net: dsa: vsc73xx: use read_poll_timeout instead delay loop

Switch the delay loop during the Arbiter empty check from
vsc73xx_adjust_link() to use read_poll_timeout(). Functionally,
one msleep() call is eliminated at the end of the loop in the timeout
case.

As Russell King suggested:

"This [change] avoids the issue that on the last iteration, the code reads
the register, tests it, finds the condition that's being waiting for is
false, _then_ waits and end up printing the error message - that last
wait is rather useless, and as the arbiter state isn't checked after
waiting, it could be that we had success during the last wait."
Suggested-by: Russell King <linux@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Link: https://lore.kernel.org/r/20240417205048.3542839-2-paweldembicki@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/vitesse-vsc73xx-core.c

@@ -17,6 +17,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/iopoll.h>
 #include <linux/of.h>
 #include <linux/of_mdio.h>
 #include <linux/bitops.h>
@@ -268,6 +269,9 @@
 #define IS_7398(a) ((a)->chipid == VSC73XX_CHIPID_ID_7398)
 #define IS_739X(a) (IS_7395(a) || IS_7398(a))
 
+#define VSC73XX_POLL_SLEEP_US		1000
+#define VSC73XX_POLL_TIMEOUT_US		10000
+
 struct vsc73xx_counter {
 	u8 counter;
 	const char *name;
@@ -779,7 +783,7 @@ static void vsc73xx_adjust_link(struct dsa_switch *ds, int port,
 	 * after a PHY or the CPU port comes up or down.
 	 */
 	if (!phydev->link) {
-		int maxloop = 10;
+		int ret, err;
 
 		dev_dbg(vsc->dev, "port %d: went down\n",
 			port);
@@ -794,19 +798,17 @@ static void vsc73xx_adjust_link(struct dsa_switch *ds, int port,
 				    VSC73XX_ARBDISC, BIT(port), BIT(port));
 
 		/* Wait until queue is empty */
-		vsc73xx_read(vsc, VSC73XX_BLOCK_ARBITER, 0,
-			     VSC73XX_ARBEMPTY, &val);
-		while (!(val & BIT(port))) {
-			msleep(1);
-			vsc73xx_read(vsc, VSC73XX_BLOCK_ARBITER, 0,
-				     VSC73XX_ARBEMPTY, &val);
-			if (--maxloop == 0) {
-				dev_err(vsc->dev,
-					"timeout waiting for block arbiter\n");
-				/* Continue anyway */
-				break;
-			}
-		}
+		ret = read_poll_timeout(vsc73xx_read, err,
+					err < 0 || (val & BIT(port)),
+					VSC73XX_POLL_SLEEP_US,
+					VSC73XX_POLL_TIMEOUT_US, false,
+					vsc, VSC73XX_BLOCK_ARBITER, 0,
+					VSC73XX_ARBEMPTY, &val);
+		if (ret)
+			dev_err(vsc->dev,
+				"timeout waiting for block arbiter\n");
+		else if (err < 0)
+			dev_err(vsc->dev, "error reading arbiter\n");
 
 		/* Put this port into reset */
 		vsc73xx_write(vsc, VSC73XX_BLOCK_MAC, port, VSC73XX_MAC_CFG,