[PATCH net v3 3/5] net: dsa: vsc73xx: check busy flag in MDIO operations

[Pawel Dembicki <paweldembicki@gmail.com>]

The VSC73xx has a busy flag used during MDIO operations. It is raised
when MDIO read/write operations are in progress. Without it, PHYs are
misconfigured and bus operations do not work as expected.

Fixes: 05bd97fc559d ("net: dsa: Add Vitesse VSC73xx DSA router driver")
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>

---
v3:
  - removed blank line and unnecessary variable init
v2:
  - used defines from patch moved to net-next

This patch came from net-next series[0].
Changes since net-next:
  - removed mutex
  - used method poll.h to poll busy value in 'vsc73xx_mdio_busy_check'
  - use 'vsc73xx_mdio_busy_check' for control if mdio is ready

[0] https://patchwork.kernel.org/project/netdevbpf/patch/20240729210615.279952-6-paweldembicki@gmail.com/
---
 drivers/net/dsa/vitesse-vsc73xx-core.c | 37 +++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/vitesse-vsc73xx-core.c b/drivers/net/dsa/vitesse-vsc73xx-core.c
index 4b300c293dec..a789b2da9b7d 100644
--- a/drivers/net/dsa/vitesse-vsc73xx-core.c
+++ b/drivers/net/dsa/vitesse-vsc73xx-core.c
@@ -40,6 +40,10 @@
 #define VSC73XX_BLOCK_ARBITER	0x5 /* Only subblock 0 */
 #define VSC73XX_BLOCK_SYSTEM	0x7 /* Only subblock 0 */
 
+/* MII Block subblock */
+#define VSC73XX_BLOCK_MII_INTERNAL	0x0 /* Internal MDIO subblock */
+#define VSC73XX_BLOCK_MII_EXTERNAL	0x1 /* External MDIO subblock */
+
 #define CPU_PORT	6 /* CPU port */
 
 /* MAC Block registers */
@@ -225,6 +229,8 @@
 #define VSC73XX_MII_CMD		0x1
 #define VSC73XX_MII_DATA	0x2
 
+#define VSC73XX_MII_STAT_BUSY	BIT(3)
+
 /* Arbiter block 5 registers */
 #define VSC73XX_ARBEMPTY		0x0c
 #define VSC73XX_ARBDISC			0x0e
@@ -299,6 +305,7 @@
 #define IS_739X(a) (IS_7395(a) || IS_7398(a))
 
 #define VSC73XX_POLL_SLEEP_US		1000
+#define VSC73XX_MDIO_POLL_SLEEP_US	5
 #define VSC73XX_POLL_TIMEOUT_US		10000
 
 struct vsc73xx_counter {
@@ -527,6 +534,22 @@ static int vsc73xx_detect(struct vsc73xx *vsc)
 	return 0;
 }
 
+static int vsc73xx_mdio_busy_check(struct vsc73xx *vsc)
+{
+	int ret, err;
+	u32 val;
+
+	ret = read_poll_timeout(vsc73xx_read, err,
+				err < 0 || !(val & VSC73XX_MII_STAT_BUSY),
+				VSC73XX_MDIO_POLL_SLEEP_US,
+				VSC73XX_POLL_TIMEOUT_US, false, vsc,
+				VSC73XX_BLOCK_MII, VSC73XX_BLOCK_MII_INTERNAL,
+				VSC73XX_MII_STAT, &val);
+	if (ret)
+		return ret;
+	return err;
+}
+
 static int vsc73xx_phy_read(struct dsa_switch *ds, int phy, int regnum)
 {
 	struct vsc73xx *vsc = ds->priv;
@@ -534,12 +557,20 @@ static int vsc73xx_phy_read(struct dsa_switch *ds, int phy, int regnum)
 	u32 val;
 	int ret;
 
+	ret = vsc73xx_mdio_busy_check(vsc);
+	if (ret)
+		return ret;
+
 	/* Setting bit 26 means "read" */
 	cmd = BIT(26) | (phy << 21) | (regnum << 16);
 	ret = vsc73xx_write(vsc, VSC73XX_BLOCK_MII, 0, 1, cmd);
 	if (ret)
 		return ret;
-	msleep(2);
+
+	ret = vsc73xx_mdio_busy_check(vsc);
+	if (ret)
+		return ret;
+
 	ret = vsc73xx_read(vsc, VSC73XX_BLOCK_MII, 0, 2, &val);
 	if (ret)
 		return ret;
@@ -563,6 +594,10 @@ static int vsc73xx_phy_write(struct dsa_switch *ds, int phy, int regnum,
 	u32 cmd;
 	int ret;
 
+	ret = vsc73xx_mdio_busy_check(vsc);
+	if (ret)
+		return ret;
+
 	/* It was found through tedious experiments that this router
 	 * chip really hates to have it's PHYs reset. They
 	 * never recover if that happens: autonegotiation stops
-- 
2.34.1