Date: Wed,  6 Sep 2023 12:59:04 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Andrew Lunn <andrew@...n.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Conor Dooley <conor+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Rob Herring <robh+dt@...nel.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com,
	"Russell King (Oracle)" <linux@...linux.org.uk>,
	devicetree@...r.kernel.org
Subject: [RFC net-next v2 2/2] net: dsa: microchip: Add drive strength configuration

Add device tree based drive strength configuration support. It is needed to
pass EMI validation on our hardware.

Configuration values are based on the vendor's reference driver.

Tested on KSZ9563R.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/net/dsa/microchip/ksz8795_reg.h |  14 --
 drivers/net/dsa/microchip/ksz9477_reg.h |  13 --
 drivers/net/dsa/microchip/ksz_common.c  | 286 ++++++++++++++++++++++++
 drivers/net/dsa/microchip/ksz_common.h  |  20 ++
 4 files changed, 306 insertions(+), 27 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz8795_reg.h b/drivers/net/dsa/microchip/ksz8795_reg.h
index 7a57c6088f809..d33db4f86c642 100644
--- a/drivers/net/dsa/microchip/ksz8795_reg.h
+++ b/drivers/net/dsa/microchip/ksz8795_reg.h
@@ -442,20 +442,6 @@
 #define TOS_PRIO_M			KS_PRIO_M
 #define TOS_PRIO_S			KS_PRIO_S
 
-#define REG_SW_CTRL_20			0xA3
-
-#define SW_GMII_DRIVE_STRENGTH_S	4
-#define SW_DRIVE_STRENGTH_M		0x7
-#define SW_DRIVE_STRENGTH_2MA		0
-#define SW_DRIVE_STRENGTH_4MA		1
-#define SW_DRIVE_STRENGTH_8MA		2
-#define SW_DRIVE_STRENGTH_12MA		3
-#define SW_DRIVE_STRENGTH_16MA		4
-#define SW_DRIVE_STRENGTH_20MA		5
-#define SW_DRIVE_STRENGTH_24MA		6
-#define SW_DRIVE_STRENGTH_28MA		7
-#define SW_MII_DRIVE_STRENGTH_S		0
-
 #define REG_SW_CTRL_21			0xA4
 
 #define SW_IPV6_MLD_OPTION		BIT(3)
diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index cba3dba58bc37..504e085aab522 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -112,19 +112,6 @@
 
 #define REG_SW_IBA_SYNC__1		0x010C
 
-#define REG_SW_IO_STRENGTH__1		0x010D
-#define SW_DRIVE_STRENGTH_M		0x7
-#define SW_DRIVE_STRENGTH_2MA		0
-#define SW_DRIVE_STRENGTH_4MA		1
-#define SW_DRIVE_STRENGTH_8MA		2
-#define SW_DRIVE_STRENGTH_12MA		3
-#define SW_DRIVE_STRENGTH_16MA		4
-#define SW_DRIVE_STRENGTH_20MA		5
-#define SW_DRIVE_STRENGTH_24MA		6
-#define SW_DRIVE_STRENGTH_28MA		7
-#define SW_HI_SPEED_DRIVE_STRENGTH_S	4
-#define SW_LO_SPEED_DRIVE_STRENGTH_S	0
-
 #define REG_SW_IBA_STATUS__4		0x0110
 
 #define SW_IBA_REQ			BIT(31)
diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 6673122266b7a..dd452ad94bc47 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -186,6 +186,60 @@ static const struct ksz_mib_names ksz9477_mib_names[] = {
 	{ 0x83, "tx_discards" },
 };
 
+struct ksz_driver_strength_prop {
+	const char *name;
+	int offset;
+	int value;
+};
+
+enum ksz_driver_strength_type {
+	KSZ_DRIVER_STRENGTH_HI,
+	KSZ_DRIVER_STRENGTH_LO,
+	KSZ_DRIVER_STRENGTH_IO,
+};
+
+/**
+ * struct ksz9477_drive_strength - drive strength mapping
+ * @reg_val:	register value
+ * @milliamp:	milliamp value
+ */
+struct ksz9477_drive_strength {
+	u32 reg_val;
+	u32 milliamp;
+};
+
+/* ksz9477_drive_strengths - Drive strength mapping for KSZ9477 variants
+ *
+ * This values are not documented in KSZ9477 variants.
+ * Documentation in KSZ8795CLX provides more information with some
+ * recommendations:
+ * - for high speed signals
+ *   1. 4 mA or 8 mA is often used for MII, RMII, and SPI interface with using
+ *      2.5V or 3.3V VDDIO.
+ *   2. 12 mA or 16 mA is often used for MII, RMII, and SPI interface with
+ *      using 1.8V VDDIO.
+ *   3. 20 mA or 24 mA is often used for GMII/RGMII interface with using 2.5V
+ *      or 3.3V VDDIO.
+ *   4. 28 mA is often used for GMII/RGMII interface with using 1.8V VDDIO.
+ *   5. In same interface, the heavy loading should use higher one of the
+ *      drive current strength.
+ * - for low speed signals
+ *   1. 3.3V VDDIO, use either 4 mA or 8 mA.
+ *   2. 2.5V VDDIO, use either 8 mA or 12 mA.
+ *   3. 1.8V VDDIO, use either 12 mA or 16 mA.
+ *   4. If it is heavy loading, can use higher drive current strength.
+ */
+static const struct ksz9477_drive_strength ksz9477_drive_strengths[] = {
+	{ SW_DRIVE_STRENGTH_2MA,  2000 },
+	{ SW_DRIVE_STRENGTH_4MA,  4000 },
+	{ SW_DRIVE_STRENGTH_8MA,  8000 },
+	{ SW_DRIVE_STRENGTH_12MA, 12000 },
+	{ SW_DRIVE_STRENGTH_16MA, 16000 },
+	{ SW_DRIVE_STRENGTH_20MA, 20000 },
+	{ SW_DRIVE_STRENGTH_24MA, 24000 },
+	{ SW_DRIVE_STRENGTH_28MA, 28000 },
+};
+
 static const struct ksz_dev_ops ksz8_dev_ops = {
 	.setup = ksz8_setup,
 	.get_port_addr = ksz8_get_port_addr,
@@ -3516,6 +3570,234 @@ static void ksz_parse_rgmii_delay(struct ksz_device *dev, int port_num,
 	dev->ports[port_num].rgmii_tx_val = tx_delay;
 }
 
+/**
+ * ksz9477_drive_strength_to_reg() - Convert drive strength value to
+ *				     corresponding register value for KSZ9477
+ *				     compatible switches.
+ * @milliamp: The drive strength value in milliamp to be converted.
+ *
+ * This function searches the predefined ksz9477_drive_strengths array for a
+ * match with the provided milliamp value.
+ *
+ * Returns: If found, the corresponding register value for that drive strength
+ * is returned. Otherwise, -EINVAL is returned indicating an invalid value.
+ */
+static int ksz9477_drive_strength_to_reg(int milliamp)
+{
+	size_t array_size = ARRAY_SIZE(ksz9477_drive_strengths);
+	int i;
+
+	for (i = 0; i < array_size; i++) {
+		if (ksz9477_drive_strengths[i].milliamp == milliamp)
+			return ksz9477_drive_strengths[i].reg_val;
+	}
+
+	return -EINVAL;
+}
+
+/**
+ * ksz9477_drive_strength_error() - Report invalid drive strength value for the
+ *				    KSZ9477 chip variants.
+ * @dev:       ksz device
+ * @milliamp:  Invalid drive strength value in milliamp
+ *
+ * This function logs an error message when an unsupported drive strength value
+ * is detected for a KSZ9477 chip variant. It lists out all the supported drive
+ * strength values for reference in the error message.
+ */
+static void ksz9477_drive_strength_error(struct ksz_device *dev, int milliamp)
+{
+	size_t array_size = ARRAY_SIZE(ksz9477_drive_strengths);
+	char supported_values[100];
+	int i;
+
+	for (i = 0; i < array_size; i++) {
+		if (i == 0)
+			snprintf(supported_values, sizeof(supported_values),
+				 "%d", ksz9477_drive_strengths[i].milliamp);
+		else
+			snprintf(supported_values, sizeof(supported_values),
+				 "%s, %d", supported_values,
+				 ksz9477_drive_strengths[i].milliamp);
+	}
+
+	dev_err(dev->dev, "Invalid drive strength %d, supported values are %s\n",
+		milliamp, supported_values);
+}
+
+/**
+ * ksz9477_drive_strength_write() - Set the drive strength for specific KSZ9477
+ *				    chip variants.
+ * @dev:       ksz device
+ * @props:     Array of drive strength properties to be applied
+ * @num_props: Number of properties in the array
+ *
+ * This function configures the drive strength for various KSZ9477 chip variants
+ * based on the provided properties. It handles chip-specific nuances and
+ * ensures only valid drive strengths are written to the respective chip.
+ *
+ * Return: 0 on successful configuration, a negative error code on failure.
+ */
+static int ksz9477_drive_strength_write(struct ksz_device *dev,
+					struct ksz_driver_strength_prop *props,
+					int num_props)
+{
+	int i, ret, reg;
+	u8 val;
+
+	if (props[KSZ_DRIVER_STRENGTH_IO].value != -1)
+		dev_warn(dev->dev, "%s is not supported by this chip variant\n",
+			 props[KSZ_DRIVER_STRENGTH_IO].name);
+
+	if (dev->chip_id == KSZ8795_CHIP_ID ||
+	    dev->chip_id == KSZ8794_CHIP_ID ||
+	    dev->chip_id == KSZ8765_CHIP_ID)
+		reg = KSZ8795_REG_SW_CTRL_20;
+	else
+		reg = KSZ9477_REG_SW_IO_STRENGTH;
+
+	ret = ksz_read8(dev, reg, &val);
+	if (ret)
+		return ret;
+
+	for (i = 0; i < num_props; i++) {
+		if (props[i].value == -1)
+			continue;
+
+		ret = ksz9477_drive_strength_to_reg(props[i].value);
+		if (ret < 0) {
+			ksz9477_drive_strength_error(dev, props[i].value);
+			return ret;
+		}
+
+		val &= ~(SW_DRIVE_STRENGTH_M << props[i].offset);
+		val |= ret << props[i].offset;
+	}
+
+	return ksz_write8(dev, reg, val);
+}
+
+/**
+ * ksz8830_drive_strength_write() - Set the drive strength configuration for
+ *				    KSZ8830 compatible chip variants.
+ * @dev:       ksz device
+ * @props:     Array of drive strength properties to be set
+ * @num_props: Number of properties in the array
+ *
+ * This function applies the specified drive strength settings to KSZ8830 chip
+ * variants (KSZ8873, KSZ8863).
+ * It ensures the configurations align with what the chip variant supports and
+ * warns or errors out on unsupported settings.
+ *
+ * Return: 0 on success, error code otherwise
+ */
+static int ksz8830_drive_strength_write(struct ksz_device *dev,
+					struct ksz_driver_strength_prop *props,
+					int num_props)
+{
+	u8 val;
+	int i;
+
+	for (i = 0; i < num_props; i++) {
+		if (props[i].value == -1 || i == KSZ_DRIVER_STRENGTH_IO)
+			continue;
+
+		dev_warn(dev->dev, "%s is not supported by this chip variant\n",
+			 props[i].name);
+	}
+
+	if (props[KSZ_DRIVER_STRENGTH_IO].value == 16000) {
+		val = KSZ8873_DRIVE_STRENGTH_16MA;
+	} else if (props[KSZ_DRIVER_STRENGTH_IO].value == 8000) {
+		val = 0;
+	} else {
+		dev_err(dev->dev, "Invalid drive strength %d, supported values are: 16000, 8000\n",
+			props[KSZ_DRIVER_STRENGTH_IO].value);
+		return -EINVAL;
+	}
+
+	return ksz_rmw8(dev, KSZ8873_REG_GLOBAL_CTRL_12,
+			KSZ8873_DRIVE_STRENGTH_16MA, val);
+}
+
+/**
+ * ksz_parse_drive_strength() - Extract and apply drive strength configurations
+ *				from device tree properties.
+ * @dev:	ksz device
+ *
+ * This function reads the specified drive strength properties from the
+ * device tree, validates against the supported chip variants, and sets
+ * them accordingly.
+ *
+ * Return: 0 on success, error code otherwise
+ */
+static int ksz_parse_drive_strength(struct ksz_device *dev)
+{
+	struct ksz_driver_strength_prop of_props[] = {
+		[KSZ_DRIVER_STRENGTH_HI] = {
+			.name = "microchip,hi-drive-strength-microamp",
+			.offset = SW_HI_SPEED_DRIVE_STRENGTH_S,
+			.value = -1
+		},
+		[KSZ_DRIVER_STRENGTH_LO] = {
+			.name = "microchip,lo-drive-strength-microamp",
+			.offset = SW_LO_SPEED_DRIVE_STRENGTH_S,
+			.value = -1
+		},
+		[KSZ_DRIVER_STRENGTH_IO] = {
+			.name = "microchip,io-drive-strength-microamp",
+			.offset = 0, /* don't care */
+			.value = -1
+		},
+	};
+	struct device_node *np = dev->dev->of_node;
+	bool found = false;
+	int i, ret;
+
+	for (i = 0; i < ARRAY_SIZE(of_props); i++) {
+		ret = of_property_read_u32(np, of_props[i].name,
+					   &of_props[i].value);
+		if (ret && ret != -EINVAL)
+			dev_warn(dev->dev, "Failed to read %s\n",
+				 of_props[i].name);
+		if (ret)
+			continue;
+
+		found = true;
+	}
+
+	if (!found)
+		return 0;
+
+	switch (dev->chip_id) {
+	case KSZ8830_CHIP_ID:
+		return ksz8830_drive_strength_write(dev, of_props,
+						    ARRAY_SIZE(of_props));
+	case KSZ8795_CHIP_ID:
+	case KSZ8794_CHIP_ID:
+	case KSZ8765_CHIP_ID:
+	case KSZ8563_CHIP_ID:
+	case KSZ9477_CHIP_ID:
+	case KSZ9563_CHIP_ID:
+	case KSZ9567_CHIP_ID:
+	case KSZ9893_CHIP_ID:
+	case KSZ9896_CHIP_ID:
+	case KSZ9897_CHIP_ID:
+		return ksz9477_drive_strength_write(dev, of_props,
+						    ARRAY_SIZE(of_props));
+	default:
+		for (i = 0; i < ARRAY_SIZE(of_props); i++) {
+			if (of_props[i].value == -1)
+				continue;
+
+			dev_warn(dev->dev, "%s is not supported by this chip variant\n",
+				 of_props[i].name);
+		}
+	}
+
+	return 0;
+}
+
 int ksz_switch_register(struct ksz_device *dev)
 {
 	const struct ksz_chip_data *info;
@@ -3598,6 +3880,10 @@ int ksz_switch_register(struct ksz_device *dev)
 	for (port_num = 0; port_num < dev->info->port_cnt; ++port_num)
 		dev->ports[port_num].interface = PHY_INTERFACE_MODE_NA;
 	if (dev->dev->of_node) {
+		ret = ksz_parse_drive_strength(dev);
+		if (ret)
+			return ret;
+
 		ret = of_get_phy_mode(dev->dev->of_node, &interface);
 		if (ret == 0)
 			dev->compat_interface = interface;
diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index a4de58847deab..ca37b5b879464 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -689,6 +689,26 @@ static inline int is_lan937x(struct ksz_device *dev)
 #define KSZ8_LEGAL_PACKET_SIZE		1518
 #define KSZ9477_MAX_FRAME_SIZE		9000
 
+#define KSZ8873_REG_GLOBAL_CTRL_12	0x0e
+/* Drive Strength of I/O Pad
+ * 0: 8mA, 1: 16mA
+ */
+#define KSZ8873_DRIVE_STRENGTH_16MA	BIT(6)
+
+#define KSZ8795_REG_SW_CTRL_20		0xa3
+#define KSZ9477_REG_SW_IO_STRENGTH	0x010d
+#define SW_DRIVE_STRENGTH_M		0x7
+#define SW_DRIVE_STRENGTH_2MA		0
+#define SW_DRIVE_STRENGTH_4MA		1
+#define SW_DRIVE_STRENGTH_8MA		2
+#define SW_DRIVE_STRENGTH_12MA		3
+#define SW_DRIVE_STRENGTH_16MA		4
+#define SW_DRIVE_STRENGTH_20MA		5
+#define SW_DRIVE_STRENGTH_24MA		6
+#define SW_DRIVE_STRENGTH_28MA		7
+#define SW_HI_SPEED_DRIVE_STRENGTH_S	4
+#define SW_LO_SPEED_DRIVE_STRENGTH_S	0
+
 #define KSZ9477_REG_PORT_OUT_RATE_0	0x0420
 #define KSZ9477_OUT_RATE_NO_LIMIT	0
 
-- 
2.39.2

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