drivers: ethernet: ksz8081: Fix reset times

500 ms reset time is only for software reset and comes from IEEE spec.
Datasheet mentions for hardware reset the assertion of the signal should
only need to be 500 us, and 100 us after deassert to wait to access
programming interface.

Also remove an unused macro.

Signed-off-by: Declan Snyder <[email protected]>

Author: decsny

drivers/ethernet/phy/phy_microchip_ksz8081.c

@@ -30,8 +30,6 @@ LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 #define PHY_MC_KSZ8081_CTRL2_REG		0x1F
 #define PHY_MC_KSZ8081_CTRL2_REF_CLK_SEL	BIT(7)
 
-#define PHY_MC_KSZ8081_RESET_HOLD_TIME
-
 enum ksz8081_interface {
 	KSZ8081_MII,
 	KSZ8081_RMII,
@@ -289,20 +287,27 @@ static int phy_mc_ksz8081_reset(const struct device *dev)
 		goto done;
 	}
 
-	/* Wait for 500 ms as specified by datasheet */
-	k_busy_wait(USEC_PER_MSEC * 500);
+	/* Wait for at least 500 us as specified by datasheet */
+	k_busy_wait(1000);
 
 	/* Reset over */
 	ret = gpio_pin_set_dt(&config->reset_gpio, 1);
+
+	/* After deasserting reset, must wait at least 100 us to use programming interface */
+	k_busy_wait(200);
+
 	goto done;
 skip_reset_gpio:
 #endif /* DT_ANY_INST_HAS_PROP_STATUS_OKAY(reset_gpios) */
 	ret = phy_mc_ksz8081_write(dev, MII_BMCR, MII_BMCR_RESET);
 	if (ret) {
 		goto done;
 	}
-	/* Wait for 500 ms as specified by datasheet */
-	k_busy_wait(USEC_PER_MSEC * 500);
+
+	/* According to IEEE 802.3, Section 2, Subsection 22.2.4.1.1,
+	 * a PHY reset may take up to 0.5 s.
+	 */
+	k_busy_wait(500 * USEC_PER_MSEC);
 
 done:
 	/* Unlock mutex */