Subject: Re: [PATCH v7 06/11] leds: trigger: netdev: add hardware control support

From: "Russell King (Oracle)" <[email-masked]>
Date: Thu, 15 Dec 2022 17:07:31 +0000

On Thu, Dec 15, 2022 at 12:54:33AM +0100, Christian Marangi wrote:
> Add hardware control support for the Netdev trigger.
> The trigger on config change will check if the requested trigger can set
> to blink mode using LED hardware mode and if every blink mode is supported,
> the trigger will enable hardware mode with the requested configuration.
> If there is at least one trigger that is not supported and can't run in
> hardware mode, then software mode will be used instead.
> A validation is done on every value change and on fail the old value is
> restored and -EINVAL is returned.
> 
> Signed-off-by: Christian Marangi <[email-masked]>
> ---
>  drivers/leds/trigger/ledtrig-netdev.c | 155 +++++++++++++++++++++++++-
>  1 file changed, 149 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
> index dd63cadb896e..ed019cb5867c 100644
> --- a/drivers/leds/trigger/ledtrig-netdev.c
> +++ b/drivers/leds/trigger/ledtrig-netdev.c
> @@ -37,6 +37,7 @@
>   */
>  
>  struct led_netdev_data {
> +	enum led_blink_modes blink_mode;
>  	spinlock_t lock;
>  
>  	struct delayed_work work;
> @@ -53,11 +54,105 @@ struct led_netdev_data {
>  	bool carrier_link_up;
>  };
>  
> +struct netdev_led_attr_detail {
> +	char *name;
> +	bool hardware_only;
> +	enum led_trigger_netdev_modes bit;
> +};
> +
> +static struct netdev_led_attr_detail attr_details[] = {
> +	{ .name = "link", .bit = TRIGGER_NETDEV_LINK},
> +	{ .name = "tx", .bit = TRIGGER_NETDEV_TX},
> +	{ .name = "rx", .bit = TRIGGER_NETDEV_RX},
> +};
> +
> +static bool validate_baseline_state(struct led_netdev_data *trigger_data)
> +{
> +	struct led_classdev *led_cdev = trigger_data->led_cdev;
> +	struct netdev_led_attr_detail *detail;
> +	u32 hw_blink_mode_supported = 0;
> +	bool force_sw = false;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(attr_details); i++) {
> +		detail = &attr_details[i];
> +
> +		/* Mode not active, skip */
> +		if (!test_bit(detail->bit, &trigger_data->mode))
> +			continue;
> +
> +		/* Hardware only mode enabled on software controlled led */
> +		if (led_cdev->blink_mode == SOFTWARE_CONTROLLED &&
> +		    detail->hardware_only)
> +			return false;
> +
> +		/* Check if the mode supports hardware mode */
> +		if (led_cdev->blink_mode != SOFTWARE_CONTROLLED) {
> +			/* With a net dev set, force software mode.
> +			 * With modes are handled by hardware, led will blink
> +			 * based on his own events and will ignore any event
> +			 * from the provided dev.
> +			 */
> +			if (trigger_data->net_dev) {
> +				force_sw = true;
> +				continue;
> +			}
> +
> +			/* With empty dev, check if the mode is supported */
> +			if (led_trigger_blink_mode_is_supported(led_cdev, detail->bit))
> +				hw_blink_mode_supported |= BIT(detail->bit);
> +		}
> +	}
> +
> +	/* We can't run modes handled by both software and hardware.
> +	 * Check if we run hardware modes and check if all the modes
> +	 * can be handled by hardware.
> +	 */
> +	if (hw_blink_mode_supported && hw_blink_mode_supported != trigger_data->mode)
> +		return false;
> +
> +	/* Modes are valid. Decide now the running mode to later
> +	 * set the baseline.
> +	 * Software mode is enforced with net_dev set. With an empty
> +	 * one hardware mode is selected by default (if supported).
> +	 */
> +	if (force_sw || led_cdev->blink_mode == SOFTWARE_CONTROLLED)
> +		trigger_data->blink_mode = SOFTWARE_CONTROLLED;
> +	else
> +		trigger_data->blink_mode = HARDWARE_CONTROLLED;
> +
> +	return true;
> +}
> +
>  static void set_baseline_state(struct led_netdev_data *trigger_data)
>  {
> +	int i;
>  	int current_brightness;
> +	struct netdev_led_attr_detail *detail;
>  	struct led_classdev *led_cdev = trigger_data->led_cdev;
>  
> +	/* Modes already validated. Directly apply hw trigger modes */
> +	if (trigger_data->blink_mode == HARDWARE_CONTROLLED) {
> +		/* We are refreshing the blink modes. Reset them */
> +		led_cdev->hw_control_configure(led_cdev, BIT(TRIGGER_NETDEV_LINK),
> +					       BLINK_MODE_ZERO);
> +
> +		for (i = 0; i < ARRAY_SIZE(attr_details); i++) {
> +			detail = &attr_details[i];
> +
> +			if (!test_bit(detail->bit, &trigger_data->mode))
> +				continue;
> +
> +			led_cdev->hw_control_configure(led_cdev, BIT(detail->bit),
> +						       BLINK_MODE_ENABLE);
> +		}
> +
> +		led_cdev->hw_control_start(led_cdev);
> +
> +		return;
> +	}
> +
> +	/* Handle trigger modes by software */
>  	current_brightness = led_cdev->brightness;
>  	if (current_brightness)
>  		led_cdev->blink_brightness = current_brightness;
> @@ -100,10 +195,15 @@ static ssize_t device_name_store(struct device *dev,
>  				 size_t size)
>  {
>  	struct led_netdev_data *trigger_data = led_trigger_get_drvdata(dev);
> +	struct net_device *old_net = trigger_data->net_dev;
> +	char old_device_name[IFNAMSIZ];
>  
>  	if (size >= IFNAMSIZ)
>  		return -EINVAL;
>  
> +	/* Backup old device name */
> +	memcpy(old_device_name, trigger_data->device_name, IFNAMSIZ);
> +
>  	cancel_delayed_work_sync(&trigger_data->work);
>  
>  	spin_lock_bh(&trigger_data->lock);
> @@ -122,6 +222,19 @@ static ssize_t device_name_store(struct device *dev,
>  		trigger_data->net_dev =
>  		    dev_get_by_name(&init_net, trigger_data->device_name);
>  
> +	if (!validate_baseline_state(trigger_data)) {
> +		/* Restore old net_dev and device_name */
> +		if (trigger_data->net_dev)
> +			dev_put(trigger_data->net_dev);
> +
> +		dev_hold(old_net);
> +		trigger_data->net_dev = old_net;
> +		memcpy(trigger_data->device_name, old_device_name, IFNAMSIZ);
> +
> +		spin_unlock_bh(&trigger_data->lock);
> +		return -EINVAL;

I'm not sure this is the best way... putting the net_dev but holding a
reference, to leter regain the reference via dev_hold() just feels
wrong. Also, I wonder what happens if two threads try to change the
netdev together - will the read of the old device name be potentially
corrupted (since we're not holding the trigger's lock?)

Maybe instead:

+	struct net_device *old_net;
...
-	if (trigger_data->net_dev) {
-		dev_put(trigger_data->net_dev);
-		trigger_data->net_dev = NULL;
-	}
+	old_net = trigger_data->net_dev;
+	trigger_data->net_dev = NULL;
+	memcpy(old_device_name, trigger_data->device_name, IFNAMSIZ);
...
	... extract out the setup of trigger_data->device_name
...
+	if (!validate_baseline_state(trigger_data)) {
+		if (trigger_data->net_dev)
+			dev_put(trigger_data->net_dev);
+
+		/* Restore device settings */
+		trigger_data->net_dev = old_dev;
+		memcpy(trigger_data->device_name, old_device_name, IFNAMSIZ);
+		spin_unlock_bh(&trigger_data->lock);
+		return -EINVAL;
+	} else {
+		dev_put(old_net);
+	}

would be safer all round?

One thought on this approach though - if one has a PHY that supports
"activity" but not independent "rx" and "tx" activity indications
and it doesn't support software control, how would one enable activity
mode? There isn't a way to simultaneously enable both at the same
time... However, I need to check whether there are any PHYs that fall
into this category.

-- 
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