linux-kernel - Re: [PATCH v1] net: ag71xx: fix mdio subnode support

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Message-ID: <20190930142907.wo3tahtg7g7mvfmp@pengutronix.de>
Date:   Mon, 30 Sep 2019 16:29:07 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jay Cliburn <jcliburn@...il.com>,
        Chris Snook <chris.snook@...il.com>,
        linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v1] net: ag71xx: fix mdio subnode support

On Mon, Sep 30, 2019 at 03:42:09PM +0200, Andrew Lunn wrote:
> On Mon, Sep 30, 2019 at 11:33:10AM +0200, Oleksij Rempel wrote:
> > The driver was working with fixed phy without any noticeable issues. This bug
> > was uncovered by introducing dsa ar9331-switch driver.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> >  drivers/net/ethernet/atheros/ag71xx.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/atheros/ag71xx.c b/drivers/net/ethernet/atheros/ag71xx.c
> > index 6703960c7cf5..d1101eea15c2 100644
> > --- a/drivers/net/ethernet/atheros/ag71xx.c
> > +++ b/drivers/net/ethernet/atheros/ag71xx.c
> > @@ -526,7 +526,7 @@ static int ag71xx_mdio_probe(struct ag71xx *ag)
> >  	struct device *dev = &ag->pdev->dev;
> >  	struct net_device *ndev = ag->ndev;
> >  	static struct mii_bus *mii_bus;
> > -	struct device_node *np;
> > +	struct device_node *np, *mnp;
> >  	int err;
> >  
> >  	np = dev->of_node;
> > @@ -571,7 +571,9 @@ static int ag71xx_mdio_probe(struct ag71xx *ag)
> >  		msleep(200);
> >  	}
> >  
> > -	err = of_mdiobus_register(mii_bus, np);
> > +	mnp = of_get_child_by_name(np, "mdio");
> > +	err = of_mdiobus_register(mii_bus, mnp);
> > +	of_node_put(mnp);
> >  	if (err)
> >  		goto mdio_err_put_clk;
> 
> Hi Oleksij
> 
> You need to keep backwards compatibility here. If you find an mdio
> node, use it, but if not, you need to still register np.
> 
> This is also extending the driver binding, so you need to update the
> binding documentation.

Hi Andrew,

Normally i would agree. But in this case:
- this driver is freshly added to the kernel and is different to OpenWrt
  implementation any way. No users from this side.
- Devicetree binding says:
  Documentation/devicetree/bindings/net/qca,ar71xx.txt
|Optional properties:
|- phy-handle : phandle to the PHY device connected to this device.
|- fixed-link : Assume a fixed link. See fixed-link.txt in the same directory.
|  Use instead of phy-handle.
|
|Optional subnodes:
|- mdio : specifies the mdio bus, used as a container for phy nodes
|  according to phy.txt in the same directory

So, it is driver bug ...ooOO (my personal bug :D)

I would say: if some one already started to use this driver, didn't used
documentation and didn't reported this bug, can't really blame any one
here :)

Regards,
Oleksij
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