[PATCH v3 0/3] Extend the LED panic trigger

[PATCH v3 0/3] Extend the LED panic trigger

[Ezequiel Garcia]

As per commit 916fe619951f ("leds: trigger: Introduce a kernel
panic LED trigger"), the kernel now supports a new LED trigger
to hook on the panic blink.

However, the only way of using this is to dedicate a LED device,
making it rather useless.

To overcome this limitation, the present series introduces the
capability to switch the LED trigger of certain LED devices upon
a kernel panic (using the panic notifier).

The decision of which LEDs should be switched to the panic trigger
is left to each LED device driver. As an example, a devicetree
boolean property is introduced and used in the leds-gpio driver.

The big change in this v3 is that I've moved the panic trigger
switching away from the core code and it's now part of
ledtrig-panic.c. Pavel, Jacek: How does it look?

Changes from v2:

  * Added Rob's "panic-indicator" devicetree property Acked-by.

  * Fix typo, as pointed out by Robin Murphy.

  * Documented "panic-indicator" in bindings/leds/leds-gpio.txt.

  * Moved the panic trigger switching from the trigger core code,
    to ledtrig-panic.c.

Changes from v1:

  * Dropped the led_trigger_event_nosleep API, and instead just
    clear the blink_delay_{on, off} when the panic is notified. 
    This results in less changes.

  * Changed the flag to LED_PANIC_INDICATOR, as requested by Jacek.

  * Changed the firmware property name to "panic-indicator", as
    requested by Jacek. 

Ezequiel Garcia (3):
  leds: triggers: Allow to switch the trigger to "panic" on a kernel
    panic
  devicetree: leds: Introduce "panic-indicator" optional property
  leds: gpio: Support the "panic-indicator" firmware property

 Documentation/devicetree/bindings/leds/common.txt  |  3 ++
 .../devicetree/bindings/leds/leds-gpio.txt         |  2 +
 drivers/leds/led-triggers.c                        |  2 +-
 drivers/leds/leds-gpio.c                           |  4 ++
 drivers/leds/leds.h                                |  1 +
 drivers/leds/trigger/Kconfig                       |  3 ++
 drivers/leds/trigger/ledtrig-panic.c               | 47 ++++++++++++++++++++++
 include/linux/leds.h                               |  2 +
 8 files changed, 63 insertions(+), 1 deletion(-)

-- 
2.7.0

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

[Ezequiel Garcia]

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 <ezequiel@vanguardiasur.com.ar>
---
 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',
+	  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/ledtrig-panic.c 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
+ * 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
-- 
2.7.0

[PATCH v3 2/3] devicetree: leds: Introduce "panic-indicator" optional property

[Ezequiel Garcia]

It's desirable to specify which LEDs are to be blinked on a kernel
panic. Therefore, introduce a devicetree boolean property to mark
which LEDs should be treated this way, if possible.

Acked-by: Rob Herring <rob@kernel.org>
Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
---
 Documentation/devicetree/bindings/leds/common.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/common.txt b/Documentation/devicetree/bindings/leds/common.txt
index 68419843e32f..af10678ea2f6 100644
--- a/Documentation/devicetree/bindings/leds/common.txt
+++ b/Documentation/devicetree/bindings/leds/common.txt
@@ -37,6 +37,9 @@ Optional properties for child nodes:
                      property is mandatory for the LEDs in the non-flash modes
                      (e.g. torch or indicator).
 
+- panic-indicator : This property specifies that the LED should be used,
+		    if at all possible, as a panic indicator.
+
 Required properties for flash LED child nodes:
 - flash-max-microamp : Maximum flash LED supply current in microamperes.
 - flash-max-timeout-us : Maximum timeout in microseconds after which the flash
-- 
2.7.0

[PATCH v3 3/3] leds: gpio: Support the "panic-indicator" firmware property

[Ezequiel Garcia]

Calling a GPIO LEDs is quite likely to work even if the kernel
has paniced, so they are ideal to blink in this situation.
This commit adds support for the new "panic-indicator"
firmware property, allowing to mark a given LED to blink on
a kernel panic.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
---
 Documentation/devicetree/bindings/leds/leds-gpio.txt | 2 ++
 drivers/leds/leds-gpio.c                             | 4 ++++
 include/linux/leds.h                                 | 1 +
 3 files changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/leds-gpio.txt b/Documentation/devicetree/bindings/leds/leds-gpio.txt
index fea1ebfe24a9..cbbeb1850910 100644
--- a/Documentation/devicetree/bindings/leds/leds-gpio.txt
+++ b/Documentation/devicetree/bindings/leds/leds-gpio.txt
@@ -23,6 +23,8 @@ LED sub-node properties:
   property is not present.
 - retain-state-suspended: (optional) The suspend state can be retained.Such
   as charge-led gpio.
+- panic-indicator : (optional)
+  see Documentation/devicetree/bindings/leds/common.txt
 
 Examples:
 
diff --git a/drivers/leds/leds-gpio.c b/drivers/leds/leds-gpio.c
index 61143f55597e..8229f063b483 100644
--- a/drivers/leds/leds-gpio.c
+++ b/drivers/leds/leds-gpio.c
@@ -127,6 +127,8 @@ static int create_gpio_led(const struct gpio_led *template,
 	led_dat->cdev.brightness = state ? LED_FULL : LED_OFF;
 	if (!template->retain_state_suspended)
 		led_dat->cdev.flags |= LED_CORE_SUSPENDRESUME;
+	if (template->panic_indicator)
+		led_dat->cdev.flags |= LED_PANIC_INDICATOR;
 
 	ret = gpiod_direction_output(led_dat->gpiod, state);
 	if (ret < 0)
@@ -200,6 +202,8 @@ static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
 
 		if (fwnode_property_present(child, "retain-state-suspended"))
 			led.retain_state_suspended = 1;
+		if (fwnode_property_present(child, "panic-indicator"))
+			led.panic_indicator = 1;
 
 		ret = create_gpio_led(&led, &priv->leds[priv->num_leds],
 				      dev, NULL);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 7e9fb00e15e8..d2b13066e781 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -365,6 +365,7 @@ struct gpio_led {
 	unsigned 	gpio;
 	unsigned	active_low : 1;
 	unsigned	retain_state_suspended : 1;
+	unsigned	panic_indicator : 1;
 	unsigned	default_state : 2;
 	/* default_state should be one of LEDS_GPIO_DEFSTATE_(ON|OFF|KEEP) */
 	struct gpio_desc *gpiod;
-- 
2.7.0

Re: [PATCH v3 0/3] Extend the LED panic trigger

[Pavel Machek]

On Thu 2016-04-28 19:03:37, Ezequiel Garcia wrote:
> As per commit 916fe619951f ("leds: trigger: Introduce a kernel
> panic LED trigger"), the kernel now supports a new LED trigger
> to hook on the panic blink.
> 
> However, the only way of using this is to dedicate a LED device,
> making it rather useless.
> 
> To overcome this limitation, the present series introduces the
> capability to switch the LED trigger of certain LED devices upon
> a kernel panic (using the panic notifier).
> 
> The decision of which LEDs should be switched to the panic trigger
> is left to each LED device driver. As an example, a devicetree
> boolean property is introduced and used in the leds-gpio driver.
> 
> The big change in this v3 is that I've moved the panic trigger
> switching away from the core code and it's now part of
> ledtrig-panic.c. Pavel, Jacek: How does it look?

Seems better now. Thanks for doing that.

For the series:

Acked-by: Pavel Machek <pavel@ucw.cz>
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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

[Jacek Anaszewski]

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 <ezequiel@vanguardiasur.com.ar>
> ---
>   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

Re: [PATCH v3 0/3] Extend the LED panic trigger

[Matthias Brugger]

On 29/04/16 00:03, Ezequiel Garcia wrote:
> As per commit 916fe619951f ("leds: trigger: Introduce a kernel
> panic LED trigger"), the kernel now supports a new LED trigger
> to hook on the panic blink.
>
> However, the only way of using this is to dedicate a LED device,
> making it rather useless.
>
> To overcome this limitation, the present series introduces the
> capability to switch the LED trigger of certain LED devices upon
> a kernel panic (using the panic notifier).
>
> The decision of which LEDs should be switched to the panic trigger
> is left to each LED device driver. As an example, a devicetree
> boolean property is introduced and used in the leds-gpio driver.
>
> The big change in this v3 is that I've moved the panic trigger
> switching away from the core code and it's now part of
> ledtrig-panic.c. Pavel, Jacek: How does it look?
>
> Changes from v2:
>
>    * Added Rob's "panic-indicator" devicetree property Acked-by.
>
>    * Fix typo, as pointed out by Robin Murphy.
>
>    * Documented "panic-indicator" in bindings/leds/leds-gpio.txt.
>
>    * Moved the panic trigger switching from the trigger core code,
>      to ledtrig-panic.c.
>
> Changes from v1:
>
>    * Dropped the led_trigger_event_nosleep API, and instead just
>      clear the blink_delay_{on, off} when the panic is notified.
>      This results in less changes.
>
>    * Changed the flag to LED_PANIC_INDICATOR, as requested by Jacek.
>
>    * Changed the firmware property name to "panic-indicator", as
>      requested by Jacek.
>
> Ezequiel Garcia (3):
>    leds: triggers: Allow to switch the trigger to "panic" on a kernel
>      panic
>    devicetree: leds: Introduce "panic-indicator" optional property
>    leds: gpio: Support the "panic-indicator" firmware property
>
>   Documentation/devicetree/bindings/leds/common.txt  |  3 ++
>   .../devicetree/bindings/leds/leds-gpio.txt         |  2 +
>   drivers/leds/led-triggers.c                        |  2 +-
>   drivers/leds/leds-gpio.c                           |  4 ++
>   drivers/leds/leds.h                                |  1 +
>   drivers/leds/trigger/Kconfig                       |  3 ++
>   drivers/leds/trigger/ledtrig-panic.c               | 47 ++++++++++++++++++++++
>   include/linux/leds.h                               |  2 +
>   8 files changed, 63 insertions(+), 1 deletion(-)
>

Looks good to me.

Reviewed-by: Matthias Brugger <mbrugger-IBi9RG/b67k@public.gmane.org>
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Re: [PATCH v3 3/3] leds: gpio: Support the "panic-indicator" firmware property

[Rob Herring]

On Thu, Apr 28, 2016 at 07:03:40PM -0300, Ezequiel Garcia wrote:
> Calling a GPIO LEDs is quite likely to work even if the kernel
> has paniced, so they are ideal to blink in this situation.
> This commit adds support for the new "panic-indicator"
> firmware property, allowing to mark a given LED to blink on
> a kernel panic.
> 
> Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> ---
>  Documentation/devicetree/bindings/leds/leds-gpio.txt | 2 ++

Acked-by: Rob Herring <robh@kernel.org>

>  drivers/leds/leds-gpio.c                             | 4 ++++
>  include/linux/leds.h                                 | 1 +
>  3 files changed, 7 insertions(+)

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

[Jacek Anaszewski]

On 04/29/2016 09:20 AM, Jacek Anaszewski wrote:
> 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.

Since the merge window is imminent, I've addressed those issues by
myself and applied the patch set to the for-next branch
of linux-leds.git.

Thanks,
Jacek Anaszewski

> 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 <ezequiel-30ULvvUtt6G51wMPkGsGjgyUoB5FGQPZ@public.gmane.org>
>> ---
>>   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
>>
>
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Re: [PATCH v3 1/3] leds: triggers: Allow to switch the trigger to "panic" on a kernel panic

[Ezequiel Garcia]

On 6 May 2016 at 06:03, Jacek Anaszewski <j.anaszewski@samsung.com> wrote:
> On 04/29/2016 09:20 AM, Jacek Anaszewski wrote:
>>
>> 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.
>
>
> Since the merge window is imminent, I've addressed those issues by
> myself and applied the patch set to the for-next branch
> of linux-leds.git.
>

Thanks a lot for taking care of this, Jacek!
-- 
Ezequiel García, VanguardiaSur
www.vanguardiasur.com.ar