linux-kernel - Re: [PATCH net 4/4] net: axienet: Split into MAC and MDIO drivers

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Message-ID: <3e2acebe-a9db-494b-bca8-2e1bbc3c1eaf@lunn.ch>
Date: Tue, 24 Jun 2025 00:45:14 +0200
From: Andrew Lunn <andrew@...n.ch>
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,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Michal Simek <michal.simek@....com>,
	Saravana Kannan <saravanak@...gle.com>,
	Leon Romanovsky <leon@...nel.org>,
	Dave Ertman <david.m.ertman@...el.com>,
	linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net 4/4] net: axienet: Split into MAC and MDIO drivers

On Mon, Jun 23, 2025 at 02:48:53PM -0400, Sean Anderson wrote:
> On 6/23/25 14:27, Andrew Lunn wrote:
> > On Mon, Jun 23, 2025 at 11:16:08AM -0400, Sean Anderson wrote:
> >> On 6/21/25 03:33, Andrew Lunn wrote:
> >> > On Thu, Jun 19, 2025 at 04:05:37PM -0400, Sean Anderson wrote:
> >> >> Returning EPROBE_DEFER after probing a bus may result in an infinite
> >> >> probe loop if the EPROBE_DEFER error is never resolved.
> >> > 
> >> > That sounds like a core problem. I also thought there was a time
> >> > limit, how long the system will repeat probes for drivers which defer.
> >> > 
> >> > This seems like the wrong fix to me.
> >> 
> >> I agree. My first attempt to fix this did so by ignoring deferred probes
> >> from child devices, which would prevent "recursive" loops like this one
> >> [1]. But I was informed that failing with EPROBE_DEFER after creating a
> >> bus was not allowed at all, hence this patch.
> > 
> > O.K. So why not change the order so that you know you have all the
> > needed dependencies before registering the MDIO bus?
> > 
> > Quoting your previous email:
> > 
> >> Returning EPROBE_DEFER after probing a bus may result in an infinite
> >> probe loop if the EPROBE_DEFER error is never resolved. For example,
> >> if the PCS is located on another MDIO bus and that MDIO bus is
> >> missing its driver then we will always return EPROBE_DEFER.
> > 
> > Why not get a reference on the PCS device before registering the MDIO
> > bus?
> 
> Because the PCS may be on the MDIO bus. This is probably the most-common
> case.

So you are saying the PCS is physically there, but the driver is
missing because of configuration errors? Then it sounds like a kconfig
issue?

Or are you saying the driver has been built but then removed from
/lib/modules/

	Andrew