netdev - Re: [PATCH] net: lan743x: LAN743X selects FIXED

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Date:   Tue, 21 Feb 2023 03:29:39 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     Tom Rix <trix@...hat.com>, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        steen.hegelund@...rochip.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: lan743x: LAN743X selects FIXED_PHY to resolve a
 link error

On Mon, Feb 20, 2023 at 07:46:13AM +0100, Simon Horman wrote:
> On Mon, Feb 20, 2023 at 02:19:34AM +0100, Andrew Lunn wrote:
> > On Sun, Feb 19, 2023 at 07:16:07PM +0100, Simon Horman wrote:
> > > On Sun, Feb 19, 2023 at 10:03:21AM -0500, Tom Rix wrote:
> > > > A rand config causes this link error
> > > > drivers/net/ethernet/microchip/lan743x_main.o: In function `lan743x_netdev_open':
> > > > drivers/net/ethernet/microchip/lan743x_main.c:1512: undefined reference to `fixed_phy_register'
> > > > 
> > > > lan743x_netdev_open is controlled by LAN743X
> > > > fixed_phy_register is controlled by FIXED_PHY
> > > > 
> > > > So LAN743X should also select FIXED_PHY
> > > > 
> > > > Signed-off-by: Tom Rix <trix@...hat.com>
> > > 
> > > Hi Tom,
> > > 
> > > I am a little confused by this.
> > > 
> > > I did manage to cook up a config with LAN743X=m and FIXED_PHY not set.
> > > But I do not see a build failure, and I believe that is because
> > > when FIXED_PHY is not set then a stub version of fixed_phy_register(),
> > > defined as static inline in include/linux/phy_fixed.h, is used.
> > > 
> > > Ref: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/include/linux/phy_fixed.h?h=main&id=675f176b4dcc2b75adbcea7ba0e9a649527f53bd#n42
> > 
> > I'n guessing, but it could be that LAN743X is built in, and FIXED_PHY
> > is a module? What might be needed is
> > 
> > depends on FIXED_PHY || FIXED_PHY=n
> 
> Thanks Andrew,
> 
> LAN743X=y and FIXED_PHY=m does indeed produce the problem that Tom
> describes. And his patch does appear to resolve the problem.

O.K. So the commit message needs updating to describe the actual
problem.

> Unfortunately your proposed solution seems to run foul of a complex
> dependency situation.

I was never any good at Kconfig. Arnd is the expert at solving
problems like this.

You want either everything built in, or FIXED_PHY built in and LAN743X
modular, or both modular.

     Andrew