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

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Message-ID: <aLC3jlzImChRDeJs@x130>
Date: Thu, 28 Aug 2025 13:09:50 -0700
From: Saeed Mahameed <saeed@...nel.org>
To: 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 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?

>> 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.