Subject: [PATCH v3 1/3] leds: triggers: Allow to switch the trigger to "panic" on a kernel panic

From: [email-masked] (Jacek Anaszewski)
Date: Fri, 29 Apr 2016 09:20:06 +0200

Hi Ezequiel,

Thanks for the update. It's indeed reasonable to have all the
switching infrastructure in ledtrig-panic.c.

I've noticed two minor issues below.

On 04/29/2016 12:03 AM, Ezequiel Garcia wrote:
> This commit adds a new led_cdev flag LED_PANIC_INDICATOR, which
> allows to mark a specific LED to be switched to the "panic"
> trigger, on a kernel panic.
>
> This is useful to allow the user to assign a regular trigger
> to a given LED, and still blink that LED on a kernel panic.
>
> Signed-off-by: Ezequiel Garcia <[email-masked]>
> ---
>   drivers/leds/led-triggers.c          |  2 +-
>   drivers/leds/leds.h                  |  1 +
>   drivers/leds/trigger/Kconfig         |  3 +++
>   drivers/leds/trigger/ledtrig-panic.c | 47 ++++++++++++++++++++++++++++++++++++
>   include/linux/leds.h                 |  1 +
>   5 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> index 2181581795d3..55fa65e1ae03 100644
> --- a/drivers/leds/led-triggers.c
> +++ b/drivers/leds/led-triggers.c
> @@ -26,7 +26,7 @@
>    * Nests outside led_cdev->trigger_lock
>    */
>   static DECLARE_RWSEM(triggers_list_lock);
> -static LIST_HEAD(trigger_list);
> +LIST_HEAD(trigger_list);
>
>    /* Used by LED Class */
>
> diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
> index db3f20da7221..7d38e6b9a740 100644
> --- a/drivers/leds/leds.h
> +++ b/drivers/leds/leds.h
> @@ -30,5 +30,6 @@ void led_set_brightness_nosleep(struct led_classdev *led_cdev,
>
>   extern struct rw_semaphore leds_list_lock;
>   extern struct list_head leds_list;
> +extern struct list_head trigger_list;
>
>   #endif	/* __LEDS_H_INCLUDED */
> diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
> index beac8c31c51b..4e4521c9072a 100644
> --- a/drivers/leds/trigger/Kconfig
> +++ b/drivers/leds/trigger/Kconfig
> @@ -121,6 +121,9 @@ config LEDS_TRIGGER_PANIC
>   	depends on LEDS_TRIGGERS
>   	help
>   	  This allows LEDs to be configured to blink on a kernel panic.
> +	  Enabling this option will allow to mark certain LEDs as 'panic-indicators',

s/"panic-indicators"/panic indicators/

I understand that you referred here to the DT property name, but this
is not obvious at first glance, and it is an implementation detail.

> +	  allowing to blink them on a kernel panic, even if they are set to
> +	  a different trigger.
>   	  If unsure, say Y.
>
>   endif # LEDS_TRIGGERS
> diff --git a/drivers/leds/trigger/ b/drivers/leds/trigger/ledtrig-panic.c
> index 627b350c5ec3..3e447bd2064a 100644
> --- a/drivers/leds/trigger/ledtrig-panic.c
> +++ b/drivers/leds/trigger/ledtrig-panic.c
> @@ -11,10 +11,54 @@
>
>   #include <linux/kernel.h>
>   #include <linux/init.h>
> +#include <linux/notifier.h>
>   #include <linux/leds.h>
> +#include "../leds.h"
>
>   static struct led_trigger *trigger;
>
> +/*
> + * This is a called in a special context by the atomic panic

s/is a/is/

> + * notifier. This means the trigger can be changed without
> + * worrying about locking.
> + */
> +static void led_trigger_set_panic(struct led_classdev *led_cdev)
> +{
> +	struct led_trigger *trig;
> +
> +	list_for_each_entry(trig, &trigger_list, next_trig) {
> +		if (strcmp("panic", trig->name))
> +			continue;
> +		if (led_cdev->trigger)
> +			list_del(&led_cdev->trig_list);
> +		list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
> +
> +		/* Avoid the delayed blink path */
> +		led_cdev->blink_delay_on = 0;
> +		led_cdev->blink_delay_off = 0;
> +
> +		led_cdev->trigger = trig;
> +		if (trig->activate)
> +			trig->activate(led_cdev);
> +		break;
> +	}
> +}
> +
> +static int led_trigger_panic_notifier(struct notifier_block *nb,
> +				      unsigned long code, void *unused)
> +{
> +	struct led_classdev *led_cdev;
> +
> +	list_for_each_entry(led_cdev, &leds_list, node)
> +		if (led_cdev->flags & LED_PANIC_INDICATOR)
> +			led_trigger_set_panic(led_cdev);
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block led_trigger_panic_nb = {
> +	.notifier_call = led_trigger_panic_notifier,
> +};
> +
>   static long led_panic_blink(int state)
>   {
>   	led_trigger_event(trigger, state ? LED_FULL : LED_OFF);
> @@ -23,6 +67,9 @@ static long led_panic_blink(int state)
>
>   static int __init ledtrig_panic_init(void)
>   {
> +	atomic_notifier_chain_register(&panic_notifier_list,
> +				       &led_trigger_panic_nb);
> +
>   	led_trigger_register_simple("panic", &trigger);
>   	panic_blink = led_panic_blink;
>   	return 0;
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index 19eb10278bea..7e9fb00e15e8 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -50,6 +50,7 @@ struct led_classdev {
>   #define LED_SYSFS_DISABLE	(1 << 22)
>   #define LED_DEV_CAP_FLASH	(1 << 23)
>   #define LED_HW_PLUGGABLE	(1 << 24)
> +#define LED_PANIC_INDICATOR	(1 << 25)
>
>   	/* Set LED brightness level
>   	 * Must not sleep. Use brightness_set_blocking for drivers
>

-- 
Best regards,
Jacek Anaszewski