linux-kernel - Re: [PATCH V3 2/5] misc: mlx5ctl: Add mlx5ctl misc driver

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Date:   Tue, 28 Nov 2023 09:52:00 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Saeed Mahameed <saeed@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Arnd Bergmann <arnd@...db.de>,
        Leon Romanovsky <leonro@...dia.com>,
        Jiri Pirko <jiri@...dia.com>, Leonid Bloch <lbloch@...dia.com>,
        Itay Avraham <itayavr@...dia.com>,
        linux-kernel@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH V3 2/5] misc: mlx5ctl: Add mlx5ctl misc driver

On 11/28/23 7:53 AM, Jakub Kicinski wrote:
> On Mon, 27 Nov 2023 21:46:28 -0700 David Ahern wrote:
>>> You keep saying "debug information" which is really underselling this
>>> driver. Are you not going to support mstreg?
>>>
>>> The common development flow as far as netdev is concerned is:
>>>  - some customer is interested in a new feature of a chip
>>>  - vendor hacks the support out of tree, using oot module and/or
>>>    user space tooling
>>>  - customer does a PoC with that hacked up, non-upstream solution
>>>    - if it works, vendor has to find out a proper upstream API,
>>>      hopefully agreed on with other vendors
>>>    - if it doesn't match customer needs the whole thing lands in the bin
>>>
>>> If the vendor specific PoC can be achieved with fully upstream software
>>> we lose leverage to force vendors to agree on common APIs.  
>>
>> Please elaborate on what "common" API there is to create here?
> 
> Damn, am I so bad at explaining basic things or y'all are spending
> 5 seconds reading this and are not really paying attention? :|
> 
>> Do you agree that each ASIC in the device is unique and hence will
>> have made different trade offs - both features and nerd knobs to tune
>> and affect the performance and runtime capabilities? If you do not
>> agree, then we need to have a different discussion ...
>> If you do, please elaborate on the outline of some common API that
>> could possibly be done here.
> 
> We have devlink params. If that doesn't scale we can look for other
> solutions but let's see them not scale _in practice_ first.
> 
>> You said no to the devlink parameters as a way to tune an ASIC.
> 
> What? When?

Jason responded with the same LPC reference, so I will only add a
reference to the slides for interested parties:

https://lpc.events/event/16/contributions/1359/attachments/1092/2094/FW-Centric-devices.pdf

> 
> Sounds like you'd like a similar open-ended interface for your device.

That's the danger of chiming in on threads like this - people drawing
conclusions they should not.

My interest on this thread is along the same lines for commenting during
both the LPC 2022 discussion and again at netconf this year - trying to
understand and keep track of the strongly held opinions of maintainers
and what options are deemed off limits for similar needs. No vendor
wants to go in circles redesigning and rewriting s/w.