From: Ivan Malov <ivan.malov@oktetlabs.ru>
To: Ferruh Yigit <ferruh.yigit@amd.com>
Cc: dev@dpdk.org, Qi Z Zhang <qi.z.zhang@intel.com>,
Qiming Yang <qiming.yang@intel.com>,
Wenjun Wu <wenjun1.wu@intel.com>,
Thomas Monjalon <thomas@monjalon.net>,
John McNamara <john.mcnamara@intel.com>,
Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>,
Jerin Jacob Kollanukkaran <jerinj@marvell.com>
Subject: Re: Understanding RX_OFFLOAD_VLAN_EXTEND
Date: Tue, 1 Nov 2022 00:56:52 +0300 (MSK) [thread overview]
Message-ID: <a75b5316-3ec2-25c1-2be7-43bbf898582@oktetlabs.ru> (raw)
In-Reply-To: <97a009d2-87cf-c901-590d-7c4dad37d6ca@amd.com>
[-- Attachment #1: Type: text/plain, Size: 2456 bytes --]
Thank you, Ferruh. You have been most helpful.
On Mon, 31 Oct 2022, Ferruh Yigit wrote:
> On 10/31/2022 6:46 PM, Ivan Malov wrote:
>> Hi!
>>
>> We have a hard time figuring out what the API contract of
>> RX_OFFLOAD_VLAN_EXTEND might be. The best educated guess
>> we can make is that the feature might have something to
>> do with identifying VLAN packets and extracting TCI
>> without stripping the tags from incoming packets.
>>
>> Is this understanding correct?
>>
>> You see, things aren't helped by the offload bit having
>> almost no commentary. Such could've shed light on its
>> meaning. Perhaps this gap in documentation should
>> be addressed somehow. Any opinions?
>>
>> Thank you.
>
>
> Hi Ivan,
>
> It is legacy from ixgbe driver, you can find more details on the ixgbe
> (82599) datasheet [1].
>
> RX_OFFLOAD_VLAN_EXTEND is *like*, QinQ but not, that is why we have
> 'QINQ_STRIP' offload.
>
> And RX_OFFLOAD_VLAN_EXTEND is more a configuration option, briefly you can
> ignore it.
> But in detail that is to configure device in a mode that it knows that
> received packets always has at least one VLAN tag, I assume it is for a case
> that some in the middle networking device inserts/requires VLAN tags. But
> optionally packet can have two VLAN tags. But as far as I can see this is not
> for to strip the VLAN tag or to filter packet based on it, this is just to
> configure device for this environment.
>
>
>
> [1] copy/paste from a public datasheet
> (http://iommu.com/datasheets/ixgbe-datasheets/82599-datasheet-v3-4.pdf), not
> sure if this is up to date version, but I think it is OK for this context:
>
> Double VLAN and Single VLAN Support
> The 82599 supports a mode where all received and sent packets have at least
> one VLAN tag in addition to the regular tagging that might optionally be
> added. In this document, when a packet carries two VLAN headers, the first
> header is referred to as an outer VLAN and the second header as an inner VLAN
> header (as listed in the table that follows). This mode is used for systems
> where the near end switch adds the outer VLAN header containing switching
> information. This mode is enabled by the following configuration:
> • This mode is activated by setting the DMATXCTL.GDV and the Extended VLAN
> bit in the CTRL_EXT register.
> • The EtherType of the VLAN tag used for the additional VLAN is defined in
> the VET EXT field in the EXVET register.
>
prev parent reply other threads:[~2022-10-31 21:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-31 18:46 Ivan Malov
2022-10-31 20:15 ` Ferruh Yigit
2022-10-31 21:56 ` Ivan Malov [this message]
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