[PATCH net-next 6/9] net: dsa: vsc73xx: speed up mdio bus to max allowed value

[Pawel Dembicki <paweldembicki@gmail.com>]

According the datasheet, vsc73xx family max internal mdio bus speed is
20MHz. It also allow to disable preamble.

This commit sets mdio clock prescaler to minimal value and crop preamble
to speed up mdio operations.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
---
 drivers/net/dsa/vitesse-vsc73xx-core.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/net/dsa/vitesse-vsc73xx-core.c b/drivers/net/dsa/vitesse-vsc73xx-core.c
index 40c64ef7e729..9e88eda6f4dd 100644
--- a/drivers/net/dsa/vitesse-vsc73xx-core.c
+++ b/drivers/net/dsa/vitesse-vsc73xx-core.c
@@ -229,6 +229,7 @@
 #define VSC73XX_MII_STAT		0x0
 #define VSC73XX_MII_CMD			0x1
 #define VSC73XX_MII_DATA		0x2
+#define VSC73XX_MII_MPRES		0x3
 
 #define VSC73XX_MII_STAT_BUSY		BIT(3)
 #define VSC73XX_MII_STAT_READ		BIT(2)
@@ -243,6 +244,10 @@
 #define VSC73XX_MII_DATA_FAILURE	BIT(16)
 #define VSC73XX_MII_DATA_READ_DATA	GENMASK(15, 0)
 
+#define VSC73XX_MII_MPRES_NOPREAMBLE	BIT(6)
+#define VSC73XX_MII_MPRES_PRESCALEVAL	GENMASK(5, 0)
+#define VSC73XX_MII_PRESCALEVAL_MIN	3 /* min allowed mdio clock prescaler */
+
 /* Arbiter block 5 registers */
 #define VSC73XX_ARBEMPTY		0x0c
 #define VSC73XX_ARBDISC			0x0e
@@ -578,7 +583,7 @@ static int vsc73xx_phy_read(struct dsa_switch *ds, int phy, int regnum)
 			    VSC73XX_MII_CMD, cmd);
 	if (ret)
 		goto err;
-	usleep_range(100, 200);
+	usleep_range(4, 100);
 	ret = vsc73xx_read(vsc, VSC73XX_BLOCK_MII, VSC73XX_BLOCK_MII_INTERNAL,
 			   VSC73XX_MII_DATA, &val);
 	if (ret)
@@ -632,7 +637,7 @@ static int vsc73xx_phy_write(struct dsa_switch *ds, int phy, int regnum,
 	if (!ret)
 		dev_dbg(vsc->dev, "write %04x to reg %02x in phy%d\n",
 			val, regnum, phy);
-	usleep_range(100, 200);
+	usleep_range(4, 100);
 err:
 	mutex_unlock(&vsc->mdio_lock);
 	return ret;
@@ -802,7 +807,7 @@ static int vsc73xx_configure_rgmii_port_delay(struct dsa_switch *ds)
 static int vsc73xx_setup(struct dsa_switch *ds)
 {
 	struct vsc73xx *vsc = ds->priv;
-	int i, ret;
+	int i, ret, val;
 
 	dev_info(vsc->dev, "set up the switch\n");
 
@@ -875,6 +880,15 @@ static int vsc73xx_setup(struct dsa_switch *ds)
 
 	mdelay(50);
 
+	/* Disable preamble and use maximum allowed clock for the internal
+	 * mdio bus, used for communication with internal PHYs only.
+	 */
+	val = VSC73XX_MII_MPRES_NOPREAMBLE |
+	      FIELD_PREP(VSC73XX_MII_MPRES_PRESCALEVAL,
+			 VSC73XX_MII_PRESCALEVAL_MIN);
+	vsc73xx_write(vsc, VSC73XX_BLOCK_MII, VSC73XX_BLOCK_MII_INTERNAL,
+		      VSC73XX_MII_MPRES, val);
+
 	/* Release reset from the internal PHYs */
 	vsc73xx_write(vsc, VSC73XX_BLOCK_SYSTEM, 0, VSC73XX_GLORESET,
 		      VSC73XX_GLORESET_PHY_RESET);
-- 
2.34.1