linux-kernel - Re: [RFC net-next 0/2] Introduce MDIO probe order C45 over C22

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Message-ID: <YLazBrpXbpsb6aXI@lunn.ch>
Date:   Wed, 2 Jun 2021 00:21:58 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Wong Vee Khee <vee.khee.wong@...ux.intel.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 0/2] Introduce MDIO probe order C45 over C22

On Tue, Jun 01, 2021 at 11:44:23PM +0800, Wong Vee Khee wrote:
> On Tue, Jun 01, 2021 at 03:04:51PM +0200, Andrew Lunn wrote:
> > On Tue, Jun 01, 2021 at 06:47:34PM +0800, Wong Vee Khee wrote:
> > > On Tue, May 25, 2021 at 03:34:34PM +0200, Andrew Lunn wrote:
> > > > On Tue, May 25, 2021 at 01:58:03PM +0800, Wong Vee Khee wrote:
> > > > > Synopsys MAC controller is capable of pairing with external PHY devices
> > > > > that accessible via Clause-22 and Clause-45.
> > > > > 
> > > > > There is a problem when it is paired with Marvell 88E2110 which returns
> > > > > PHY ID of 0 using get_phy_c22_id(). We can add this check in that
> > > > > function, but this will break swphy, as swphy_reg_reg() return 0. [1]
> > > > 
> > > > Is it possible to identify it is a Marvell PHY? Do any of the other
> > > > C22 registers return anything unique? I'm wondering if adding
> > > > .match_phy_device to genphy would work to identify it is a Marvell PHY
> > > > and not bind to it. Or we can turn it around, make the
> > > > .match_phy_device specifically look for the fixed-link device by
> > > > putting a magic number in one of the vendor registers.
> > > >
> > > 
> > > I checked the Marvell and did not see any unique register values.
> > > Also, since get_phy_c22_id() returns a *phy_id== 0, it is not bind to
> > > any PHY driver, so I don't think adding the match_phy_device check in
> > > getphy would help.
> > 
> > It has a Marvell ID in C45 space. So maybe we need to special case for
> > ID 0. If we get that, go look in C45 space. If we find a valid ID, use
> > it. If we get EOPNOTSUP because the MDIO bus is not C45 capable, or we
> > don't find a vendor ID in C45 space, keep with id == 0 and load
> > genphy?
> >
> 
> Make sense for me.
> Let me what you think of adding the checks in *get_phy_device():
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 1539ea021ac0..ad9a87fadea1 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -862,11 +862,21 @@ struct phy_device *get_phy_device(struct mii_bus *bus, int addr, bool is_c45)
>         c45_ids.mmds_present = 0;
>         memset(c45_ids.device_ids, 0xff, sizeof(c45_ids.device_ids));
> 
> -       if (is_c45)
> +       if (is_c45) {
>                 r = get_phy_c45_ids(bus, addr, &c45_ids);
> -       else
> +       } else {
>                 r = get_phy_c22_id(bus, addr, &phy_id);
> 
> +               if (phy_id == 0) {
> +                       r = get_phy_c45_ids(bus, addr, &c45_ids);
> +                       if (r == -ENOTSUPP || r == -ENODEV)
> +                               return 0;

This bit is not correct. I said 'or we don't find a vendor ID in C45
space, keep with id == 0'. We need to keep backwards compatibility. If
get_phy_c22_id() did not return an error we should create a device
with phy_id 0, if get_phy_c45_ids() returns an error.

     Andrew