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

Russell King (Oracle)
2022-12-15T17:09:50Z

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 <ansuelsmth@gmail.com>
> ---
> 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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