[PATCH net-next v2] net: phy: mdio_device: Reset device only when necessary

[Andrew Halaney <ahalaney@redhat.com>]

Currently the phy reset sequence is as shown below for a
devicetree described mdio phy on boot:

1. Assert the phy_device's reset as part of registering
2. Deassert the phy_device's reset as part of registering
3. Deassert the phy_device's reset as part of phy_probe
4. Deassert the phy_device's reset as part of phy_hw_init

The extra two deasserts include waiting the deassert delay afterwards,
which is adding unnecessary delay.

This applies to both possible types of resets (reset controller
reference and a reset gpio) that can be used.

Here's some snipped tracing output using the following command line
params "trace_event=gpio:* trace_options=stacktrace" illustrating
the reset handling and where its coming from:

    /* Assert */
       systemd-udevd-283     [002] .....     6.780434: gpio_value: 544 set 0
       systemd-udevd-283     [002] .....     6.783849: <stack trace>
     => gpiod_set_raw_value_commit
     => gpiod_set_value_nocheck
     => gpiod_set_value_cansleep
     => mdio_device_reset
     => mdiobus_register_device
     => phy_device_register
     => fwnode_mdiobus_phy_device_register
     => fwnode_mdiobus_register_phy
     => __of_mdiobus_register
     => stmmac_mdio_register
     => stmmac_dvr_probe
     => stmmac_pltfr_probe
     => devm_stmmac_pltfr_probe
     => qcom_ethqos_probe
     => platform_probe

    /* Deassert */
       systemd-udevd-283     [002] .....     6.802480: gpio_value: 544 set 1
       systemd-udevd-283     [002] .....     6.805886: <stack trace>
     => gpiod_set_raw_value_commit
     => gpiod_set_value_nocheck
     => gpiod_set_value_cansleep
     => mdio_device_reset
     => phy_device_register
     => fwnode_mdiobus_phy_device_register
     => fwnode_mdiobus_register_phy
     => __of_mdiobus_register
     => stmmac_mdio_register
     => stmmac_dvr_probe
     => stmmac_pltfr_probe
     => devm_stmmac_pltfr_probe
     => qcom_ethqos_probe
     => platform_probe

    /* Deassert */
       systemd-udevd-283     [002] .....     6.882601: gpio_value: 544 set 1
       systemd-udevd-283     [002] .....     6.886014: <stack trace>
     => gpiod_set_raw_value_commit
     => gpiod_set_value_nocheck
     => gpiod_set_value_cansleep
     => mdio_device_reset
     => phy_probe
     => really_probe
     => __driver_probe_device
     => driver_probe_device
     => __device_attach_driver
     => bus_for_each_drv
     => __device_attach
     => device_initial_probe
     => bus_probe_device
     => device_add
     => phy_device_register
     => fwnode_mdiobus_phy_device_register
     => fwnode_mdiobus_register_phy
     => __of_mdiobus_register
     => stmmac_mdio_register
     => stmmac_dvr_probe
     => stmmac_pltfr_probe
     => devm_stmmac_pltfr_probe
     => qcom_ethqos_probe
     => platform_probe

    /* Deassert */
      NetworkManager-477     [000] .....     7.023144: gpio_value: 544 set 1
      NetworkManager-477     [000] .....     7.026596: <stack trace>
     => gpiod_set_raw_value_commit
     => gpiod_set_value_nocheck
     => gpiod_set_value_cansleep
     => mdio_device_reset
     => phy_init_hw
     => phy_attach_direct
     => phylink_fwnode_phy_connect
     => __stmmac_open
     => stmmac_open

There's a lot of paths where the device is getting its reset
asserted and deasserted. Let's track the state and only actually
do the assert/deassert when it changes.

Reported-by: Sagar Cheluvegowda <quic_scheluve@quicinc.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
---
Changes in v2:
- Mention the reset controller in the commit message (Andrew Lunn)
- Make the initial reset_state unknown (so we always ensure the reset
  gpio and controller end up in the same state) instead of
  assuming they're both out of reset after acquiring them (Andrew Lunn)
- Link to v1: https://lore.kernel.org/r/20231121-net-phy-reset-once-v1-1-37c960b6336c@redhat.com
---
 drivers/net/phy/mdio_device.c | 6 ++++++
 drivers/net/phy/phy_device.c  | 1 +
 include/linux/mdio.h          | 1 +
 3 files changed, 8 insertions(+)

diff --git a/drivers/net/phy/mdio_device.c b/drivers/net/phy/mdio_device.c
index 044828d081d2..73f6539b9e50 100644
--- a/drivers/net/phy/mdio_device.c
+++ b/drivers/net/phy/mdio_device.c
@@ -62,6 +62,7 @@ struct mdio_device *mdio_device_create(struct mii_bus *bus, int addr)
 	mdiodev->device_remove = mdio_device_remove;
 	mdiodev->bus = bus;
 	mdiodev->addr = addr;
+	mdiodev->reset_state = -1;
 
 	dev_set_name(&mdiodev->dev, PHY_ID_FMT, bus->id, addr);
 
@@ -122,6 +123,9 @@ void mdio_device_reset(struct mdio_device *mdiodev, int value)
 	if (!mdiodev->reset_gpio && !mdiodev->reset_ctrl)
 		return;
 
+	if (mdiodev->reset_state == value)
+		return;
+
 	if (mdiodev->reset_gpio)
 		gpiod_set_value_cansleep(mdiodev->reset_gpio, value);
 
@@ -135,6 +139,8 @@ void mdio_device_reset(struct mdio_device *mdiodev, int value)
 	d = value ? mdiodev->reset_assert_delay : mdiodev->reset_deassert_delay;
 	if (d)
 		fsleep(d);
+
+	mdiodev->reset_state = value;
 }
 EXPORT_SYMBOL(mdio_device_reset);
 
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 478126f6b5bc..843ce2479736 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -654,6 +654,7 @@ struct phy_device *phy_device_create(struct mii_bus *bus, int addr, u32 phy_id,
 	mdiodev->flags = MDIO_DEVICE_FLAG_PHY;
 	mdiodev->device_free = phy_mdio_device_free;
 	mdiodev->device_remove = phy_mdio_device_remove;
+	mdiodev->reset_state = -1;
 
 	dev->speed = SPEED_UNKNOWN;
 	dev->duplex = DUPLEX_UNKNOWN;
diff --git a/include/linux/mdio.h b/include/linux/mdio.h
index 007fd9c3e4b6..79ceee3c8673 100644
--- a/include/linux/mdio.h
+++ b/include/linux/mdio.h
@@ -38,6 +38,7 @@ struct mdio_device {
 	/* Bus address of the MDIO device (0-31) */
 	int addr;
 	int flags;
+	int reset_state;
 	struct gpio_desc *reset_gpio;
 	struct reset_control *reset_ctrl;
 	unsigned int reset_assert_delay;

---
base-commit: 48bbaf8b793e0770798519f8ee1ea2908ff0943a
change-id: 20231121-net-phy-reset-once-1e2323982ae0

Best regards,
-- 
Andrew Halaney <ahalaney@redhat.com>