Re: [PATCH RFC net-next 0/2] pds_core: add switchdev and tc for vlan offload

[Shannon Nelson <shannon.nelson@amd.com>]

On 4/28/23 3:52 PM, Samudrala, Sridhar wrote:
> 
> On 4/27/2023 11:45 AM, Shannon Nelson wrote:
>> This is an RFC for adding to the pds_core driver some very simple support
>> for VF representors and a tc command for offloading VF port vlans.
>>
>> The problem to solve is how to request that a NIC do the push/pop of port
>> vlans on a VF.  The initial pds_core patchset[0] included this support
>> through the legacy ip-link methods with a PF netdev that had no datapath,
>> simply existing to enable commands such as
>>      ip link set <pf> vf <vfid> vlan <vid>
>> This was soundly squashed with a request to create proper VF 
>> representors.
>> The pds_core driver has since been reworked and merged without this 
>> feature.
>>
>> This pair of patches is a first attempt at adding support for a simple
>> VF representor and tc offload which I've been tinkering with off and
>> on over the last few weeks.  I will acknowledge that we have no proper
>> filtering offload language in our firmware's adminq interface yet.
>> This has been mentioned internally and is a "future project" with no
>> actual schedule yet.  Given that, I have worked here with what I have,
>> using the existing vf_setattr function.
>>
>> An alternative that later occured to me is to make this a "devlink port
>> function" thing, similar to the existing port mac.  This would have the
>> benefit of using a familiar concept from and similar single command as
>> the legacy method, would allow early port setup as with setting the mac
>> and other port features, and would not need to create a lot of mostly
>> empty netdevs for the VF representors.  I don't know if this would then
>> lead to adding "trust" and "spoofcheck" as well, but I'm not aware of any
>> other solutions for them, either.  This also might make more sense for
>> devices that don't end up as user network interfaces, such as a virtio
>> block device that runs over ethernet on the back end.  I don't have RFC
>> code for this idea, but thought I would toss it out for discussion -
>> I didn't see any previous related discussion in a (rather quick) search.
>>
>> I welcome your comments and suggestions.
> 
> Adding a tc rule doesn't seem to be the right interface to
> configure port-vlan for all packets sent/received on a port.
> tc would be appropriate if we want to do push/pop vlan on certain flows.

This is something that had occurred to me.  The tc commands seem to be 
aimed at a finer grain control than what I need for this case.

> 
>    bridge vlan add dev $VF_REP vid 200 pvid untagged master
> would be a better option. This may require adding vf reps to a bridge
> and enable vlan_filtering on the bridge. The driver needs to register
> for SWITCHDEV_PORT_OBJ_ADD events.

I thought about this as well, but this also seems to be abusing the 
model when there are no data streams and no representor for the PF.

> 
> Extending devlink port function to support port-vlan similar to setting
> a mac address also looks like a good option without the requirement of
> having to add port reps to a bridge.

I'm hoping that others will chime in on this idea.  Meanwhile, I'll see 
if I can work up an RFC for this thought later this week.

sln

> 
>>
>> Thanks,
>> sln
>>
>> [0]: 
>> https://lore.kernel.org/netdev/20221118225656.48309-1-snelson@pensando.io/
>>
>> Shannon Nelson (2):
>>    pds_core: netdev representors for each VF
>>    pds_core: tc command handling for vlan push-pop
>>
>>   drivers/net/ethernet/amd/pds_core/Makefile |   1 +
>>   drivers/net/ethernet/amd/pds_core/core.h   |  12 +
>>   drivers/net/ethernet/amd/pds_core/main.c   |  28 +-
>>   drivers/net/ethernet/amd/pds_core/rep.c    | 322 +++++++++++++++++++++
>>   4 files changed, 361 insertions(+), 2 deletions(-)
>>   create mode 100644 drivers/net/ethernet/amd/pds_core/rep.c
>>