Revert "dsa: mv88e6xxx: make serdes SGMII/Fiber tx amplitude configurable"

This reverts commit 926eae604403acfa27ba5b072af458e87e634a50, which
never could have produced the intended effect:
https://lore.kernel.org/netdev/[e-mail]/

The reason why it is broken beyond repair in this form is that the
mv88e6xxx driver outsources its "tx-p2p-microvolt" property to the OF
node of an external Ethernet PHY. This:
(a) does not work if there is no external PHY (chip-to-chip connection,
or SFP module)
(b) pollutes the OF property namespace / bindings of said external PHY
("tx-p2p-microvolt" could have meaning for the Ethernet PHY's SerDes
interface as well)

We can revisit the idea of making SerDes amplitude configurable once we
have proper bindings for the mv88e6xxx SerDes. Until then, remove the
code that leaves us with unnecessary baggage.

Fixes: 926eae604403 ("dsa: mv88e6xxx: make serdes SGMII/Fiber tx amplitude configurable")
Cc: Holger Brunck <[e-mail]>
Signed-off-by: Vladimir Oltean <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/dsa/mv88e6xxx/chip.c

···
 
 static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 {
-	struct device_node *phy_handle = NULL;
 	struct fwnode_handle *ports_fwnode;
 	struct fwnode_handle *port_fwnode;
 	struct dsa_switch *ds = chip->ds;
 	struct mv88e6xxx_port *p;
-	struct dsa_port *dp;
-	int tx_amp;
 	int err;
 	u16 reg;
 	u32 val;
···
 		err = chip->info->ops->port_setup_message_port(chip, port);
 		if (err)
 			return err;
-	}
-
-	if (chip->info->ops->serdes_set_tx_amplitude) {
-		dp = dsa_to_port(ds, port);
-		if (dp)
-			phy_handle = of_parse_phandle(dp->dn, "phy-handle", 0);
-
-		if (phy_handle && !of_property_read_u32(phy_handle,
-							"tx-p2p-microvolt",
-							&tx_amp))
-			err = chip->info->ops->serdes_set_tx_amplitude(chip,
-								port, tx_amp);
-		if (phy_handle) {
-			of_node_put(phy_handle);
-			if (err)
-				return err;
-		}
 	}
 
 	/* Port based VLAN map: give each port the same default address
···
 	.serdes_irq_mapping = mv88e6352_serdes_irq_mapping,
 	.serdes_get_regs_len = mv88e6352_serdes_get_regs_len,
 	.serdes_get_regs = mv88e6352_serdes_get_regs,
-	.serdes_set_tx_amplitude = mv88e6352_serdes_set_tx_amplitude,
 	.gpio_ops = &mv88e6352_gpio_ops,
 	.phylink_get_caps = mv88e6352_phylink_get_caps,
 	.pcs_ops = &mv88e6352_pcs_ops,
···
 	.serdes_irq_mapping = mv88e6352_serdes_irq_mapping,
 	.serdes_get_regs_len = mv88e6352_serdes_get_regs_len,
 	.serdes_get_regs = mv88e6352_serdes_get_regs,
-	.serdes_set_tx_amplitude = mv88e6352_serdes_set_tx_amplitude,
 	.gpio_ops = &mv88e6352_gpio_ops,
 	.avb_ops = &mv88e6352_avb_ops,
 	.ptp_ops = &mv88e6352_ptp_ops,
···
 	.serdes_get_stats = mv88e6352_serdes_get_stats,
 	.serdes_get_regs_len = mv88e6352_serdes_get_regs_len,
 	.serdes_get_regs = mv88e6352_serdes_get_regs,
-	.serdes_set_tx_amplitude = mv88e6352_serdes_set_tx_amplitude,
 	.phylink_get_caps = mv88e6352_phylink_get_caps,
 	.pcs_ops = &mv88e6352_pcs_ops,
 };

drivers/net/dsa/mv88e6xxx/chip.h

···
 	void (*serdes_get_regs)(struct mv88e6xxx_chip *chip, int port,
 				void *_p);
 
-	/* SERDES SGMII/Fiber Output Amplitude */
-	int (*serdes_set_tx_amplitude)(struct mv88e6xxx_chip *chip, int port,
-				       int val);
-
 	/* Address Translation Unit operations */
 	int (*atu_get_hash)(struct mv88e6xxx_chip *chip, u8 *hash);
 	int (*atu_set_hash)(struct mv88e6xxx_chip *chip, u8 hash);

drivers/net/dsa/mv88e6xxx/serdes.c

···
 				       reg, val);
 }
 
-static int mv88e6352_serdes_write(struct mv88e6xxx_chip *chip, int reg,
-				  u16 val)
-{
-	return mv88e6xxx_phy_page_write(chip, MV88E6352_ADDR_SERDES,
-					MV88E6352_SERDES_PAGE_FIBER,
-					reg, val);
-}
-
 static int mv88e6390_serdes_read(struct mv88e6xxx_chip *chip,
 				 int lane, int device, int reg, u16 *val)
 {
···
 		if (!err)
 			p[i] = reg;
 	}
-}
-
-static const int mv88e6352_serdes_p2p_to_reg[] = {
-	/* Index of value in microvolts corresponds to the register value */
-	14000, 112000, 210000, 308000, 406000, 504000, 602000, 700000,
-};
-
-int mv88e6352_serdes_set_tx_amplitude(struct mv88e6xxx_chip *chip, int port,
-				      int val)
-{
-	bool found = false;
-	u16 ctrl, reg;
-	int err;
-	int i;
-
-	err = mv88e6352_g2_scratch_port_has_serdes(chip, port);
-	if (err <= 0)
-		return err;
-
-	for (i = 0; i < ARRAY_SIZE(mv88e6352_serdes_p2p_to_reg); ++i) {
-		if (mv88e6352_serdes_p2p_to_reg[i] == val) {
-			reg = i;
-			found = true;
-			break;
-		}
-	}
-
-	if (!found)
-		return -EINVAL;
-
-	err = mv88e6352_serdes_read(chip, MV88E6352_SERDES_SPEC_CTRL2, &ctrl);
-	if (err)
-		return err;
-
-	ctrl &= ~MV88E6352_SERDES_OUT_AMP_MASK;
-	ctrl |= reg;
-
-	return mv88e6352_serdes_write(chip, MV88E6352_SERDES_SPEC_CTRL2, ctrl);
 }

drivers/net/dsa/mv88e6xxx/serdes.h

···
 #define MV88E6352_SERDES_INT_FIBRE_ENERGY	BIT(4)
 #define MV88E6352_SERDES_INT_STATUS	0x13
 
-#define MV88E6352_SERDES_SPEC_CTRL2	0x1a
-#define MV88E6352_SERDES_OUT_AMP_MASK		0x0007
 
 #define MV88E6341_PORT5_LANE		0x15
 
···
 void mv88e6352_serdes_get_regs(struct mv88e6xxx_chip *chip, int port, void *_p);
 int mv88e6390_serdes_get_regs_len(struct mv88e6xxx_chip *chip, int port);
 void mv88e6390_serdes_get_regs(struct mv88e6xxx_chip *chip, int port, void *_p);
-
-int mv88e6352_serdes_set_tx_amplitude(struct mv88e6xxx_chip *chip, int port,
-				      int val);
 
 /* Return the (first) SERDES lane address a port is using, -errno otherwise. */
 static inline int mv88e6xxx_serdes_get_lane(struct mv88e6xxx_chip *chip,