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

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Date:   Mon, 27 Nov 2023 16:07:19 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Saeed Mahameed <saeed@...nel.org>
Cc:     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 Mon, 27 Nov 2023 11:26:06 -0800 Saeed Mahameed wrote:
> This driver is different as it doesn't replace existing mlx5 drivers,
> mlx5 functionality drivers are still there to expose the device features
> through the standard stacks, this is just a companion driver to access
> debug information, by driver and FW design mlx5ctl is not meant to
> manage or pilot the device like other device specific char drivers.

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.

This should all be self-evident for people familiar with netdev, but
I thought I'd spell it out.

I understand that the device has other uses, but every modern NIC has
other uses. I don't see how netdev can agree to this driver as long as
there is potential for configuring random networking things thru it.
All major netdev vendors have a set of out of tree tools / "expose
everything misc drivers", "for debug". They will soon follow your
example if we let this in.