the frame using a software fallback when the frame
  is too long for hardware checksumming.
- Link to v1: https://lore.kernel.org/r/20231104-gemini-largeframe-fix-v1-0-9c5513f22f33@linaro.org

---
Linus Walleij (4):
      net: ethernet: cortina: Fix MTU max setting
      net: ethernet: cortina: Fix max RX frame define
      net: ethernet: cortina: Handle large frames
      net: ethernet: cortina: Checksum only TCP and UDP

 drivers/net/ethernet/cortina/gemini.c | 66 +++++++++++++++++++++++------------
 drivers/net/ethernet/cortina/gemini.h |  4 +--
 2 files changed, 45 insertions(+), 25 deletions(-)
---
base-commit: e85fd73c7d9630d392f451fcf69a457c8e3f21dd
change-id: 20231104-gemini-largeframe-fix-c143d2c781b5

Best regards,
-- 
Linus Walleij <linus.walleij@linaro.org>

[PATCH net v3 1/4] net: ethernet: cortina: Fix MTU max setting

[Linus Walleij]

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")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 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

[PATCH net v3 2/4] net: ethernet: cortina: Fix max RX frame define

[Linus Walleij]

Enumerator 3 is 1548 bytes according to the datasheet.
Not 1542.

Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/net/ethernet/cortina/gemini.c | 4 ++--
 drivers/net/ethernet/cortina/gemini.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index ed9701f8ad9a..b21a94b4ab5c 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -432,8 +432,8 @@ static const struct gmac_max_framelen gmac_maxlens[] = {
 		.val = CONFIG0_MAXLEN_1536,
 	},
 	{
-		.max_l3_len = 1542,
-		.val = CONFIG0_MAXLEN_1542,
+		.max_l3_len = 1548,
+		.val = CONFIG0_MAXLEN_1548,
 	},
 	{
 		.max_l3_len = 9212,
diff --git a/drivers/net/ethernet/cortina/gemini.h b/drivers/net/ethernet/cortina/gemini.h
index 201b4efe2937..24bb989981f2 100644
--- a/drivers/net/ethernet/cortina/gemini.h
+++ b/drivers/net/ethernet/cortina/gemini.h
@@ -787,7 +787,7 @@ union gmac_config0 {
 #define  CONFIG0_MAXLEN_1536	0
 #define  CONFIG0_MAXLEN_1518	1
 #define  CONFIG0_MAXLEN_1522	2
-#define  CONFIG0_MAXLEN_1542	3
+#define  CONFIG0_MAXLEN_1548	3
 #define  CONFIG0_MAXLEN_9k	4	/* 9212 */
 #define  CONFIG0_MAXLEN_10k	5	/* 10236 */
 #define  CONFIG0_MAXLEN_1518__6	6

-- 
2.34.1

[PATCH net v3 3/4] net: ethernet: cortina: Handle large frames

[Linus Walleij]

The Gemini ethernet controller provides hardware checksumming
for frames up to 1514 bytes including ethernet headers but not
FCS.

If we start sending bigger frames (after first bumping up the MTU
on both interfaces sending and receiveing the frames), truncated
packets start to appear on the target such as in this tcpdump
resulting from ping -s 1474:

23:34:17.241983 14:d6:4d:a8:3c:4f (oui Unknown) > bc:ae:c5:6b:a8:3d (oui Unknown),
ethertype IPv4 (0x0800), length 1514: truncated-ip - 2 bytes missing!
(tos 0x0, ttl 64, id 32653, offset 0, flags [DF], proto ICMP (1), length 1502)
OpenWrt.lan > Fecusia: ICMP echo request, id 1672, seq 50, length 1482

If we bypass the hardware checksumming and provide a software
fallback, everything starts working fine up to the max TX MTU
of 2047 bytes, for example ping -s2000 192.168.1.2:

00:44:29.587598 bc:ae:c5:6b:a8:3d (oui Unknown) > 14:d6:4d:a8:3c:4f (oui Unknown),
ethertype IPv4 (0x0800), length 2042:
(tos 0x0, ttl 64, id 51828, offset 0, flags [none], proto ICMP (1), length 2028)
Fecusia > OpenWrt.lan: ICMP echo reply, id 1683, seq 4, length 2008

The bit enabling to bypass hardware checksum (or any of the
"TSS" bits) are undocumented in the hardware reference manual.
The entire hardware checksum unit appears undocumented. The
conclusion that we need to use the "bypass" bit was found by
trial-and-error.

Since no hardware checksum will happen, we slot in a software
checksum fallback.

Check for the condition where we need to compute checksum on the
skb with either hardware or software using == CHECKSUM_PARTIAL instead
of != CHECKSUM_NONE which is an incomplete check according to
<linux/skbuff.h>.

We delete the code disabling the hardware checksum for large
MTU:s: this is suboptimal because it will disable hardware
checksumming also on small packets which the checksumming
engine can handle just fine, which is a waste of resources.

On the D-Link DIR-685 router this fixes a bug on the conduit
interface to the RTL8366RB DSA switch: as the switch needs to add
space for its tag it increases the MTU on the conduit interface
to 1504 and that means that when the router sends packages
of 1500 bytes these get an extra 4 bytes of DSA tag and the
transfer fails because of the erroneous hardware checksumming,
affecting such basic functionality as the LuCI web interface.

Suggested-by: Vladimir Oltean <olteanv@gmail.com>
Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/net/ethernet/cortina/gemini.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index b21a94b4ab5c..78287cfcbf63 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -1145,6 +1145,7 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 	dma_addr_t mapping;
 	unsigned short mtu;
 	void *buffer;
+	int ret;
 
 	mtu  = ETH_HLEN;
 	mtu += netdev->mtu;
@@ -1159,9 +1160,30 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 		word3 |= mtu;
 	}
 
-	if (skb->ip_summed != CHECKSUM_NONE) {
+	if (skb->len >= ETH_FRAME_LEN) {
+		/* Hardware offloaded checksumming isn't working on frames
+		 * bigger than 1514 bytes. A hypothesis about this is that the
+		 * checksum buffer is only 1518 bytes, so when the frames get
+		 * bigger they get truncated, or the last few bytes get
+		 * overwritten by the FCS.
+		 *
+		 * Just use software checksumming and bypass on bigger frames.
+		 */
+		if (skb->ip_summed == CHECKSUM_PARTIAL) {
+			ret = skb_checksum_help(skb);
+			if (ret)
+				return ret;
+		}
+		word1 |= TSS_BYPASS_BIT;
+	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
 		int tcp = 0;
 
+		/* We do not switch off the checksumming on non TCP/UDP
+		 * frames: as is shown from tests, the checksumming engine
+		 * is smart enough to see that a frame is not actually TCP
+		 * or UDP and then just pass it through without any changes
+		 * to the frame.
+		 */
 		if (skb->protocol == htons(ETH_P_IP)) {
 			word1 |= TSS_IP_CHKSUM_BIT;
 			tcp = ip_hdr(skb)->protocol == IPPROTO_TCP;
@@ -1978,15 +2000,6 @@ static int gmac_change_mtu(struct net_device *netdev, int new_mtu)
 	return 0;
 }
 
-static netdev_features_t gmac_fix_features(struct net_device *netdev,
-					   netdev_features_t features)
-{
-	if (netdev->mtu + ETH_HLEN + VLAN_HLEN > MTU_SIZE_BIT_MASK)
-		features &= ~GMAC_OFFLOAD_FEATURES;
-
-	return features;
-}
-
 static int gmac_set_features(struct net_device *netdev,
 			     netdev_features_t features)
 {
@@ -2212,7 +2225,6 @@ static const struct net_device_ops gmac_351x_ops = {
 	.ndo_set_mac_address	= gmac_set_mac_address,
 	.ndo_get_stats64	= gmac_get_stats64,
 	.ndo_change_mtu		= gmac_change_mtu,
-	.ndo_fix_features	= gmac_fix_features,
 	.ndo_set_features	= gmac_set_features,
 };
 

-- 
2.34.1

[PATCH net v3 4/4] net: ethernet: cortina: Checksum only TCP and UDP

[Linus Walleij]

It is a bit odd that frames that are neither TCP or UDP
(such as ICMP or ARP) are still sent to the checksumming
engine, where they are clearly just ignored.

Rewrite the logic slightly so that we first check if the
frame is TCP or UDP, in that case bypass the checksum
engine.

Reported-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/net/ethernet/cortina/gemini.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index 78287cfcbf63..1bf07505653b 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -1144,6 +1144,7 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 	skb_frag_t *skb_frag;
 	dma_addr_t mapping;
 	unsigned short mtu;
+	bool tcp, udp;
 	void *buffer;
 	int ret;
 
@@ -1160,7 +1161,18 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 		word3 |= mtu;
 	}
 
-	if (skb->len >= ETH_FRAME_LEN) {
+	/* Check if the protocol is TCP or UDP */
+	tcp = false;
+	udp = false;
+	if (skb->protocol == htons(ETH_P_IP)) {
+		tcp = ip_hdr(skb)->protocol == IPPROTO_TCP;
+		udp = ip_hdr(skb)->protocol == IPPROTO_UDP;
+	} else { /* IPv6 */
+		tcp = ipv6_hdr(skb)->nexthdr == IPPROTO_TCP;
+		udp = ipv6_hdr(skb)->nexthdr == IPPROTO_UDP;
+	}
+
+	if (skb->len >= ETH_FRAME_LEN || (!tcp && !udp)) {
 		/* Hardware offloaded checksumming isn't working on frames
 		 * bigger than 1514 bytes. A hypothesis about this is that the
 		 * checksum buffer is only 1518 bytes, so when the frames get
@@ -1168,6 +1180,9 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 		 * overwritten by the FCS.
 		 *
 		 * Just use software checksumming and bypass on bigger frames.
+		 *
+		 * Bypass the checksumming engine for any protocols that are
+		 * not TCP or UDP.
 		 */
 		if (skb->ip_summed == CHECKSUM_PARTIAL) {
 			ret = skb_checksum_help(skb);
@@ -1176,22 +1191,14 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
 		}
 		word1 |= TSS_BYPASS_BIT;
 	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
-		int tcp = 0;
-
-		/* We do not switch off the checksumming on non TCP/UDP
-		 * frames: as is shown from tests, the checksumming engine
-		 * is smart enough to see that a frame is not actually TCP
-		 * or UDP and then just pass it through without any changes
-		 * to the frame.
+		/* If we get here we are dealing with a TCP or UDP frame
+		 * which is small enough to be processed by the checkumming
+		 * engine.
 		 */
-		if (skb->protocol == htons(ETH_P_IP)) {
+		if (skb->protocol == htons(ETH_P_IP))
 			word1 |= TSS_IP_CHKSUM_BIT;
-			tcp = ip_hdr(skb)->protocol == IPPROTO_TCP;
-		} else { /* IPv6 */
+		else
 			word1 |= TSS_IPV6_ENABLE_BIT;
-			tcp = ipv6_hdr(skb)->nexthdr == IPPROTO_TCP;
-		}
-
 		word1 |= tcp ? TSS_TCP_CHKSUM_BIT : TSS_UDP_CHKSUM_BIT;
 	}
 

-- 
2.34.1

Re: [PATCH net v3 1/4] net: ethernet: cortina: Fix MTU max setting

[Vladimir Oltean]

On Tue, Nov 07, 2023 at 10:54:26AM +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.

What does this second paragraph intend to say? The patch doesn't use the
BIT() macro.

Re: [PATCH net v3 1/4] net: ethernet: cortina: Fix MTU max setting

[Linus Walleij]

On Wed, Nov 8, 2023 at 3:26 PM Vladimir Oltean <olteanv@gmail.com> wrote:
> On Tue, Nov 07, 2023 at 10:54:26AM +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.
>
> What does this second paragraph intend to say? The patch doesn't use the
> BIT() macro.

Ah it's a leftover from v1 where I did some unrelated cleanup using
BIT() but Andrew remarked on it so I dropped it.

Maybe this twoliner in the commit message can be deleted when
applying?

Yours,
Linus Walleij

Re: [PATCH net v3 4/4] net: ethernet: cortina: Checksum only TCP and UDP

[Vladimir Oltean]

On Tue, Nov 07, 2023 at 10:54:29AM +0100, Linus Walleij wrote:
> It is a bit odd that frames that are neither TCP or UDP
> (such as ICMP or ARP) are still sent to the checksumming
> engine, where they are clearly just ignored.
> 
> Rewrite the logic slightly so that we first check if the
> frame is TCP or UDP, in that case bypass the checksum
> engine.
> 
> Reported-by: Vladimir Oltean <olteanv@gmail.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---

If this patch doesn't fix anything and isn't a dependency for anything,
it shouldn't be present in a series targeted for "net". And anyway, I
think it's not needed in general after the discussion on v2.

Re: [PATCH net v3 3/4] net: ethernet: cortina: Handle large frames

[Vladimir Oltean]

On Tue, Nov 07, 2023 at 10:54:28AM +0100, Linus Walleij wrote:
> The Gemini ethernet controller provides hardware checksumming
> for frames up to 1514 bytes including ethernet headers but not
> FCS.
> 
> If we start sending bigger frames (after first bumping up the MTU
> on both interfaces sending and receiveing the frames), truncated

s/receiveing/receiving/

> packets start to appear on the target such as in this tcpdump
> resulting from ping -s 1474:
> 
> 23:34:17.241983 14:d6:4d:a8:3c:4f (oui Unknown) > bc:ae:c5:6b:a8:3d (oui Unknown),
> ethertype IPv4 (0x0800), length 1514: truncated-ip - 2 bytes missing!
> (tos 0x0, ttl 64, id 32653, offset 0, flags [DF], proto ICMP (1), length 1502)
> OpenWrt.lan > Fecusia: ICMP echo request, id 1672, seq 50, length 1482
> 
> If we bypass the hardware checksumming and provide a software
> fallback, everything starts working fine up to the max TX MTU
> of 2047 bytes, for example ping -s2000 192.168.1.2:
> 
> 00:44:29.587598 bc:ae:c5:6b:a8:3d (oui Unknown) > 14:d6:4d:a8:3c:4f (oui Unknown),
> ethertype IPv4 (0x0800), length 2042:
> (tos 0x0, ttl 64, id 51828, offset 0, flags [none], proto ICMP (1), length 2028)
> Fecusia > OpenWrt.lan: ICMP echo reply, id 1683, seq 4, length 2008
> 
> The bit enabling to bypass hardware checksum (or any of the
> "TSS" bits) are undocumented in the hardware reference manual.
> The entire hardware checksum unit appears undocumented. The
> conclusion that we need to use the "bypass" bit was found by
> trial-and-error.
> 
> Since no hardware checksum will happen, we slot in a software
> checksum fallback.
> 
> Check for the condition where we need to compute checksum on the
> skb with either hardware or software using == CHECKSUM_PARTIAL instead
> of != CHECKSUM_NONE which is an incomplete check according to
> <linux/skbuff.h>.
> 
> We delete the code disabling the hardware checksum for large
> MTU:s: this is suboptimal because it will disable hardware

"MTUs" maybe?

> checksumming also on small packets which the checksumming
> engine can handle just fine, which is a waste of resources.
> 
> On the D-Link DIR-685 router this fixes a bug on the conduit
> interface to the RTL8366RB DSA switch: as the switch needs to add
> space for its tag it increases the MTU on the conduit interface
> to 1504 and that means that when the router sends packages
> of 1500 bytes these get an extra 4 bytes of DSA tag and the
> transfer fails because of the erroneous hardware checksumming,
> affecting such basic functionality as the LuCI web interface.
> 
> Suggested-by: Vladimir Oltean <olteanv@gmail.com>
> Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>  drivers/net/ethernet/cortina/gemini.c | 34 +++++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
> index b21a94b4ab5c..78287cfcbf63 100644
> --- a/drivers/net/ethernet/cortina/gemini.c
> +++ b/drivers/net/ethernet/cortina/gemini.c
> @@ -1145,6 +1145,7 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
>  	dma_addr_t mapping;
>  	unsigned short mtu;
>  	void *buffer;
> +	int ret;
>  
>  	mtu  = ETH_HLEN;
>  	mtu += netdev->mtu;
> @@ -1159,9 +1160,30 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
>  		word3 |= mtu;
>  	}
>  
> -	if (skb->ip_summed != CHECKSUM_NONE) {
> +	if (skb->len >= ETH_FRAME_LEN) {
> +		/* Hardware offloaded checksumming isn't working on frames
> +		 * bigger than 1514 bytes. A hypothesis about this is that the
> +		 * checksum buffer is only 1518 bytes, so when the frames get
> +		 * bigger they get truncated, or the last few bytes get
> +		 * overwritten by the FCS.
> +		 *
> +		 * Just use software checksumming and bypass on bigger frames.
> +		 */
> +		if (skb->ip_summed == CHECKSUM_PARTIAL) {
> +			ret = skb_checksum_help(skb);
> +			if (ret)
> +				return ret;
> +		}
> +		word1 |= TSS_BYPASS_BIT;
> +	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
>  		int tcp = 0;
>  
> +		/* We do not switch off the checksumming on non TCP/UDP
> +		 * frames: as is shown from tests, the checksumming engine
> +		 * is smart enough to see that a frame is not actually TCP
> +		 * or UDP and then just pass it through without any changes
> +		 * to the frame.
> +		 */
>  		if (skb->protocol == htons(ETH_P_IP)) {
>  			word1 |= TSS_IP_CHKSUM_BIT;
>  			tcp = ip_hdr(skb)->protocol == IPPROTO_TCP;
> @@ -1978,15 +2000,6 @@ static int gmac_change_mtu(struct net_device *netdev, int new_mtu)
>  	return 0;
>  }
>  
> -static netdev_features_t gmac_fix_features(struct net_device *netdev,
> -					   netdev_features_t features)
> -{
> -	if (netdev->mtu + ETH_HLEN + VLAN_HLEN > MTU_SIZE_BIT_MASK)
> -		features &= ~GMAC_OFFLOAD_FEATURES;
> -
> -	return features;
> -}
> -

I think this entire ndo_fix_features() can be indeed removed, but your
justification was not immediately convincing. I'd point out that after
your patch 1/4 "net: ethernet: cortina: Fix MTU max setting", you
actually made this dead code, because netdev->mtu can't be larger than
netdev->max_mtu.

If you reverse the patch order a bit, such that "net: ethernet: cortina:
Handle large frames" comes first, I think it would be much more logical
for the removal of gmac_fix_features() to be part of the commit
"net: ethernet: cortina: Fix MTU max setting", with the simple
justification: the new MTU makes the code stop having any role.

>  static int gmac_set_features(struct net_device *netdev,
>  			     netdev_features_t features)
>  {
> @@ -2212,7 +2225,6 @@ static const struct net_device_ops gmac_351x_ops = {
>  	.ndo_set_mac_address	= gmac_set_mac_address,
>  	.ndo_get_stats64	= gmac_get_stats64,
>  	.ndo_change_mtu		= gmac_change_mtu,
> -	.ndo_fix_features	= gmac_fix_features,
>  	.ndo_set_features	= gmac_set_features,
>  };
>  
> 
> -- 
> 2.34.1
> 

Re: [PATCH net v3 1/4] net: ethernet: cortina: Fix MTU max setting

[Vladimir Oltean]

On Wed, Nov 08, 2023 at 03:37:28PM +0100, Linus Walleij wrote:
> On Wed, Nov 8, 2023 at 3:26 PM Vladimir Oltean <olteanv@gmail.com> wrote:
> > On Tue, Nov 07, 2023 at 10:54:26AM +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.
> >
> > What does this second paragraph intend to say? The patch doesn't use the
> > BIT() macro.
> 
> Ah it's a leftover from v1 where I did some unrelated cleanup using
> BIT() but Andrew remarked on it so I dropped it.
> 
> Maybe this twoliner in the commit message can be deleted when
> applying?

I think it's better if you do it, there are some more minor fixups which
you could bundle up with a new series.