linux-kernel - Re: [PATCH net v2 1/4] auxiliary: Support hexadecimal ids

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Message-ID: <991cbb9a-a1b5-4ab8-9deb-9ecea203ce0f@linux.dev>
Date: Thu, 24 Jul 2025 09:55:59 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Leon Romanovsky <leon@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, Dave Ertman <david.m.ertman@...el.com>,
 Saravana Kannan <saravanak@...gle.com>, linux-kernel@...r.kernel.org,
 Michal Simek <michal.simek@....com>, linux-arm-kernel@...ts.infradead.org,
 Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH net v2 1/4] auxiliary: Support hexadecimal ids

On 7/23/25 04:13, Leon Romanovsky wrote:
> On Mon, Jul 21, 2025 at 10:29:32AM -0400, Sean Anderson wrote:
>> On 7/20/25 04:17, Leon Romanovsky wrote:
>> > On Thu, Jul 17, 2025 at 01:12:08PM -0400, Sean Anderson wrote:
>> >> On 7/17/25 12:33, Greg Kroah-Hartman wrote:
>> > 
>> > <...>
>> > 
>> >> Anyway, if you really think ids should be random or whatever, why not
>> >> just ida_alloc one in axiliary_device_init and ignore whatever's
>> >> provided? I'd say around half the auxiliary drivers just use 0 (or some
>> >> other constant), which is just as deterministic as using the device
>> >> address.
>> > 
>> > I would say that auxiliary bus is not right fit for such devices. This
>> > bus was introduced for more complex devices, like the one who has their
>> > own ida_alloc logic.
>> 
>> I'd say that around 2/3 of the auxiliary drivers that have non-constant
>> ids use ida_alloc solely for the auxiliary bus and for no other purpose.
>> I don't think that's the kind of complexity you're referring to.
>> 
>> >> Another third use ida_alloc (or xa_alloc) so all that could be
>> >> removed.
>> > 
>> > These ID numbers need to be per-device.
>> 
>> Why? They are arbitrary with no semantic meaning, right?
> 
> Yes, officially there is no meaning, and this is how we would like to
> keep it.
> 
> Right now, they are very correlated with with their respective PCI function number.
> Is it important? No, however it doesn't mean that we should proactively harm user
> experience just because we can do it.
> 
> [leonro@c ~]$ l /sys/bus/auxiliary/devices/
> ,,,
> rwxrwxrwx 1 root root 0 Jul 21 15:25 mlx5_core.rdma.0 -> ../../../devices/pci0000:00/0000:00:02.7/0000:0
> 8:00.0/mlx5_core.rdma.0
> lrwxrwxrwx 1 root root 0 Jul 21 15:25 mlx5_core.rdma.1 -> ../../../devices/pci0000:00/0000:00:02.7/0000:0
> 8:00.1/mlx5_core.rdma

Well, I would certainly like to have semantic meaning for ids. But apparently
that is only allowed if you can sneak it past the review process.

--Sean