[PATCH net-next v11 07/10] net: mdio: realtek-rtl9300: Add page tracking

[Markus Stockhausen <markus.stockhausen@gmx.de>]

The hardware polling unit of the Realtek switches has a very special
handling for c22 PHY register 31 (aka Realtek page register) in place.

- On the RTL838x it is permanently reset to zero.
- On other devices there is some magic saving/restoring (aka parking)
  in the background in place.

This makes access to PHYs a gamble.

It is vital to keep the polling alive so the MAC layer can rely on
consistent data. Intercept access to c22 register 31 and handle it
internally. Store the desired value for each port in the driver. When
issuing hardware access to other registers add the page to the command
towards the controller. Given this, the hardware will run two c22
commands that are not interrupted by polling.

  ... hardware poll ...
  phy_write(phy, 31, page)
  phy_write(phy, reg, value)
  ... hardware poll ...

Looking at this implementation one might argue that disabling/enabling
polling might be a cleaner solution. But one must remember that

- This driver differentiates clearly between C22 and C45 buses. During
  probing it enables only one of the protocols for a bus.
- All known devices run RTL8218 (B/D/E) or RTL8214FC on 1G
- RTL839x gives link flapping when deactivating polling for a port

So a solution for a Realtek-only ecosystem is required. This commit
copies the downstream-proven driver-only page handling patch without
any new MDIO callbacks and is the lowest common denominator. If a
non-Realtek PHY is identified on a c22 bus the attachment aborts. It
should be noted that bus scan runs with the page handling already in
place before the check in notify_phy_attach(). This is accepted for
now.

Remark: To keep this simple, writes to register 31 are only accepted
if they are lower than the device specific raw page - 0..4094/8190.
Otherwise -EINVAL is returned. Under the above assumption (Only 1G
Realtek PHYs on a c22 bus) this is no limitation.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
---
 drivers/net/mdio/mdio-realtek-rtl9300.c | 46 +++++++++++++++++++++----
 1 file changed, 39 insertions(+), 7 deletions(-)

diff --git a/drivers/net/mdio/mdio-realtek-rtl9300.c b/drivers/net/mdio/mdio-realtek-rtl9300.c
index 161df1818d02..95641052bc9b 100644
--- a/drivers/net/mdio/mdio-realtek-rtl9300.c
+++ b/drivers/net/mdio/mdio-realtek-rtl9300.c
@@ -178,6 +178,9 @@
 #define PHY_CTRL_MMD_DEVAD			GENMASK(20, 16)
 #define PHY_CTRL_MMD_REG			GENMASK(15, 0)
 
+#define RTL_VENDOR_ID				0x001cc800
+#define RTL_PAGE_SELECT				31
+
 #define MAP_ADDRS_PER_REG			6
 #define MAP_BITS_PER_ADDR			5
 #define MAP_BITS_PER_BUS			2
@@ -203,6 +206,7 @@ struct otto_emdio_priv {
 	struct regmap *regmap;
 	struct mutex lock; /* protect HW access */
 	DECLARE_BITMAP(valid_ports, MAX_PORTS);
+	u16 page[MAX_PORTS];
 	u8 smi_bus[MAX_PORTS];
 	u8 smi_addr[MAX_PORTS];
 	bool smi_bus_is_c45[MAX_SMI_BUSSES];
@@ -354,7 +358,7 @@ static int otto_emdio_9300_read_c22(struct mii_bus *bus, int port, int regnum, u
 	struct otto_emdio_cmd_regs cmd_data = {
 		.c22_data	= FIELD_PREP(RTL9300_PHY_CTRL_REG_ADDR, regnum) |
 				  FIELD_PREP(RTL9300_PHY_CTRL_PARK_PAGE, 0x1f) |
-				  FIELD_PREP(RTL9300_PHY_CTRL_MAIN_PAGE, RAW_PAGE(priv)),
+				  FIELD_PREP(RTL9300_PHY_CTRL_MAIN_PAGE, priv->page[port]),
 		.io_data	= FIELD_PREP(RTL9300_PHY_CTRL_INDATA, port),
 	};
 
@@ -368,7 +372,7 @@ static int otto_emdio_9300_write_c22(struct mii_bus *bus, int port, int regnum,
 	struct otto_emdio_cmd_regs cmd_data = {
 		.c22_data	= FIELD_PREP(RTL9300_PHY_CTRL_REG_ADDR, regnum) |
 				  FIELD_PREP(RTL9300_PHY_CTRL_PARK_PAGE, 0x1f) |
-				  FIELD_PREP(RTL9300_PHY_CTRL_MAIN_PAGE, RAW_PAGE(priv)),
+				  FIELD_PREP(RTL9300_PHY_CTRL_MAIN_PAGE, priv->page[port]),
 		.io_data	= FIELD_PREP(RTL9300_PHY_CTRL_INDATA, value),
 		.port_mask_low	= BIT(port),
 	};
@@ -408,7 +412,7 @@ static int otto_emdio_9310_read_c22(struct mii_bus *bus, int port, int regnum, u
 	struct otto_emdio_cmd_regs cmd_data = {
 		.broadcast	= FIELD_PREP(RTL9310_BC_PORT_ID, port),
 		.c22_data	= FIELD_PREP(RTL9310_PHY_CTRL_REG_ADDR, regnum) |
-				  FIELD_PREP(RTL9310_PHY_CTRL_MAIN_PAGE, RAW_PAGE(priv)),
+				  FIELD_PREP(RTL9310_PHY_CTRL_MAIN_PAGE, priv->page[port]),
 	};
 
 	return otto_emdio_read_cmd(bus, RTL9310_PHY_CTRL_TYPE_C22, &cmd_data,
@@ -420,7 +424,7 @@ static int otto_emdio_9310_write_c22(struct mii_bus *bus, int port, int regnum,
 	struct otto_emdio_priv *priv = otto_emdio_bus_to_priv(bus);
 	struct otto_emdio_cmd_regs cmd_data = {
 		.c22_data	= FIELD_PREP(RTL9310_PHY_CTRL_REG_ADDR, regnum) |
-				  FIELD_PREP(RTL9310_PHY_CTRL_MAIN_PAGE, RAW_PAGE(priv)),
+				  FIELD_PREP(RTL9310_PHY_CTRL_MAIN_PAGE, priv->page[port]),
 		.io_data	= FIELD_PREP(RTL9310_PHY_CTRL_INDATA, value),
 		.port_mask_high	= (u32)(BIT_ULL(port) >> 32),
 		.port_mask_low	= (u32)(BIT_ULL(port)),
@@ -466,8 +470,12 @@ static int otto_emdio_read_c22(struct mii_bus *bus, int phy_id, int regnum)
 	if (port < 0)
 		return port;
 
-	scoped_guard(mutex, &priv->lock)
+	scoped_guard(mutex, &priv->lock) {
+		if (regnum == RTL_PAGE_SELECT)
+			return priv->page[port];
+
 		ret = priv->info->read_c22(bus, port, regnum, &value);
+	}
 
 	return ret ? ret : value;
 }
@@ -481,8 +489,17 @@ static int otto_emdio_write_c22(struct mii_bus *bus, int phy_id, int regnum, u16
 	if (port < 0)
 		return port;
 
-	scoped_guard(mutex, &priv->lock)
+	scoped_guard(mutex, &priv->lock) {
+		if (regnum == RTL_PAGE_SELECT) {
+			if (value >= RAW_PAGE(priv))
+				return -EINVAL;
+
+			priv->page[port] = value;
+			return 0;
+		}
+
 		ret = priv->info->write_c22(bus, port, regnum, value);
+	}
 
 	return ret;
 }
@@ -593,12 +610,23 @@ static int otto_emdio_9310_setup_controller(struct otto_emdio_priv *priv)
 
 static int otto_emdio_notify_phy_attach(struct phy_device *phydev)
 {
-	struct otto_emdio_priv *priv = otto_emdio_bus_to_priv(phydev->mdio.bus);
 	int port = otto_emdio_phy_to_port(phydev->mdio.bus, phydev->mdio.addr);
+	struct otto_emdio_chan *chan = phydev->mdio.bus->priv;
+	struct otto_emdio_priv *priv = chan->priv;
 
 	if (port < 0)
 		return port;
 
+	/* "sync" page in case of previously failed attachment */
+	scoped_guard(mutex, &priv->lock)
+		priv->page[port] = 0;
+
+	if (!priv->smi_bus_is_c45[chan->mdio_bus] &&
+	    !phy_id_compare_vendor(phydev->phy_id, RTL_VENDOR_ID)) {
+		phydev_err(phydev, "Only Realtek PHYs allowed on C22 bus\n");
+		return -EOPNOTSUPP;
+	}
+
 	return otto_emdio_set_port_polling(priv, port, true);
 }
 
@@ -618,6 +646,10 @@ static void otto_emdio_notify_phy_detach(struct phy_device *phydev)
 	if (port < 0)
 		return;
 
+	/* "sync" page for next attachment */
+	scoped_guard(mutex, &priv->lock)
+		priv->page[port] = 0;
+
 	if (otto_emdio_set_port_polling(priv, port, false))
 		dev_err(bus->parent, "failed to disable polling for port %d\n", port);
 }
-- 
2.55.0