linux-kernel - Re: [PATCH net-next 3/8] net: mscc: Add MDIO driver

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Date:   Thu, 29 Mar 2018 16:40:41 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Allan Nielsen <Allan.Nielsen@...rosemi.com>,
        razvan.stefanescu@....com, po.liu@....com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org
Subject: Re: [PATCH net-next 3/8] net: mscc: Add MDIO driver

On Thu, Mar 29, 2018 at 04:05:44PM +0200, Alexandre Belloni wrote:
> On 23/03/2018 at 21:49:39 +0100, Andrew Lunn wrote:
> > On Fri, Mar 23, 2018 at 09:11:12PM +0100, Alexandre Belloni wrote:
> > > Add a driver for the Microsemi MII Management controller (MIIM) found on
> > > Microsemi SoCs.
> > > On Ocelot, there are two controllers, one is connected to the internal
> > > PHYs, the other one can communicate with external PHYs.
> > 
> > Hi Alexandre
> > 
> > This looks to be standalone. Such drivers we try to put in
> > drivers/net/phy.
> > 
> > > +static int mscc_miim_read(struct mii_bus *bus, int mii_id, int regnum)
> > > +{
> > > +	struct mscc_miim_dev *miim = bus->priv;
> > > +	u32 val;
> > > +	int ret;
> > > +
> > > +	mutex_lock(&miim->lock);
> > 
> > What are you locking against here?
> > 
> > And you don't appear to initialize the mutex anywhere.
> > 
> > > +static int mscc_miim_reset(struct mii_bus *bus)
> > > +{
> > > +	struct mscc_miim_dev *miim = bus->priv;
> > > +	int i;
> > > +
> > > +	if (miim->phy_regs) {
> > > +		writel(0, miim->phy_regs + MSCC_PHY_REG_PHY_CFG);
> > > +		writel(0x1ff, miim->phy_regs + MSCC_PHY_REG_PHY_CFG);
> > > +		mdelay(500);
> > > +	}
> > > +
> > > +	for (i = 0; i < PHY_MAX_ADDR; i++) {
> > > +		if (mscc_miim_read(bus, i, MII_PHYSID1) < 0)
> > > +			bus->phy_mask |= BIT(i);
> > > +	}
> > 
> > Why do this? Especially so for the external bus, where the PHYs might
> > have a GPIO reset line, and won't respond until the gpio is
> > released. The core code does that just before it scans the bus, or
> > just before it scans the particular address on the bus, depending on
> > the scope of the GPIO.
> > 
> 
> IIRC, this was needed when probing the bus without DT, in that case, the
> mdiobus_scan loop of __mdiobus_register() will fail when doing the
> get_phy_id for phys 0 to 31 because get_phy_id() transforms any error in
> -EIO and so it is impossible to register the bus. Other drivers have a
> similar code to handle that case.

Hi Alexandre

Do you mean mscc_miim_read() will return -EIO if there is no device on
the bus at the address trying to be read? Most devices just return
0xffff because there is a pull up on the data line, nothing is driving
it, so all 1's are read.

It sounds like the correct fix is for get_phy_id() to look at the
error code for mdiobus_read(bus, addr, MII_PHYSID1). If it is EIO and
maybe ENODEV, set *phy_id to 0xffffffff and return. The scan code
should then do the correct thing.

       Andrew