From: Stephane Graber <stgraber@ubuntu.com>

All packets on ingress (except for jumbo) are terminated with a 4-bytes
CRC checksum. It's the responsability of the driver to strip those 4
bytes. Unfortunately a change dating back to March 2017 re-shuffled some
code and made the CRC stripping code effectively dead.

This change re-orders that part a bit such that the datalen is
immediately altered if needed.

Fixes: 4902a92270fb ("drivers: net: xgene: Add workaround for errata 10GE_8/ENET_11")
Signed-off-by: Stephane Graber <stgraber@ubuntu.com>
Tested-by: Stephane Graber <stgraber@ubuntu.com>
Cc: stable@vger.kernel.org
---
 drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
index ff2d099aab21..3892790f04e0 100644
--- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
+++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
@@ -696,6 +696,12 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
 	buf_pool->rx_skb[skb_index] = NULL;
 
 	datalen = xgene_enet_get_data_len(le64_to_cpu(raw_desc->m1));
+
+	/* strip off CRC as HW isn't doing this */
+	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
+	if (!nv)
+		datalen -= 4;
+
 	skb_put(skb, datalen);
 	prefetch(skb->data - NET_IP_ALIGN);
 	skb->protocol = eth_type_trans(skb, ndev);
@@ -717,10 +723,7 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
 		}
 	}
 
-	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
 	if (!nv) {
-		/* strip off CRC as HW isn't doing this */
-		datalen -= 4;
 		goto skip_jumbo;
 	}
 
-- 
2.34.1

On Thu, 17 Mar 2022 10:42:25 -0400 Stéphane Graber wrote:
> From: Stephane Graber <stgraber@ubuntu.com>
> 
> All packets on ingress (except for jumbo) are terminated with a 4-bytes
> CRC checksum. It's the responsability of the driver to strip those 4
> bytes. Unfortunately a change dating back to March 2017 re-shuffled some
> code and made the CRC stripping code effectively dead.
> 
> This change re-orders that part a bit such that the datalen is
> immediately altered if needed.
> 
> Fixes: 4902a92270fb ("drivers: net: xgene: Add workaround for errata 10GE_8/ENET_11")
> Signed-off-by: Stephane Graber <stgraber@ubuntu.com>
> Tested-by: Stephane Graber <stgraber@ubuntu.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
> index ff2d099aab21..3892790f04e0 100644
> --- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
> +++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
> @@ -696,6 +696,12 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
>  	buf_pool->rx_skb[skb_index] = NULL;
>  
>  	datalen = xgene_enet_get_data_len(le64_to_cpu(raw_desc->m1));
> +
> +	/* strip off CRC as HW isn't doing this */
> +	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
> +	if (!nv)
> +		datalen -= 4;

Alternatively we could call skb_trim() below to remove the FCS.
You call, but..

>  	skb_put(skb, datalen);
>  	prefetch(skb->data - NET_IP_ALIGN);
>  	skb->protocol = eth_type_trans(skb, ndev);
> @@ -717,10 +723,7 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
>  		}
>  	}
>  
> -	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
>  	if (!nv) {
> -		/* strip off CRC as HW isn't doing this */
> -		datalen -= 4;
>  		goto skip_jumbo;
>  	}

If you stick to moving the datalen adjustments this if will have a
single statement so according to the kernel code style it has to lose
the brackets.

From: Stephane Graber <stgraber@ubuntu.com>

All packets on ingress (except for jumbo) are terminated with a 4-bytes
CRC checksum. It's the responsability of the driver to strip those 4
bytes. Unfortunately a change dating back to March 2017 re-shuffled some
code and made the CRC stripping code effectively dead.

This change re-orders that part a bit such that the datalen is
immediately altered if needed.

Fixes: 4902a92270fb ("drivers: net: xgene: Add workaround for errata 10GE_8/ENET_11")
Signed-off-by: Stephane Graber <stgraber@ubuntu.com>
Tested-by: Stephane Graber <stgraber@ubuntu.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: stable@vger.kernel.org
---
 drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
index ff2d099aab21..53dc8d5fede8 100644
--- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
+++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
@@ -696,6 +696,12 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
 	buf_pool->rx_skb[skb_index] = NULL;
 
 	datalen = xgene_enet_get_data_len(le64_to_cpu(raw_desc->m1));
+
+	/* strip off CRC as HW isn't doing this */
+	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
+	if (!nv)
+		datalen -= 4;
+
 	skb_put(skb, datalen);
 	prefetch(skb->data - NET_IP_ALIGN);
 	skb->protocol = eth_type_trans(skb, ndev);
@@ -717,12 +723,8 @@ static int xgene_enet_rx_frame(struct xgene_enet_desc_ring *rx_ring,
 		}
 	}
 
-	nv = GET_VAL(NV, le64_to_cpu(raw_desc->m0));
-	if (!nv) {
-		/* strip off CRC as HW isn't doing this */
-		datalen -= 4;
+	if (!nv)
 		goto skip_jumbo;
-	}
 
 	slots = page_pool->slots - 1;
 	head = page_pool->head;
-- 
2.34.1