linux-kernel - [PATCH] net: mdio: force deassert MDIO reset signal

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Message-Id: <20230115161006.16431-1-pierluigi.p@variscite.com>
Date:   Sun, 15 Jan 2023 17:10:06 +0100
From:   Pierluigi Passaro <pierluigi.passaro@...il.com>
To:     andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     eran.m@...iscite.com, nate.d@...iscite.com,
        francesco.f@...iscite.com, pierluigi.p@...iscite.com
Subject: [PATCH] net: mdio: force deassert MDIO reset signal

When the reset gpio is defined within the node of the device tree
describing the PHY, the reset is initialized and managed only after
calling the fwnode_mdiobus_phy_device_register function.
However, before calling it, the MDIO communication is checked by the
get_phy_device function.
When this happen and the reset GPIO was somehow previously set down,
the get_phy_device function fails, preventing the PHY detection.
These changes force the deassert of the MDIO reset signal before
checking the MDIO channel.
The PHY may require a minimum deassert time before being responsive:
use a reasonable sleep time after forcing the deassert of the MDIO
reset signal.
Once done, free the gpio descriptor to allow managing it later.

Signed-off-by: Pierluigi Passaro <pierluigi.p@...iscite.com>
Signed-off-by: FrancescoFerraro <francesco.f@...iscite.com>
---
 drivers/net/mdio/fwnode_mdio.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
index b782c35c4ac1..1f4b8c4c1f60 100644
--- a/drivers/net/mdio/fwnode_mdio.c
+++ b/drivers/net/mdio/fwnode_mdio.c
@@ -8,6 +8,8 @@
 
 #include <linux/acpi.h>
 #include <linux/fwnode_mdio.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
 #include <linux/of.h>
 #include <linux/phy.h>
 #include <linux/pse-pd/pse.h>
@@ -118,6 +120,8 @@ int fwnode_mdiobus_register_phy(struct mii_bus *bus,
 	bool is_c45 = false;
 	u32 phy_id;
 	int rc;
+	int reset_deassert_delay = 0;
+	struct gpio_desc *reset_gpio;
 
 	psec = fwnode_find_pse_control(child);
 	if (IS_ERR(psec))
@@ -134,10 +138,31 @@ int fwnode_mdiobus_register_phy(struct mii_bus *bus,
 	if (rc >= 0)
 		is_c45 = true;
 
+	reset_gpio = fwnode_gpiod_get_index(child, "reset", 0, GPIOD_OUT_LOW, "PHY reset");
+	if (reset_gpio == ERR_PTR(-EPROBE_DEFER)) {
+		dev_dbg(&bus->dev, "reset signal for PHY@%u not ready\n", addr);
+		return -EPROBE_DEFER;
+	} else if (IS_ERR(reset_gpio)) {
+		if (reset_gpio == ERR_PTR(-ENOENT))
+			dev_dbg(&bus->dev, "reset signal for PHY@%u not defined\n", addr);
+		else
+			dev_dbg(&bus->dev, "failed to request reset for PHY@%u, error %ld\n", addr, PTR_ERR(reset_gpio));
+		reset_gpio = NULL;
+	} else {
+		dev_dbg(&bus->dev, "deassert reset signal for PHY@%u\n", addr);
+		fwnode_property_read_u32(child, "reset-deassert-us",
+					 &reset_deassert_delay);
+		if (reset_deassert_delay)
+			fsleep(reset_deassert_delay);
+	}
+
 	if (is_c45 || fwnode_get_phy_id(child, &phy_id))
 		phy = get_phy_device(bus, addr, is_c45);
 	else
 		phy = phy_device_create(bus, addr, phy_id, 0, NULL);
+
+	gpiochip_free_own_desc(reset_gpio);
+
 	if (IS_ERR(phy)) {
 		rc = PTR_ERR(phy);
 		goto clean_mii_ts;
-- 
2.37.2