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

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Message-ID: <2025071736-viscous-entertain-ff6c@gregkh>
Date: Thu, 17 Jul 2025 18:21:58 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: 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>,
	Leon Romanovsky <leon@...nel.org>, 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 Thu, Jul 17, 2025 at 12:04:15PM -0400, Sean Anderson wrote:
> On 7/17/25 11:59, Greg Kroah-Hartman wrote:
> > On Thu, Jul 17, 2025 at 11:49:37AM -0400, Sean Anderson wrote:
> >> On 7/16/25 01:09, Greg Kroah-Hartman wrote:
> >> > On Tue, Jul 15, 2025 at 08:01:07PM -0400, Sean Anderson wrote:
> >> >> Support creating auxiliary devices with the id included as part of the
> >> >> name. This allows for hexadecimal ids, which may be more appropriate for
> >> >> auxiliary devices created as children of memory-mapped devices. If an
> >> >> auxiliary device's id is set to AUXILIARY_DEVID_NONE, the name must
> >> >> be of the form "name.id".
> >> >> 
> >> >> With this patch, dmesg logs from an auxiliary device might look something
> >> >> like
> >> >> 
> >> >> [    4.781268] xilinx_axienet 80200000.ethernet: autodetected 64-bit DMA range
> >> >> [   21.889563] xilinx_emac.mac xilinx_emac.mac.80200000 net4: renamed from eth0
> >> >> [   32.296965] xilinx_emac.mac xilinx_emac.mac.80200000 net4: PHY [axienet-80200000:05] driver [RTL8211F Gigabit Ethernet] (irq=70)
> >> >> [   32.313456] xilinx_emac.mac xilinx_emac.mac.80200000 net4: configuring for inband/sgmii link mode
> >> >> [   65.095419] xilinx_emac.mac xilinx_emac.mac.80200000 net4: Link is Up - 1Gbps/Full - flow control rx/tx
> >> >> 
> >> >> this is especially useful when compared to what might happen if there is
> >> >> an error before userspace has the chance to assign a name to the netdev:
> >> >> 
> >> >> [    4.947215] xilinx_emac.mac xilinx_emac.mac.1 (unnamed net_device) (uninitialized): incorrect link mode  for in-band status
> >> >> 
> >> >> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> >> >> ---
> >> >> 
> >> >> Changes in v2:
> >> >> - Add example log output to commit message
> >> > 
> >> > I rejected v1, why is this being sent again?
> >> 
> >> You asked for explanation, I provided it. I specifically pointed out why
> >> I wanted to do things this way. But I got no response. So here in v2.
> > 
> > Again, I said, "do not do that, this is not how ids work in the driver
> > model", and you tried to show lots of reasons why you wanted to do it
> > this way despite me saying so.
> > 
> > So again, no, sorry, this isn't ok.  Don't attempt to encode information
> > in a device id like you are trying to do here, that's not what a device
> > id is for at all.  I need to go dig up my old patch that made all device
> > ids random numbers just to see what foolish assumptions busses and
> > userspace tools are making....
> 
> But it *is* how ids work in platform devices.

No one should ever use platform devices/bus as an excuse to do anything,
it's "wrong" in so many ways, but needs to be because of special
reasons.  No other bus should work like that, sorry.

> And because my auxiliary
> devices are created by a platform device, it is guaranteed that the
> platform device id is unique and that it will also be unique for
> auxiliary devices. So there is no assumption here about the uniqueness
> of any given id.

Then perhaps use the faux device api instead?

thanks,

greg k-h