net: phy: at803x: Request 'reset' GPIO only for AT8030 PHY

commit 9eb13f65 upstream.

This removes the dependency on GPIOLIB for non faulty PHYs.

Indeed, without this patch, if GPIOLIB is not selected
devm_gpiod_get_optional() will return -ENOSYS and the driver probe
call will fail, regardless of the actual PHY hardware.

Out of the 3 PHYs supported by this driver (AT8030, AT8031, AT8035),
only AT8030 presents the issues that commit 13a56b44 ("net: phy:
at803x: Add support for hardware reset") attempts to work-around by
using a 'reset' GPIO line.

Hence, only AT8030 should depend on GPIOLIB operating properly.

Fixes: 13a56b44 ("net: phy: at803x: Add support for hardware reset")
Signed-off-by: Sebastian Frias <sf84@laposte.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/net/phy/at803x.c

@@ -197,12 +197,16 @@ static int at803x_probe(struct phy_device *phydev)
 	if (!priv)
 		return -ENOMEM;
 
+	if (phydev->drv->phy_id != ATH8030_PHY_ID)
+		goto does_not_require_reset_workaround;
+
 	priv->gpiod_reset = devm_gpiod_get(dev, "reset");
 	if (IS_ERR(priv->gpiod_reset))
 		priv->gpiod_reset = NULL;
 	else
 		gpiod_direction_output(priv->gpiod_reset, 1);
 
+does_not_require_reset_workaround:
 	phydev->priv = priv;
 
 	return 0;