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Date: Sat, 25 Nov 2023 17:50:10 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Andrew Halaney <ahalaney@...hat.com>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
Russell King <linux@...linux.org.uk>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
Sagar Cheluvegowda <quic_scheluve@...cinc.com>
Subject: Re: [PATCH net-next] net: phy: mdio_device: Reset device only when
necessary
On Tue, Nov 21, 2023 at 04:10:37PM -0600, Andrew Halaney wrote:
> 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.
>
> 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.
This only talks about GPIOs. There is also support for a linux reset
controller. It is getting turned on/off as many times. You should
mention this.
Now, lets compare the GPIO and the reset controller:
static int mdiobus_register_gpiod(struct mdio_device *mdiodev)
{
/* Deassert the optional reset signal */
mdiodev->reset_gpio = gpiod_get_optional(&mdiodev->dev,
"reset", GPIOD_OUT_LOW);
if (IS_ERR(mdiodev->reset_gpio))
return PTR_ERR(mdiodev->reset_gpio);
if (mdiodev->reset_gpio)
gpiod_set_consumer_name(mdiodev->reset_gpio, "PHY reset");
return 0;
}
static int mdiobus_register_reset(struct mdio_device *mdiodev)
{
struct reset_control *reset;
reset = reset_control_get_optional_exclusive(&mdiodev->dev, "phy");
if (IS_ERR(reset))
return PTR_ERR(reset);
mdiodev->reset_ctrl = reset;
return 0;
}
For the GPIO controller, its clear what state it is in, because the
get call sets it to GPIOD_OUT_LOW. The reset controller however does
not have a clear state, we just get a reference to it.
But:
in mdiobus_register_device() we have:
err = mdiobus_register_reset(mdiodev);
if (err)
return err;
/* Assert the reset signal */
mdio_device_reset(mdiodev, 1);
suggesting the reset controller might have the opposite state to the
GPIO?
> diff --git a/drivers/net/phy/mdio_device.c b/drivers/net/phy/mdio_device.c
> index 044828d081d2..d2b9e62edaaa 100644
> --- a/drivers/net/phy/mdio_device.c
> +++ b/drivers/net/phy/mdio_device.c
> @@ -122,6 +122,9 @@ void mdio_device_reset(struct mdio_device *mdiodev, int value)
> if (!mdiodev->reset_gpio && !mdiodev->reset_ctrl)
> return;
>
> + if (mdiodev->reset_state == value)
> + return;
> +
mdiodev is set to all 0 at creation time, and the GPIO is also set to
LOW when we get it. However, what about the reset controller?
I think it would be better to initialize reset_state to -1, indicating
we have no idea what the state is, and always perform the first reset
to ensure we are into a know state for both GPIO and the reset
controller.
Andrew
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