netdev - Re: [PATCH net-next V6 09/13] devlink: Add 'keep_link

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Message-ID: <abdde2b3-8f21-4970-9cf3-d250ca3fb5c6@intel.com>
Date: Tue, 2 Sep 2025 14:57:35 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Saeed Mahameed <saeed@...nel.org>, Jakub Kicinski <kuba@...nel.org>
CC: "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>, Saeed Mahameed <saeedm@...dia.com>,
	<netdev@...r.kernel.org>, Tariq Toukan <tariqt@...dia.com>, Gal Pressman
	<gal@...dia.com>, Leon Romanovsky <leonro@...dia.com>, Jiri Pirko
	<jiri@...dia.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next V6 09/13] devlink: Add 'keep_link_up' generic
 devlink device param



On 8/28/2025 1:09 PM, Saeed Mahameed wrote:
> On 10 Jul 15:24, Jakub Kicinski wrote:
>> On Wed, 9 Jul 2025 23:04:07 -0700 Saeed Mahameed wrote:
>>> On 09 Jul 19:58, Jakub Kicinski wrote:
>>>> On Tue,  8 Jul 2025 20:04:51 -0700 Saeed Mahameed wrote:
>>>>> Devices that support this in permanent mode will be requested to keep the
>>>>> port link up even when driver is not loaded, netdev carrier state won't
>>>>> affect the physical port link state.
>>>>>
>>>>> This is useful for when the link is needed to access onboard management
>>>>> such as BMC, even if the host driver isn't loaded.
>>>>
>>>> Dunno. This deserves a fuller API, and it's squarely and netdev thing.
>>>> Let's not add it to devlink.
>>>
>>> I don't see anything missing in the definition of this parameter
>>> 'keep_link_up' it is pretty much self-explanatory, for legacy reasons the
>>> netdev controls the underlying physical link state. But this is not
>>> true anymore for complex setups (multi-host, DPU, etc..).
>>
>> The policy can be more complex than "keep_link_up"
>> Look around the tree and search the ML archives please.
>>
> 
> Sorry for replying late, had to work on other stuff and was waiting
> internally for a question I had to ask about this, only recently got the
> answer.
> 
> I get your point, but I am not trying to implement any link policy
> or eth link specification tunables. For me and maybe other vendors
> this knob makes sense, and Important for the usecase I described.
> 
> Perhaps move it to a vendor specific knob ? or rename to
> link_{fw/soc}_controlled?
> 

Intel has also tried something similar sounding with the
"link_down_on_close" in ethtool, which appears to be have made it in to
ice and i40e.. (I thought I remembered these flags being rejected but I
guess not?) I guess the ethtool flag is a bit difference since its
relating to driver behavior when you bring the port down
administratively, vs something like this which affects firmware control
of the link regardless of its state to the kernel.

>>> This is not different as BMC is sort of multi-host, and physical link
>>> control here is delegated to the firmware.
>>>
>>> Also do we really want netdev to expose API for permanent nic tunables ?
>>> I thought this is why we invented devlink to offload raw NIC underlying
>>> tunables.
>>
>> Are you going to add devlink params for link config?
>> Its one of the things that's written into the NVMe, usually..
> 
> No, the purpose of this NVM series is to setup FW boot parameters and not spec related
> tunables.
> 

This seems quite useful to me w.r.t to BMC access. I think its a stretch
to say this implies the desire to add many other knobs.


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