Re: [RFC net-next 0/4] devlink: Add boot-time defaults

[Jiri Pirko]

Wed, May 13, 2026 at 07:53:05AM CEST, mbloch@xxxxxxxxxx wrote:
>
>
>On 12/05/2026 21:35, Jiri Pirko wrote:
>> Tue, May 12, 2026 at 05:25:21PM CEST, parav@xxxxxxxxxx wrote:
>>>
>>>
>>>> From: Jiri Pirko <jiri@xxxxxxxxxxx>
>>>> Sent: 12 May 2026 07:37 PM
>>>>
>>>> Tue, May 12, 2026 at 03:48:32PM CEST, parav@xxxxxxxxxx wrote:
>>>>>
>>>>>> From: Jiri Pirko <jiri@xxxxxxxxxxx>
>>>>>> Sent: 12 May 2026 02:16 PM
>>>>>>
>>>>>> Mon, May 11, 2026 at 08:21:37PM +0200, parav@xxxxxxxxxx wrote:
>>>>>>>
>>>>>>>> From: Mark Bloch <mbloch@xxxxxxxxxx>
>>>>>>>> Sent: 10 May 2026 06:02 PM
>>>>>>>>
>>>>>>>
>>>>>>> [..]
>>>>>>>
>>>>>>>>> I look at it from the perspective that from some CX generation,
>>>>>>>>> switchdev mode should be default. So that is a device-based decision.
>>>>>>>>> I believe as such it can optionally be permanenty configured (nv config)
>>>>>>>>> on older device. Why not?
>>>>>>>>
>>>>>>> Because sometimes switchdev_inactive is needed and sometimes not.
>>>>>>> Such knob is not device decision.
>>>>>>
>>>>>> That is what I would call corner case. In that, user can use userspace
>>>>>> configuration to change the mode in runtime.
>>>>>>
>>>>> Corner vs common depends on users one talks to. :)
>>>>> If fw has switchdev(active) as default, and then
>>>>> And user needs to run switchdev_inactive, it will actually break their switching applications.
>>>>
>>>> Can you describe the actutal breakage please?
>>>>
>>> Driver default was switchdev so all the traffic is forwarded to the switch,
>>> and user didn't have chance to setup the fdb rules.
>>> So packets are dropped but user didn't expect the traffic to be forwarded.
>> 
>> User may switch mode to switchdev_inactive early on, before any of the
>> representors are created. What's the issue then?
>
>That is the ordering problem I am trying to solve.
>
>On a DPU, the host PF cannot finish loading until the ECPF moves the eswitch to
>switchdev/switchdev_inactive. So we need to do that transition during ECPF
>driver init, as early as possible. Waiting for userspace means the host PF stays
>blocked until userspace is up and has the right logic.
>
>That is not always true in practice, the driver may be built in, loaded from an
>initramfs, or the initramfs may simply not contain the devlink policy we need.
>
>Also, after talking with Parav, my understanding is that we need to support both
>switchdev and switchdev_inactive, since different customers want different boot
>behavior. Once we do the transition, the host PF can load and may start sending
>packets. At that point the initial mode already matters: in switchdev_inactive
>packets are dropped until userspace programs the pipeline; in switchdev they may
>reach the FDB before the pipeline is ready.
>
>So I do not think an early userspace transition is equivalent here. The initial
>mode needs to be known by the kernel before userspace runs, which is why I am
>proposing the devlink= command line default.

Okay fair enough. Could you please at least make sure this is mode only
config and noone would ever think about abusing this for any other
configuration? Perhaps call it "devlink_eswitch_mode=" to remove
the "devlink=" namespace flexibility?