Add support for single LED mode via the "microchip,single-led-mode"
device tree property which will apply the configuration globally on all
non-CPU ports.

The implementation includes a workaround for Errata Module 19,
requiring a debug register write to ensure proper LED activity.
The mode is configured during the MAC link-up phase for non-CPU ports.

Signed-off-by: Heinrich Toews <ht@twx-software.de>
---
 drivers/net/dsa/microchip/ksz_common.c | 34 ++++++++++++++++++++++++++
 drivers/net/dsa/microchip/ksz_common.h |  4 +++
 2 files changed, 38 insertions(+)

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index e5fa1f5fc09b3..bef8ec51d9483 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -815,6 +815,9 @@ static const u16 ksz9477_regs[] = {
 	[PTP_RTC_SEC]			= 0x0508,
 	[PTP_SUBNANOSEC_RATE]		= 0x050C,
 	[PTP_MSG_CONF1]			= 0x0514,
+	[P_PHY_MMD_SETUP]		= 0x011A,
+	[P_PHY_MMD_DATA]		= 0x011C,
+	[P_PHY_DIGITAL_DEBUG_3]		= 0x013C,
 };
 
 static const u32 ksz9477_masks[] = {
@@ -3241,6 +3244,14 @@ static u32 ksz_get_phy_flags(struct dsa_switch *ds, int port)
 		if (!port)
 			return MICREL_KSZ8_P1_ERRATA;
 		break;
+	case KSZ9477_CHIP_ID:
+		/* KSZ9477S Errata DS80000754F
+		 *
+		 * Module 19: Single-LED Mode Setting Requires Two Register Writes
+		 *   The PHY Port LEDx_0 pin does not go low in the presence of link
+		 *   activity when Single-LED Mode is selected in the MMD LED Mode Register.
+		 */
+		return MICREL_KSZ9_LED_ERRATA;
 	}
 
 	return 0;
@@ -3909,6 +3920,24 @@ static void ksz_set_gbit(struct ksz_device *dev, int port, bool gbit)
 	ksz_pwrite8(dev, port, regs[P_XMII_CTRL_1], data8);
 }
 
+static void ksz_enable_single_led_mode(struct ksz_device *dev, int port, struct phy_device *phydev)
+{
+	const u16 *regs = dev->info->regs;
+
+	ksz_pwrite16(dev, port, regs[P_PHY_MMD_SETUP], 0x0002); /* Set up register address for MMD */
+	ksz_pwrite16(dev, port,  regs[P_PHY_MMD_DATA], 0x0000); /* Select Register 00h of MMD */
+	ksz_pwrite16(dev, port, regs[P_PHY_MMD_SETUP], 0x4002); /* Select register data for MMD */
+	ksz_pwrite16(dev, port,  regs[P_PHY_MMD_DATA], 0x0011); /* Write value 0011h to MMD */
+
+	/* According to KSZ9477S Errata DS80000754F (Module 19) 0xfa00 has to
+	 * be written to the Debug Register 3 to enable Single-LED Mode.
+	 */
+	if (phydev->dev_flags & MICREL_KSZ9_LED_ERRATA)
+		ksz_pwrite16(dev, port, regs[P_PHY_DIGITAL_DEBUG_3], 0xfa00);
+
+	dev_info(dev->dev, "port-%d: single-led mode enabled.\n", port);
+}
+
 static void ksz_set_100_10mbit(struct ksz_device *dev, int port, int speed)
 {
 	const u8 *bitval = dev->info->xmii_ctrl0;
@@ -3977,6 +4006,9 @@ static void ksz9477_phylink_mac_link_up(struct phylink_config *config,
 	int port = dp->index;
 	struct ksz_port *p;
 
+	if (dev->single_led_mode && port != dev->cpu_port)
+		ksz_enable_single_led_mode(dev, port, phydev);
+
 	p = &dev->ports[port];
 
 	/* Internal PHYs */
@@ -5526,6 +5558,8 @@ int ksz_switch_register(struct ksz_device *dev)
 							   "wakeup-source");
 		dev->pme_active_high = of_property_read_bool(dev->dev->of_node,
 							     "microchip,pme-active-high");
+		dev->single_led_mode = of_property_read_bool(dev->dev->of_node,
+							     "microchip,single-led-mode");
 	}
 
 	ret = dsa_register_switch(dev->ds);
diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index 929aff4c55de5..9900e9dd91810 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -187,6 +187,7 @@ struct ksz_device {
 	bool synclko_disable;
 	bool wakeup_source;
 	bool pme_active_high;
+	bool single_led_mode;		/* Enable Single LED Mode */
 
 	struct vlan_table *vlan_cache;
 
@@ -277,6 +278,9 @@ enum ksz_regs {
 	PTP_RTC_SUB_NANOSEC,
 	PTP_SUBNANOSEC_RATE,
 	PTP_MSG_CONF1,
+	P_PHY_MMD_SETUP,
+	P_PHY_MMD_DATA,
+	P_PHY_DIGITAL_DEBUG_3,
 };
 
 enum ksz_masks {
-- 
2.52.0