phy: micrel: ksz8041nl: do not use power down mode

Some Micrel KSZ8041NL PHY chips exhibit continuous RX errors after using
the power down mode bit (0.11). If the PHY is taken out of power down
mode in a certain temperature range, the PHY enters a weird state which
leads to continuously reporting RX errors. In that state, the MAC is not
able to receive or send any Ethernet frames and the activity LED is
constantly blinking. Since Linux is using the suspend callback when the
interface is taken down, ending up in that state can easily happen
during a normal startup.

Micrel confirmed the issue in errata DS80000700A [*], caused by abnormal
clock recovery when using power down mode. Even the latest revision (A4,
Revision ID 0x1513) seems to suffer that problem, and according to the
errata is not going to be fixed.

Remove the suspend/resume callback to avoid using the power down mode
completely.

[*] https://ww1.microchip.com/downloads/en/DeviceDoc/80000700A.pdf

Fixes: 1a5465f5d6 ("phy/micrel: Add suspend/resume support to Micrel PHYs")
Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/micrel.c

@@ -1676,8 +1676,9 @@ static struct phy_driver ksphy_driver[] = {
 	.get_sset_count = kszphy_get_sset_count,
 	.get_strings	= kszphy_get_strings,
 	.get_stats	= kszphy_get_stats,
-	.suspend	= genphy_suspend,
-	.resume		= genphy_resume,
+	/* No suspend/resume callbacks because of errata DS80000700A,
+	 * receiver error following software power down.
+	 */
 }, {
 	.phy_id		= PHY_ID_KSZ8041RNLI,
 	.phy_id_mask	= MICREL_PHY_ID_MASK,