Subject: [PATCH] net: macb: reject unsupported rgmii delays

From: Helmut Grohne <[email-masked]>
Date: Tue, 16 Jun 2020 09:49:56 +0200

The macb driver does not support configuring rgmii delays. At least for
the Zynq GEM, delays are not supported by the hardware at all. However,
the driver happily accepts and ignores any such delays.

When operating in a mac to phy connection, the delay setting applies to
the phy. Since the MAC does not support delays, the phy must provide
them and the only supported mode is rgmii-id.  However, in a fixed mac
to mac connection, the delay applies to the mac itself. Therefore the
only supported rgmii mode is rgmii.

Link: https://lore.kernel.org/netdev/20200610081236.GA31659@laureti-dev/
Signed-off-by: Helmut Grohne <[email-masked]>
---
 drivers/net/ethernet/cadence/macb_main.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 5b9d7c60eebc..bee5bf65e8b3 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -514,7 +514,7 @@ static void macb_validate(struct phylink_config *config,
 	    state->interface != PHY_INTERFACE_MODE_RMII &&
 	    state->interface != PHY_INTERFACE_MODE_GMII &&
 	    state->interface != PHY_INTERFACE_MODE_SGMII &&
-	    !phy_interface_mode_is_rgmii(state->interface)) {
+	    state->interface != PHY_INTERFACE_MODE_RGMII_ID) {
 		bitmap_zero(supported, __ETHTOOL_LINK_MODE_MASK_NBITS);
 		return;
 	}
@@ -694,6 +694,13 @@ static int macb_phylink_connect(struct macb *bp)
 	struct phy_device *phydev;
 	int ret;
 
+	if (of_phy_is_fixed_link(dn) &&
+	    phy_interface_mode_is_rgmii(bp->phy_interface) &&
+	    bp->phy_interface != PHY_INTERFACE_MODE_RGMII) {
+		netdev_err(dev, "RGMII delays are not supported\n");
+		return -EINVAL;
+	}
+
 	if (dn)
 		ret = phylink_of_phy_connect(bp->phylink, dn, 0);
 
-- 
2.20.1