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

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Date:   Tue, 21 Feb 2023 17:20:27 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Andrew Lunn <andrew@...n.ch>
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, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] net: lan743x: LAN743X selects FIXED_PHY to resolve a
 link error

+Arnd

On Tue, Feb 21, 2023 at 03:29:39AM +0100, Andrew Lunn wrote:
> 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.

Yes, that would be a good improvement.

Perhaps a fixes tag too?

> > 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.

I _think_ the patch, which uses select FIXED_PHY for LAN743X,
achieves that.

I CCed Arnd in case he has any input. Though I think I read
in an recent email from him that he is out most of this week.