linux-kernel - Re: [PATCH] net: dsa: mv88e6xxx: Make *_c45 callbacks agree with phy_*

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Date: Mon, 22 Jan 2024 07:46:06 -0800
From: Tim Menninger <tmenninger@...estorage.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, f.fainelli@...il.com, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: mv88e6xxx: Make *_c45 callbacks agree with
 phy_*_c45 callbacks

On Mon, Jan 22, 2024 at 7:12 AM Vladimir Oltean <olteanv@...il.com> wrote:
>
> On Mon, Jan 22, 2024 at 03:30:20PM +0100, Andrew Lunn wrote:
> > On Mon, Jan 22, 2024 at 02:33:49PM +0200, Vladimir Oltean wrote:
> > > On Tue, Jan 16, 2024 at 05:51:13PM -0800, Tim Menninger wrote:
> > > > My impression is still that the read_c45 function should agree with the
> > > > phy_read_c45 function, but that isn't a hill I care to die on if you still
> > > > think otherwise. Thoughts?
> > >
> > > FWIW, Tim's approach is consistent with what drivers/net/mdio/mdio-mux.c does.
> > >
> > >             if (parent_bus->read)
> > >                     cb->mii_bus->read = mdio_mux_read;
> > >             if (parent_bus->write)
> > >                     cb->mii_bus->write = mdio_mux_write;
> > >             if (parent_bus->read_c45)
> > >                     cb->mii_bus->read_c45 = mdio_mux_read_c45;
> > >             if (parent_bus->write_c45)
> > >                     cb->mii_bus->write_c45 = mdio_mux_write_c45;
> > >
> > > My only objection to his patch (apart from the commit message which
> > > should indeed be more detailed) is that I would have preferred the same
> > > "if" syntax rather than the use of a ternary operator with NULL.
> >
> > I agree it could be fixed this way. But what i don't like about the
> > current code is how C22 and C45 do different things with error
> > codes. Since the current code is trying to use an error code, i would
> > prefer to fix that error code handling, rather than swap to a
> > different way to indicate its not supported.
> >
> >         Andrew
>
> You did write in commit da099a7fb13d ("net: phy: Remove probe_capabilities")
> that the MDIO bus API is now this: "Deciding if to probe of PHYs using
> C45 is now determine by if the bus provides the C45 read method."
>
> Do you not agree that Tim's approach is the more straightforward
> solution overall to skip C45 PHY probing, given this API, both code wise
> and runtime wise? Are there downsides to it?
>
> I have no objection to the C22 vs C45 error code handling inconsistency.
> It can be improved, sure. But it also does not matter here, if we agree
> that this problem can be sorted out in a more straightforward way with
> no negative consequences.
>
> I sort of don't understand the desire to have the smallest patch in
> terms of lines of code, when the end result will end up being suboptimal
> compared to something with just a little more lines (1 vs 4).


Andrew, would you feel differently if I added to the patch the same
logic for C22 ops? Perhaps that symmetry should have existed
in the initial patch, e.g.

    bus->read = chip->info->ops->phy_read
        ? mv88e6xxx_mdio_read : NULL;
    bus->write = chip->info->ops->phy_write
        ? mv88e6xxx_mdio_write : NULL;
    bus->read_c45 = chip->info->ops->phy_read_c45
        ? mv88e6xxx_mdio_read_c45 : NULL;
    bus->write_c45 = chip->info->ops->phy_write_c45
        ? mv88e6xxx_mdio_write_c45 : NULL;

Vladimir, as far as style I have no objections moving to straightlined
if's. I most prefer to follow the convention the rest of the code follows
and can change my patch accordingly.