[PATCH v1 1/3] net: port support for microchip SMI0 MDIO bus

[Oleksij Rempel]

SMI0 is a mangled version of MDIO. The main low level difference is
the MDIO C22 OP code is always 0, not 0x2 or 0x1 for Read/Write. The
read/write information is instead encoded in the PHY address.

Extend the bit-bang code to allow the op code to be overridden, but
default to normal C22 values. Add an extra compatible to the mdio-gpio
driver, and when this compatible is present, set the op codes to 0.

A higher level driver, sitting on top of the basic MDIO bus driver can
then implement the rest of the microchip SMI0 odderties.

This code was ported from the kernel v6.0-rc2.

Signed-off-by: Oleksij Rempel <o.rempel at pengutronix.de>
---
 drivers/net/phy/mdio-bitbang.c | 8 ++++++--
 drivers/net/phy/mdio-gpio.c    | 8 ++++++++
 include/linux/mdio-bitbang.h   | 3 +++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/mdio-bitbang.c b/drivers/net/phy/mdio-bitbang.c
index 839a7d1eb8..656557589d 100644
--- a/drivers/net/phy/mdio-bitbang.c
+++ b/drivers/net/phy/mdio-bitbang.c
@@ -158,7 +158,7 @@ static int mdiobb_read(struct mii_bus *bus, int phy, int reg)
 		reg = mdiobb_cmd_addr(ctrl, phy, reg);
 		mdiobb_cmd(ctrl, MDIO_C45_READ, phy, reg);
 	} else
-		mdiobb_cmd(ctrl, MDIO_READ, phy, reg);
+		mdiobb_cmd(ctrl, ctrl->op_c22_read, phy, reg);
 
 	ctrl->ops->set_mdio_dir(ctrl, 0);
 
@@ -188,7 +188,7 @@ static int mdiobb_write(struct mii_bus *bus, int phy, int reg, u16 val)
 		reg = mdiobb_cmd_addr(ctrl, phy, reg);
 		mdiobb_cmd(ctrl, MDIO_C45_WRITE, phy, reg);
 	} else
-		mdiobb_cmd(ctrl, MDIO_WRITE, phy, reg);
+		mdiobb_cmd(ctrl, ctrl->op_c22_write, phy, reg);
 
 	/* send the turnaround (10) */
 	mdiobb_send_bit(ctrl, 1);
@@ -219,6 +219,10 @@ struct mii_bus *alloc_mdio_bitbang(struct mdiobb_ctrl *ctrl)
 	bus->write = mdiobb_write;
 	bus->reset = mdiobb_reset;
 	bus->priv = ctrl;
+	if (!ctrl->override_op_c22) {
+		ctrl->op_c22_read = MDIO_READ;
+		ctrl->op_c22_write = MDIO_WRITE;
+	}
 
 	return bus;
 }
diff --git a/drivers/net/phy/mdio-gpio.c b/drivers/net/phy/mdio-gpio.c
index 80d2394f4b..c64f2b3925 100644
--- a/drivers/net/phy/mdio-gpio.c
+++ b/drivers/net/phy/mdio-gpio.c
@@ -193,6 +193,13 @@ static int mdio_gpio_probe(struct device_d *dev)
 		goto free_mdo;
 	}
 
+	if (np &&
+	    of_device_is_compatible(np, "microchip,mdio-smi0")) {
+		info->ctrl.op_c22_read = 0;
+		info->ctrl.op_c22_write = 0;
+		info->ctrl.override_op_c22 = 1;
+	}
+
 	bus = alloc_mdio_bitbang(&info->ctrl);
 	bus->parent = dev;
 	bus->dev.device_node = np;
@@ -217,6 +224,7 @@ free_info:
 
 static const struct of_device_id gpio_mdio_dt_ids[] = {
 	{ .compatible = "virtual,mdio-gpio", },
+	{ .compatible = "microchip,mdio-smi0" },
 	{ /* sentinel */ }
 };
 
diff --git a/include/linux/mdio-bitbang.h b/include/linux/mdio-bitbang.h
index a6e6057886..49fe435429 100644
--- a/include/linux/mdio-bitbang.h
+++ b/include/linux/mdio-bitbang.h
@@ -36,6 +36,9 @@ struct mdiobb_ctrl {
 	const struct mdiobb_ops *ops;
 	/* reset callback */
 	int (*reset)(struct mii_bus *bus);
+	unsigned int override_op_c22;
+	u8 op_c22_read;
+	u8 op_c22_write;
 };
 
 /* The returned bus is not yet registered with the phy layer. */
-- 
2.30.2