netdev - Re: [PATCH net v2] net: ftgmac100: Disable hardware checksum on AST2600

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Date:   Fri, 13 May 2022 07:11:25 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Joel Stanley <joel@....id.au>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Dylan Hung <dylan_hung@...eedtech.com>,
        David Wilder <dwilder@...ibm.com>, netdev@...r.kernel.org,
        openbmc@...ts.ozlabs.org, David Wilder <wilder@...ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: ftgmac100: Disable hardware checksum on
 AST2600

Dear Joel,


Am 13.05.22 um 01:19 schrieb Joel Stanley:
> The AST2600 when using the i210 NIC over NC-SI has been observed to
> produce incorrect checksum results with specific MTU values. This was
> first observed when sending data across a long distance set of networks.
> 
> On a local network, the following test was performed using a 1MB file of
> random data.
> 
> On the receiver run this script:
> 
>   #!/bin/bash
>   while [ 1 ]; do
>          # Zero the stats
>          nstat -r  > /dev/null
>          nc -l 9899 > test-file
>          # Check for checksum errors
>          TcpInCsumErrors=$(nstat | grep TcpInCsumErrors)
>          if [ -z "$TcpInCsumErrors" ]; then
>                  echo No TcpInCsumErrors
>          else
>                  echo TcpInCsumErrors = $TcpInCsumErrors
>          fi
>   done
> 
> On an AST2600 system:
> 
>   # nc <IP of  receiver host> 9899 < test-file
> 
> The test was repeated with various MTU values:
> 
>   # ip link set mtu 1410 dev eth0
> 
> The observed results:
> 
>   1500 - good
>   1434 - bad
>   1400 - good
>   1410 - bad
>   1420 - good

Sort the values? As some MTUs are good, should a allow list for these 
values be added?

> The test was repeated after disabling tx checksumming:
> 
>   # ethtool -K eth0 tx-checksumming off
> 
> And all MTU values tested resulted in transfers without error.
> 
> An issue with the driver cannot be ruled out, however there has been no
> bug discovered so far.
> 
> David has done the work to take the original bug report of slow data
> transfer between long distance connections and triaged it down to this
> test case.
> 
> The vendor suspects this this is a hardware issue when using NC-SI. The fixes line refers
> to the patch that introduced AST2600 support.

Please wrap the line after 75 characters.

Can the problem be reproduced with QEMU?

> Fixes: 39bfab8844a0 ("net: ftgmac100: Add support for DT phy-handle property")
> Reported-by: David Wilder <wilder@...ibm.com>
> Signed-off-by: Joel Stanley <joel@....id.au>

Should the intel-wired-lan folks be put in Cc?

> ---
> v2 updates the commit message with confirmation form the vendor that

from

> this is a hardware issue, and clarifes why the commit used in the fixes

clarifies

> tag was chosen.
> 
>   drivers/net/ethernet/faraday/ftgmac100.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
> index caf48023f8ea..5231818943c6 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -1928,6 +1928,11 @@ static int ftgmac100_probe(struct platform_device *pdev)
>   	/* AST2400  doesn't have working HW checksum generation */
>   	if (np && (of_device_is_compatible(np, "aspeed,ast2400-mac")))
>   		netdev->hw_features &= ~NETIF_F_HW_CSUM;
> +
> +	/* AST2600 tx checksum with NC-SI is broken */

Does ASPEED have an internal bug for this, so should there be new 
revisions of the AST2600, the bug can be fixed?

> +	if (priv->use_ncsi && of_device_is_compatible(np, "aspeed,ast2600-mac"))
> +		netdev->hw_features &= ~NETIF_F_HW_CSUM;
> +

I would fancy a note or even warning about this hardware issue.

>   	if (np && of_get_property(np, "no-hw-checksum", NULL))
>   		netdev->hw_features &= ~(NETIF_F_HW_CSUM | NETIF_F_RXCSUM);
>   	netdev->features |= netdev->hw_features;


Kind regards,

Paul