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

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Message-ID: <20180329140544.GB12066@piout.net>
Date:   Thu, 29 Mar 2018 16:05:44 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Andrew Lunn <andrew@...n.ch>
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 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.

Anyway, I'll remove that loop for now because I'm only supporting DT.
I'll get back to that later.


-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com