From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Support newly introduced maxlinear,mii-slew-rate-slow device tree property
to configure R(G)MII interface pins slew rate into "slow" mode. It might be
used to reduce the radiated emissions.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
 drivers/net/dsa/lantiq/mxl-gsw1xx.c | 6 ++++++
 drivers/net/dsa/lantiq/mxl-gsw1xx.h | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/drivers/net/dsa/lantiq/mxl-gsw1xx.c b/drivers/net/dsa/lantiq/mxl-gsw1xx.c
index 0816c61a47f12..ec7b92f62dcb5 100644
--- a/drivers/net/dsa/lantiq/mxl-gsw1xx.c
+++ b/drivers/net/dsa/lantiq/mxl-gsw1xx.c
@@ -526,6 +526,12 @@ static struct phylink_pcs *gsw1xx_phylink_mac_select_pcs(struct phylink_config *
 	switch (dp->index) {
 	case GSW1XX_SGMII_PORT:
 		return &gsw1xx_priv->pcs;
+	case GSW1XX_MII_PORT:
+		if (of_property_read_bool(dp->dn, "maxlinear,mii-slew-rate-slow"))
+			regmap_set_bits(gsw1xx_priv->shell,
+					RGMII_SLEW_CFG_DRV_TXD | RGMII_SLEW_CFG_DRV_TXC,
+					GSW1XX_SHELL_RGMII_SLEW_CFG);
+		return NULL;
 	default:
 		return NULL;
 	}
diff --git a/drivers/net/dsa/lantiq/mxl-gsw1xx.h b/drivers/net/dsa/lantiq/mxl-gsw1xx.h
index 38e03c048a26c..8c0298b2b7663 100644
--- a/drivers/net/dsa/lantiq/mxl-gsw1xx.h
+++ b/drivers/net/dsa/lantiq/mxl-gsw1xx.h
@@ -110,6 +110,8 @@
 #define   GSW1XX_RST_REQ_SGMII_SHELL		BIT(5)
 /* RGMII PAD Slew Control Register */
 #define  GSW1XX_SHELL_RGMII_SLEW_CFG		0x78
+#define   RGMII_SLEW_CFG_DRV_TXC		BIT(2)
+#define   RGMII_SLEW_CFG_DRV_TXD		BIT(3)
 #define   RGMII_SLEW_CFG_RX_2_5_V		BIT(4)
 #define   RGMII_SLEW_CFG_TX_2_5_V		BIT(5)
 
-- 
2.52.0

> +	case GSW1XX_MII_PORT:
> +		if (of_property_read_bool(dp->dn, "maxlinear,mii-slew-rate-slow"))
> +			regmap_set_bits(gsw1xx_priv->shell,
> +					RGMII_SLEW_CFG_DRV_TXD | RGMII_SLEW_CFG_DRV_TXC,
> +					GSW1XX_SHELL_RGMII_SLEW_CFG);

The binding says:

+              Configure R(G)MII TXD/TXC pads' slew rate to "slow" instead
+              of "normal" to reduce radiated emissions.

So you really should set the slew to normal if the property does not
exist.

	Andrew