netdev - Re: [PATCH] leds: trigger: netdev: Check offload ability on interface up

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Message-ID: <1d72f370-3409-4b0f-b971-8f194cf1644b@lunn.ch>
Date: Thu, 3 Oct 2024 01:21:54 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Marek Vasut <marex@...x.de>
Cc: linux-leds@...r.kernel.org,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Christian Marangi <ansuelsmth@...il.com>,
	Christophe Roullier <christophe.roullier@...s.st.com>,
	Daniel Golle <daniel@...rotopia.org>,
	Heiner Kallweit <hkallweit1@...il.com>, Lee Jones <lee@...nel.org>,
	Lukasz Majewski <lukma@...x.de>, Pavel Machek <pavel@....cz>,
	kernel@...electronics.com, linux-stm32@...md-mailman.stormreply.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] leds: trigger: netdev: Check offload ability on
 interface up

On Tue, Oct 01, 2024 at 04:45:23AM +0200, Marek Vasut wrote:
> The trigger_data->hw_control indicates whether the LED is controlled by HW
> offload, i.e. the PHY. The trigger_data->hw_control = can_hw_control() is
> currently called only from netdev_led_attr_store(), i.e. when writing any
> sysfs attribute of the netdev trigger instance associated with a PHY LED.
> 
> The can_hw_control() calls validate_net_dev() which internally calls
> led_cdev->hw_control_get_device(), which is phy_led_hw_control_get_device()
> for PHY LEDs. The phy_led_hw_control_get_device() returns NULL if the PHY
> is not attached.
> 
> At least in case of DWMAC (STM32MP, iMX8M, ...), the PHY device is attached
> only when the interface is brought up and is detached again when the
> interface is brought down. In case e.g. udev rules configure the netdev
> LED trigger sysfs attributes before the interface is brought up, then when
> the interface is brought up, the LEDs are not blinking.
> 
> This is because trigger_data->hw_control = can_hw_control() was called
> when udev wrote the sysfs attribute files, before the interface was up,
> so can_hw_control() resp. validate_net_dev() returned false, and the
> trigger_data->hw_control = can_hw_control() was never called again to
> update the trigger_data->hw_control content and let the offload take
> over the LED blinking.
> 
> Call data->hw_control = can_hw_control() from netdev_trig_notify() to
> update the offload capability of the LED when the UP notification arrives.
> This makes the LEDs blink after the interface is brought up.

Have you run this code with lockdep enabled? There have been some
deadlocks, or potential deadlocks in this area.

> 
> On STM32MP13xx with RTL8211F, it is enough to have the following udev rule
> in place, boot the machine with cable plugged in, and the LEDs won't work
> without this patch once the interface is brought up, even if they should:
> "
> ACTION=="add", SUBSYSTEM=="leds", KERNEL=="stmmac-0:01:green:wan", ATTR{trigger}="netdev", ATTR{link_10}="1", ATTR{link_100}="1", ATTR{link_1000}="1", ATTR{device_name}="end0"
> ACTION=="add", SUBSYSTEM=="leds", KERNEL=="stmmac-0:01:yellow:wan", ATTR{trigger}="netdev", ATTR{rx}="1", ATTR{tx}="1", ATTR{device_name}="end0"
> "

Nice use of udev. I had not thought about using it for this.

	Andrew