From: David Rivshin <redacted>

The cpsw-phy-sel driver supports only MII, RMII, and RGMII PHY modes,
and silently handled any other values as if MII was specified. In a
case where the PHY mode was incorrectly specified, or a bug elsewhere,
there would be no indication of a problem. If MII was the correct mode,
then this will go unnoticed, otherwise the symptom will be a failure
to transmit/receive data over the RMII/RGMII link.

Add a dev_warn() to make this condition obvious and provide a
breadcrumb to follow.

Cc: Mugunthan V N <redacted>
Signed-off-by: David Rivshin <redacted>
---

Dave,
 I'm not sure if you'd consider this net or net-next material, but it will
apply cleanly to either. Indeed, if you want it for -stable, it applies back
as far as 3.18.

 drivers/net/ethernet/ti/cpsw-phy-sel.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/ti/cpsw-phy-sel.c b/drivers/net/ethernet/ti/cpsw-phy-sel.c
index e9cc61e..c3e85ac 100644
--- a/drivers/net/ethernet/ti/cpsw-phy-sel.c
+++ b/drivers/net/ethernet/ti/cpsw-phy-sel.c

@@ -63,8 +63,12 @@ static void cpsw_gmii_sel_am3352(struct cpsw_phy_sel_priv *priv,
 		mode = AM33XX_GMII_SEL_MODE_RGMII;
 		break;
 
-	case PHY_INTERFACE_MODE_MII:
 	default:
+		dev_warn(priv->dev,
+			 "Unsupported PHY mode: \"%s\". Defaulting to MII.\n",
+			phy_modes(phy_mode));
+		/* fallthrough */
+	case PHY_INTERFACE_MODE_MII:
 		mode = AM33XX_GMII_SEL_MODE_MII;
 		break;
 	};

@@ -106,8 +110,12 @@ static void cpsw_gmii_sel_dra7xx(struct cpsw_phy_sel_priv *priv,
 		mode = AM33XX_GMII_SEL_MODE_RGMII;
 		break;
 
-	case PHY_INTERFACE_MODE_MII:
 	default:
+		dev_warn(priv->dev,
+			 "Unsupported PHY mode: \"%s\". Defaulting to MII.\n",
+			phy_modes(phy_mode));
+		/* fallthrough */
+	case PHY_INTERFACE_MODE_MII:
 		mode = AM33XX_GMII_SEL_MODE_MII;
 		break;
 	};

-- 
2.5.0