smsc95xx: Add support for automated PHY address detection

[Andrew Lunn <andrew@lunn.ch>]

On Sun, Dec 23, 2018 at 11:43:05AM +0100, Marek Vasut wrote:
> On 12/23/18 11:23 AM, Andrew Lunn wrote:
> >>> +static int smsc95xx_phy_address(struct usbnet *dev)
> >>> +{
> >>> +	u32 read_buf;
> >>> +	int ret, id1, id2, phyad;
> >>> +
> >>> +	ret = smsc95xx_read_reg(dev, HW_CFG, &read_buf);
> >>> +	if (ret < 0)
> >>> +		return ret;
> >>> +
> >>> +	/* Check if using external PHY, if not, use internal PHY address */
> >>> +	if (!(read_buf & HW_CFG_PSEL_))
> >>> +		return SMSC95XX_INTERNAL_PHY_ID;
> >>> +
> >>> +	/*
> >>> +	 * Detect external PHY address. Here we probe the MDIO bus from
> >>> +	 * the highest address, since some PHYs respond also on address
> >>> +	 * zero, which they consider MDIO broadcast address. We really
> >>> +	 * want to get their proper address instead though, so we scan
> >>> +	 * address zero last.
> >>> +	 */
> >>> +	for (phyad = 0x1f; phyad >= 0; phyad--) {
> >>> +		id1 = smsc95xx_mdio_read(dev->net, phyad, MII_PHYSID1);
> >>> +		id2 = smsc95xx_mdio_read(dev->net, phyad, MII_PHYSID2);
> >>> +		/* Check for valid response from the PHY */
> >>> +		if (id1 > 0 && id2 > 0 && id1 != 0x7fff && id2 != 0xffff)
> >>> +			return phyad;
> >>> +	}
> > 
> > This would be so much easier if the driver used the core mdio/phy
> > code. Just set mdio->phy_mask to ~BIT(0) and then use
> > phy_find_first().
> 
> That's in the pipeline, along with PM cleanups, but low prio.

Great. Does using the broadcast address actually cause a problem?  If
not, i would say lets drop this part of the patch until you do the
cleanup.

     Andrew