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From: Florian Fainelli <f.fainelli@gmail.com>
To: Andrew Lunn <andrew@lunn.ch>, Vladimir Oltean <olteanv@gmail.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>,
	woojung.huh@microchip.com, UNGLinuxDriver@microchip.com,
	vivien.didelot@gmail.com, davem@davemloft.net, kuba@kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum
Date: Thu, 15 Jul 2021 09:24:09 -0700	[thread overview]
Message-ID: <2ee678f6-07f3-6747-15a8-280cf1f7ca04@gmail.com> (raw)
In-Reply-To: <YPAzZXaC/En3s4ly@lunn.ch>

On 7/15/21 6:08 AM, Andrew Lunn wrote:
>> - If we inherit NETIF_F_HW_CSUM from the master for tail taggers, it is
>>   actively detrimential to keep this feature enabled, as proven my Lino.
>>   As for header taggers, I fail to see how this would be helpful, since
>>   the DSA master would always fail to see the real IP header (it has
>>   been pushed to the right by the DSA tag), and therefore, the DSA
>>   master offload would be effectively bypassed.
> 
> The Marvell MACs know about DSA and should be able to perform hardware
> checksumming. It is a long time since i looked at how this works, but
> i think there is a field in the descriptor which gets set with the
> offset to the IP header, so it work for DSA as well as EDSA.
> 
> I _think_ Broadcom MACs also know about Broadcom tags and can do the
> right thing.

Yes, the SYSTEMPORT MAC as well as bgmac to some extent will
automagically work, but they have to be told to expect a Broadcom tag in
order to generate an appropriate checksum on receive. This is why we
have this:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/broadcom/bcmsysport.c#n144

Likewise, for TX:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/broadcom/bcmsysport.c#n172
-- 
Florian

  parent reply	other threads:[~2021-07-15 16:24 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-14 19:17 [PATCH 0/2] Fixes for KSZ DSA switch Lino Sanfilippo
2021-07-14 19:17 ` [PATCH 1/2] net: dsa: tag_ksz: linearize SKB before adding DSA tag Lino Sanfilippo
2021-07-14 19:17 ` [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum Lino Sanfilippo
2021-07-14 19:48   ` Vladimir Oltean
2021-07-14 20:15     ` Andrew Lunn
2021-07-15  6:54       ` Vladimir Oltean
2021-07-15 11:16         ` Aw: " Lino Sanfilippo
2021-07-15 11:49           ` Vladimir Oltean
2021-07-15 13:04             ` Aw: " Lino Sanfilippo
2021-07-15 13:12               ` Vladimir Oltean
2021-07-15 13:34                 ` Aw: " Lino Sanfilippo
2021-07-15 13:08         ` Andrew Lunn
2021-07-15 14:36           ` Vladimir Oltean
2021-07-15 15:50             ` Andrew Lunn
2021-07-19  8:20             ` Aw: " Lino Sanfilippo
2021-07-19  8:24               ` Vladimir Oltean
2021-07-15 16:24           ` Florian Fainelli [this message]
2021-07-15 23:23 ` [PATCH 0/2] Fixes for KSZ DSA switch Florian Fainelli
2021-07-16  8:49   ` Aw: " Lino Sanfilippo

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