[v3,1/3] leds: triggers: Allow to switch the trigger to "panic" on a kernel panic
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Message ID 1461881020-13964-2-git-send-email-ezequiel@vanguardiasur.com.ar
State New, archived
Headers show
Series
  • Extend the LED panic trigger
Related show

Commit Message

Ezequiel Garcia April 28, 2016, 10:03 p.m. UTC
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(-)

Comments

Jacek Anaszewski April 29, 2016, 7:20 a.m. UTC | #1
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
>
Jacek Anaszewski May 6, 2016, 9:03 a.m. UTC | #2
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@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
>>
>
Ezequiel Garcia May 6, 2016, 1:05 p.m. UTC | #3
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!
Jacek Anaszewski May 11, 2016, 9:41 a.m. UTC | #4
On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>
>
> On 10/05/16 14:26, Jacek Anaszewski wrote:
>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>
>>>
>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>> Hi Tony,
>>>>
>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>> Hi Jacek,
>>>>>      Thank you for getting back. I updated my kernel to 4.5 and have
>>>>> the
>>>>> updated "led_set_brightness" now.
>>>>>
>>>>> It sets
>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>          led_cdev->blink_brightness = brightness;
>>>>>
>>>>>      The new implementation requires hardware specific drivers to poll
>>>>> for flag change. Shouldn't the led-core driver be calling the hardware
>>>>> specific brightness_set (led_set_brightness_nosleep) irrespective of
>>>>> the
>>>>> blink settings?
>>>>>
>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>> implement
>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>> brightness calls dependent on blink settings?
>>>>
>>>> If your question is still:
>>>>
>>>> "Is there a reason for rejecting brightness change requests when
>>>> either of the blink_delays are set?"
>>>>
>>>> then the answer is: yes, brightness setting is deferred until
>>>> the next timer tick to avoid avoid problems in case we are called
>>>> from hard irq context. It should work fine for software blinking.
>>>
>>>
>>> Sorry, was focused debugging 'hardware accelerated blink' on the driver
>>> I am working on, I missed the software blinking implementation.
>>>
>>>>
>>>> Nonetheless, your question, made it obvious that we have a problem
>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>> implement blink_set op. Is this your use case?
>>>>
>>>
>>> Yes, the brightness requests from user space
>>> (/sys/class/leds/*/brightness) does not get passed to hardware specific
>>> driver via the blink_set implemented, unless led_cdev->flags is polled.
>>>
>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>> both Documentation/leds/leds-class.txt and comment over blink_set() op
>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>
>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>> and your question will be groundless, as changing the blink
>>>> brightness should be impossible by design.
>>>>
>>> In my opinion, disabling blink, when brightness change requested doesn't
>>> sound like the right thing to do. There could be cases in which the
>>> brightness of the blinking LED needs to be changed.
>>
>> It could be accomplished with following sequence:
>>
>> $ echo LED_FULL > brightness //set brightness
>> $ echo "timer" > trigger     //enable blinking with brightness=LED_FULL
>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>
>> The only drawback here would be interfered blinking rhythm while
>> resetting blink brightness. Most drivers that implement blink_set
>> op observe what documentation says and disable blinking when
>> new brightness is set. Unfortunately, led_set_brightness() after
>> modifications doesn't take into account drivers that implement
>> blink_set op. It needs to be fixed, i.e. made compatible with
>> the docs.
>>
>>> Maybe we can let the
>>> hardware driver deal with the blink request if it has implemented
>>> brightness_set? The change below seem to work.
>>>
>>>
>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>
>>> At present hardware implemented brightness is not called
>>> if blink delays are set.
>>>
>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>> ---
>>>   drivers/leds/led-core.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>> index 19e1e60d..02dd0f6 100644
>>> --- a/drivers/leds/led-core.c
>>> +++ b/drivers/leds/led-core.c
>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>> *led_cdev,
>>>       /*
>>>        * In case blinking is on delay brightness setting
>>>        * until the next timer tick.
>>> +     * Or if brightness_set is defined, use the associated
>>> implementation.
>>>        */
>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>> +    if ((!led_cdev->brightness_set) &&
>>
>> s/brightness_set/blink_set/ AFAICT
>>
>> It wouldn't cover all cases as the fact that a driver implements
>> blink_set doesn't necessarily mean that hardware blinking is used
>> for current blinking parameters. There are drivers that resort to
>> using software fallback in case the LED controller device doesn't
>> support requested blink intervals.
>>
>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>> be set after successful execution of blink_set op. It would allow to
>> distinguish between hardware and software blinking modes reliably.
>>
>
> Did you mean something like
>
>
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 19e1e60d..4a8b46d 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev *led_cdev,
>           * until the next timer tick.
>           */
>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
> +               if (led_cdev->brightness_set)
> +                       led_set_brightness_nosleep(led_cdev, brightness);

brightness_set is always initialized, probably you meant blink_set.

> +
> +               if (led_cdev->flags & LED_BLINKING_HW) {
> +                       led_cdev->flags &= ~LED_BLINKING_HW;
> +                       return;
> +               }

The dependencies are quite versatile if we wanted to properly implement
what documentation claims. Setting brightness to any value while
blinking is on should stop blinking. It was so before the commit:

76931edd5 ('leds: fix brightness changing when software blinking is active')

The problem was that timer trigger remained active after stopping
blinking, which led us to changing the semantics on new brightness
set, rather than solving the problem with unregistered trigger.
This was also against documentation claims, which was overlooked.

I tried yesterday to deactivate trigger on brightness set
executed during blinking, but there are circular dependencies,
since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
It is also called from led_trigger_set in the trigger removal path.
Generally it seems non-trivial to enforce current documentation claims
in case of software blinking.

The easiest thing to do now would be changing the semantics, so that 
only setting brightness to LED_OFF would disable the trigger, which
in fact is true since few releases. The problem is that many drivers
that implement hardware blinking resets it on any brightness change.
We would have to left them intact, but apply a new semantics in the
LED core, that would allow for new drivers to just update hardware
blinking brightness upon updating the brightness.

If we followed this path then the LED_BLINKING_HW flag would have to
be set in led_blink_setup() after blink_set op returns 0. Thanks to
that, we could distinguish in led_set_brightness whether hardware
or software blinking is enabled. For !LED_BLINKING_HW case we would
proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
and defer brightness setting until next timer tick. For the opposite
case we wouldn't do anything and let the led_set_brightness_nosleep()
to call the appropriate brightness_set/brightness_set_blocking op.
Old drivers would proceed as currently, by disabling blinking
on brightness change, and new ones could apply new semantics by
changing brightness but leaving hardware blinking active.

I wonder if it would be safe to rely on timer_pending() instead of
introducing LED_BLINKING_HW flag...

>                  /*
>                   * If we need to disable soft blinking delegate this to
> the
>                   * work queue task to avoid problems in case we are called
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index bc1476f..f5fa566 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -48,6 +48,7 @@ struct led_classdev {
>   #define LED_BLINK_DISABLE      (1 << 21)
>   #define LED_SYSFS_DISABLE      (1 << 22)
>   #define LED_DEV_CAP_FLASH      (1 << 23)
> +#define LED_BLINKING_HW        (1 << 24)
>
>          /* Set LED brightness level */
>          /* Must not sleep, use a workqueue if needed */
>
>>
>>> +        (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>           /*
>>>            * If we need to disable soft blinking delegate this to the
>>>            * work queue task to avoid problems in case we are called
>>
>>
>
>
Tony Makkiel May 11, 2016, 1:42 p.m. UTC | #5
On 11/05/16 10:41, Jacek Anaszewski wrote:
> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>
>>
>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>
>>>>
>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>> Hi Tony,
>>>>>
>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>> Hi Jacek,
>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and have
>>>>>> the
>>>>>> updated "led_set_brightness" now.
>>>>>>
>>>>>> It sets
>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>
>>>>>>      The new implementation requires hardware specific drivers to
>>>>>> poll
>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>> hardware
>>>>>> specific brightness_set (led_set_brightness_nosleep) irrespective of
>>>>>> the
>>>>>> blink settings?
>>>>>>
>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>> implement
>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>> brightness calls dependent on blink settings?
>>>>>
>>>>> If your question is still:
>>>>>
>>>>> "Is there a reason for rejecting brightness change requests when
>>>>> either of the blink_delays are set?"
>>>>>
>>>>> then the answer is: yes, brightness setting is deferred until
>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>> from hard irq context. It should work fine for software blinking.
>>>>
>>>>
>>>> Sorry, was focused debugging 'hardware accelerated blink' on the driver
>>>> I am working on, I missed the software blinking implementation.
>>>>
>>>>>
>>>>> Nonetheless, your question, made it obvious that we have a problem
>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>> implement blink_set op. Is this your use case?
>>>>>
>>>>
>>>> Yes, the brightness requests from user space
>>>> (/sys/class/leds/*/brightness) does not get passed to hardware specific
>>>> driver via the blink_set implemented, unless led_cdev->flags is polled.
>>>>
>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>> both Documentation/leds/leds-class.txt and comment over blink_set() op
>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>
>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>> and your question will be groundless, as changing the blink
>>>>> brightness should be impossible by design.
>>>>>
>>>> In my opinion, disabling blink, when brightness change requested
>>>> doesn't
>>>> sound like the right thing to do. There could be cases in which the
>>>> brightness of the blinking LED needs to be changed.
>>>
>>> It could be accomplished with following sequence:
>>>
>>> $ echo LED_FULL > brightness //set brightness
>>> $ echo "timer" > trigger     //enable blinking with brightness=LED_FULL
>>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>
>>> The only drawback here would be interfered blinking rhythm while
>>> resetting blink brightness. Most drivers that implement blink_set
>>> op observe what documentation says and disable blinking when
>>> new brightness is set. Unfortunately, led_set_brightness() after
>>> modifications doesn't take into account drivers that implement
>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>> the docs.
>>>
>>>> Maybe we can let the
>>>> hardware driver deal with the blink request if it has implemented
>>>> brightness_set? The change below seem to work.
>>>>
>>>>
>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>
>>>> At present hardware implemented brightness is not called
>>>> if blink delays are set.
>>>>
>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>> ---
>>>>   drivers/leds/led-core.c | 4 +++-
>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>> index 19e1e60d..02dd0f6 100644
>>>> --- a/drivers/leds/led-core.c
>>>> +++ b/drivers/leds/led-core.c
>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>> *led_cdev,
>>>>       /*
>>>>        * In case blinking is on delay brightness setting
>>>>        * until the next timer tick.
>>>> +     * Or if brightness_set is defined, use the associated
>>>> implementation.
>>>>        */
>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>> +    if ((!led_cdev->brightness_set) &&
>>>
>>> s/brightness_set/blink_set/ AFAICT
>>>
>>> It wouldn't cover all cases as the fact that a driver implements
>>> blink_set doesn't necessarily mean that hardware blinking is used
>>> for current blinking parameters. There are drivers that resort to
>>> using software fallback in case the LED controller device doesn't
>>> support requested blink intervals.
>>>
>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>> be set after successful execution of blink_set op. It would allow to
>>> distinguish between hardware and software blinking modes reliably.
>>>
>>
>> Did you mean something like
>>
>>
>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>> index 19e1e60d..4a8b46d 100644
>> --- a/drivers/leds/led-core.c
>> +++ b/drivers/leds/led-core.c
>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>> *led_cdev,
>>           * until the next timer tick.
>>           */
>>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>> +               if (led_cdev->brightness_set)
>> +                       led_set_brightness_nosleep(led_cdev, brightness);
>
> brightness_set is always initialized, probably you meant blink_set.

Your solution from your last comment below sounds better (so probably 
can skip reading this section).

But no, It was not a mistake. Actually, copied from 
'led_set_brightness_nopm' in case to protect from any drivers which 
doesn't define it. The change should follow existing architecture, and 
was hoping to work for both existing and new drivers.

Existing Chip drivers:  Note, the added brightness_set is called only 
when the blink is active. The flag LED_BLINKING_HW won't be set, either 
because driver is not updated to include the flag, or driver wants 
software fallback to deal with it. The problems I can think of is

-  the software flow will also call brightness_set later when the task 
is serviced. But that is with the same values. So shouldn't make 
difference to the user.

New Drivers with brightness support while blinking:- They set brightness 
and the flag. They wont need the software fallback. If for any reason 
brightness couldn't be set, flag is not set and normal procedure 
applies. Again problem I see here is

-	Additional responsibility on chip drivers to set the flag, if 
successfully managed to set brightness while blink is active. This 
shouldn't be a problem on new drivers, as they might just set the flag 
every time brightness change is requested, irrespective of blink 
settings. If they don't set the flag, it falls back to the software flow 
as in existing architecture.

>
>> +
>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>> +                       return;
>> +               }
>
> The dependencies are quite versatile if we wanted to properly implement
> what documentation claims. Setting brightness to any value while
> blinking is on should stop blinking. It was so before the commit:
>
> 76931edd5 ('leds: fix brightness changing when software blinking is
> active')
>
> The problem was that timer trigger remained active after stopping
> blinking, which led us to changing the semantics on new brightness
> set, rather than solving the problem with unregistered trigger.
> This was also against documentation claims, which was overlooked.
>
> I tried yesterday to deactivate trigger on brightness set
> executed during blinking, but there are circular dependencies,
> since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
> It is also called from led_trigger_set in the trigger removal path.
> Generally it seems non-trivial to enforce current documentation claims
> in case of software blinking.
>
> The easiest thing to do now would be changing the semantics, so that
> only setting brightness to LED_OFF would disable the trigger, which
> in fact is true since few releases. The problem is that many drivers
> that implement hardware blinking resets it on any brightness change.
> We would have to left them intact, but apply a new semantics in the
> LED core, that would allow for new drivers to just update hardware
> blinking brightness upon updating the brightness.
>
> If we followed this path then the LED_BLINKING_HW flag would have to
> be set in led_blink_setup() after blink_set op returns 0. Thanks to
> that, we could distinguish in led_set_brightness whether hardware
> or software blinking is enabled. For !LED_BLINKING_HW case we would
> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
> and defer brightness setting until next timer tick. For the opposite
> case we wouldn't do anything and let the led_set_brightness_nosleep()
> to call the appropriate brightness_set/brightness_set_blocking op.
> Old drivers would proceed as currently, by disabling blinking
> on brightness change, and new ones could apply new semantics by
> changing brightness but leaving hardware blinking active.
>

This sounds better as we do not have to rely on drivers to set the flag 
and does not have the problems mentioned above. I tried the following 
and works for my set up :) .


diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 19e1e60d..3698b67 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev 
*led_cdev,
  {
         if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
             led_cdev->blink_set &&
-           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
+           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
+               led_cdev->flags |= LED_BLINKING_HW;
                 return;
+       }

         /* blink with 1 Hz as default if nothing specified */
         if (!*delay_on && !*delay_off)
@@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev *led_cdev,
          * In case blinking is on delay brightness setting
          * until the next timer tick.
          */
-       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
+       if (!(led_cdev->flags & LED_BLINKING_HW) &&
+           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
                 /*
                  * If we need to disable soft blinking delegate this to the
                  * work queue task to avoid problems in case we are called
diff --git a/include/linux/leds.h b/include/linux/leds.h
index bc1476f..f5fa566 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -48,6 +48,7 @@ struct led_classdev {
  #define LED_BLINK_DISABLE      (1 << 21)
  #define LED_SYSFS_DISABLE      (1 << 22)
  #define LED_DEV_CAP_FLASH      (1 << 23)
+#define LED_BLINKING_HW        (1 << 24)

         /* Set LED brightness level */
         /* Must not sleep, use a workqueue if needed */

> I wonder if it would be safe to rely on timer_pending() instead of
> introducing LED_BLINKING_HW flag...
>
How would that work? I am assuming this has something to do with 
software blink? Does it take hardware blink to account?

>>                  /*
>>                   * If we need to disable soft blinking delegate this to
>> the
>>                   * work queue task to avoid problems in case we are
>> called
>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>> index bc1476f..f5fa566 100644
>> --- a/include/linux/leds.h
>> +++ b/include/linux/leds.h
>> @@ -48,6 +48,7 @@ struct led_classdev {
>>   #define LED_BLINK_DISABLE      (1 << 21)
>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>> +#define LED_BLINKING_HW        (1 << 24)
>>
>>          /* Set LED brightness level */
>>          /* Must not sleep, use a workqueue if needed */
>>
>>>
>>>> +        (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>           /*
>>>>            * If we need to disable soft blinking delegate this to the
>>>>            * work queue task to avoid problems in case we are called
>>>
>>>
>>
>>
>
>
Jacek Anaszewski May 12, 2016, 10:26 a.m. UTC | #6
On 05/11/2016 03:42 PM, Tony Makkiel wrote:
>
>
> On 11/05/16 10:41, Jacek Anaszewski wrote:
>> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>>
>>>
>>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>>
>>>>>
>>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>>> Hi Tony,
>>>>>>
>>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>>> Hi Jacek,
>>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and have
>>>>>>> the
>>>>>>> updated "led_set_brightness" now.
>>>>>>>
>>>>>>> It sets
>>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>>
>>>>>>>      The new implementation requires hardware specific drivers to
>>>>>>> poll
>>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>>> hardware
>>>>>>> specific brightness_set (led_set_brightness_nosleep) irrespective of
>>>>>>> the
>>>>>>> blink settings?
>>>>>>>
>>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>>> implement
>>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>>> brightness calls dependent on blink settings?
>>>>>>
>>>>>> If your question is still:
>>>>>>
>>>>>> "Is there a reason for rejecting brightness change requests when
>>>>>> either of the blink_delays are set?"
>>>>>>
>>>>>> then the answer is: yes, brightness setting is deferred until
>>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>>> from hard irq context. It should work fine for software blinking.
>>>>>
>>>>>
>>>>> Sorry, was focused debugging 'hardware accelerated blink' on the
>>>>> driver
>>>>> I am working on, I missed the software blinking implementation.
>>>>>
>>>>>>
>>>>>> Nonetheless, your question, made it obvious that we have a problem
>>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>>> implement blink_set op. Is this your use case?
>>>>>>
>>>>>
>>>>> Yes, the brightness requests from user space
>>>>> (/sys/class/leds/*/brightness) does not get passed to hardware
>>>>> specific
>>>>> driver via the blink_set implemented, unless led_cdev->flags is
>>>>> polled.
>>>>>
>>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>>> both Documentation/leds/leds-class.txt and comment over
>>>>>> blink_set() op
>>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>>
>>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>>> and your question will be groundless, as changing the blink
>>>>>> brightness should be impossible by design.
>>>>>>
>>>>> In my opinion, disabling blink, when brightness change requested
>>>>> doesn't
>>>>> sound like the right thing to do. There could be cases in which the
>>>>> brightness of the blinking LED needs to be changed.
>>>>
>>>> It could be accomplished with following sequence:
>>>>
>>>> $ echo LED_FULL > brightness //set brightness
>>>> $ echo "timer" > trigger     //enable blinking with brightness=LED_FULL
>>>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>>
>>>> The only drawback here would be interfered blinking rhythm while
>>>> resetting blink brightness. Most drivers that implement blink_set
>>>> op observe what documentation says and disable blinking when
>>>> new brightness is set. Unfortunately, led_set_brightness() after
>>>> modifications doesn't take into account drivers that implement
>>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>>> the docs.
>>>>
>>>>> Maybe we can let the
>>>>> hardware driver deal with the blink request if it has implemented
>>>>> brightness_set? The change below seem to work.
>>>>>
>>>>>
>>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>>
>>>>> At present hardware implemented brightness is not called
>>>>> if blink delays are set.
>>>>>
>>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>>> ---
>>>>>   drivers/leds/led-core.c | 4 +++-
>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>> index 19e1e60d..02dd0f6 100644
>>>>> --- a/drivers/leds/led-core.c
>>>>> +++ b/drivers/leds/led-core.c
>>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>>> *led_cdev,
>>>>>       /*
>>>>>        * In case blinking is on delay brightness setting
>>>>>        * until the next timer tick.
>>>>> +     * Or if brightness_set is defined, use the associated
>>>>> implementation.
>>>>>        */
>>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>> +    if ((!led_cdev->brightness_set) &&
>>>>
>>>> s/brightness_set/blink_set/ AFAICT
>>>>
>>>> It wouldn't cover all cases as the fact that a driver implements
>>>> blink_set doesn't necessarily mean that hardware blinking is used
>>>> for current blinking parameters. There are drivers that resort to
>>>> using software fallback in case the LED controller device doesn't
>>>> support requested blink intervals.
>>>>
>>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>>> be set after successful execution of blink_set op. It would allow to
>>>> distinguish between hardware and software blinking modes reliably.
>>>>
>>>
>>> Did you mean something like
>>>
>>>
>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>> index 19e1e60d..4a8b46d 100644
>>> --- a/drivers/leds/led-core.c
>>> +++ b/drivers/leds/led-core.c
>>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>>> *led_cdev,
>>>           * until the next timer tick.
>>>           */
>>>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>> +               if (led_cdev->brightness_set)
>>> +                       led_set_brightness_nosleep(led_cdev,
>>> brightness);
>>
>> brightness_set is always initialized, probably you meant blink_set.
>
> Your solution from your last comment below sounds better (so probably
> can skip reading this section).
>
> But no, It was not a mistake. Actually, copied from
> 'led_set_brightness_nopm' in case to protect from any drivers which
> doesn't define it. The change should follow existing architecture, and
> was hoping to work for both existing and new drivers.

Right, brightness_set can remain uninitialized while
brightness_set_blocking is provided.

> Existing Chip drivers:  Note, the added brightness_set is called only
> when the blink is active. The flag LED_BLINKING_HW won't be set, either
> because driver is not updated to include the flag, or driver wants
> software fallback to deal with it. The problems I can think of is
>
> -  the software flow will also call brightness_set later when the task
> is serviced. But that is with the same values. So shouldn't make
> difference to the user.
>
> New Drivers with brightness support while blinking:- They set brightness
> and the flag. They wont need the software fallback. If for any reason
> brightness couldn't be set, flag is not set and normal procedure
> applies. Again problem I see here is
>
> -    Additional responsibility on chip drivers to set the flag, if

Ah, now I understand your approach.

> successfully managed to set brightness while blink is active. This
> shouldn't be a problem on new drivers, as they might just set the flag
> every time brightness change is requested, irrespective of blink
> settings. If they don't set the flag, it falls back to the software flow
> as in existing architecture.
>
>>
>>> +
>>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>> +                       return;
>>> +               }
>>
>> The dependencies are quite versatile if we wanted to properly implement
>> what documentation claims. Setting brightness to any value while
>> blinking is on should stop blinking. It was so before the commit:
>>
>> 76931edd5 ('leds: fix brightness changing when software blinking is
>> active')
>>
>> The problem was that timer trigger remained active after stopping
>> blinking, which led us to changing the semantics on new brightness
>> set, rather than solving the problem with unregistered trigger.
>> This was also against documentation claims, which was overlooked.
>>
>> I tried yesterday to deactivate trigger on brightness set
>> executed during blinking, but there are circular dependencies,
>> since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
>> It is also called from led_trigger_set in the trigger removal path.
>> Generally it seems non-trivial to enforce current documentation claims
>> in case of software blinking.
>>
>> The easiest thing to do now would be changing the semantics, so that
>> only setting brightness to LED_OFF would disable the trigger, which
>> in fact is true since few releases. The problem is that many drivers
>> that implement hardware blinking resets it on any brightness change.
>> We would have to left them intact, but apply a new semantics in the
>> LED core, that would allow for new drivers to just update hardware
>> blinking brightness upon updating the brightness.
>>
>> If we followed this path then the LED_BLINKING_HW flag would have to
>> be set in led_blink_setup() after blink_set op returns 0. Thanks to
>> that, we could distinguish in led_set_brightness whether hardware
>> or software blinking is enabled. For !LED_BLINKING_HW case we would
>> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
>> and defer brightness setting until next timer tick. For the opposite
>> case we wouldn't do anything and let the led_set_brightness_nosleep()
>> to call the appropriate brightness_set/brightness_set_blocking op.
>> Old drivers would proceed as currently, by disabling blinking
>> on brightness change, and new ones could apply new semantics by
>> changing brightness but leaving hardware blinking active.
>>
>
> This sounds better as we do not have to rely on drivers to set the flag
> and does not have the problems mentioned above. I tried the following
> and works for my set up :) .
>
>
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 19e1e60d..3698b67 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev
> *led_cdev,
>   {
>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>              led_cdev->blink_set &&
> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
> +               led_cdev->flags |= LED_BLINKING_HW;
>                  return;
> +       }
>
>          /* blink with 1 Hz as default if nothing specified */
>          if (!*delay_on && !*delay_off)
> @@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev *led_cdev,
>           * In case blinking is on delay brightness setting
>           * until the next timer tick.
>           */
> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>                  /*
>                   * If we need to disable soft blinking delegate this to
> the
>                   * work queue task to avoid problems in case we are called

We would have to also clear the flag upon blink deactivation, i.e.
when brightness to be set equals LED_OFF. Existing drivers that
implement blink_set op and deactivate blinking on any brightness set
would have to be modified to clear the LED_BLINKING_HW flag in their
brightness_{set|set_blocking} ops.

> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index bc1476f..f5fa566 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -48,6 +48,7 @@ struct led_classdev {
>   #define LED_BLINK_DISABLE      (1 << 21)
>   #define LED_SYSFS_DISABLE      (1 << 22)
>   #define LED_DEV_CAP_FLASH      (1 << 23)
> +#define LED_BLINKING_HW        (1 << 24)
>
>          /* Set LED brightness level */
>          /* Must not sleep, use a workqueue if needed */
>
>> I wonder if it would be safe to rely on timer_pending() instead of
>> introducing LED_BLINKING_HW flag...
>>
> How would that work? I am assuming this has something to do with
> software blink? Does it take hardware blink to account?

This way we could distinguish between software and hardware blinking.
It wouldn't require modifications in drivers:

-       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
+       if (timer_pending(&led_cdev->blink_timer) &&
+           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
                  /*
                   * If we need to disable soft blinking delegate this

It'd must be verified however if it isn't possible that
led_set_brightness is called when timer is already expired,
between two ticks.

>>>                  /*
>>>                   * If we need to disable soft blinking delegate this to
>>> the
>>>                   * work queue task to avoid problems in case we are
>>> called
>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>> index bc1476f..f5fa566 100644
>>> --- a/include/linux/leds.h
>>> +++ b/include/linux/leds.h
>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>> +#define LED_BLINKING_HW        (1 << 24)
>>>
>>>          /* Set LED brightness level */
>>>          /* Must not sleep, use a workqueue if needed */
>>>
>>>>
>>>>> +        (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>>           /*
>>>>>            * If we need to disable soft blinking delegate this to the
>>>>>            * work queue task to avoid problems in case we are called
>>>>
>>>>
>>>
>>>
>>
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-leds" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
Tony Makkiel May 13, 2016, 2:20 p.m. UTC | #7
On 12/05/16 11:26, Jacek Anaszewski wrote:
> On 05/11/2016 03:42 PM, Tony Makkiel wrote:
>>
>>
>> On 11/05/16 10:41, Jacek Anaszewski wrote:
>>> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>>>
>>>>
>>>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>>>
>>>>>>
>>>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>>>> Hi Tony,
>>>>>>>
>>>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>>>> Hi Jacek,
>>>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and
>>>>>>>> have
>>>>>>>> the
>>>>>>>> updated "led_set_brightness" now.
>>>>>>>>
>>>>>>>> It sets
>>>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>>>
>>>>>>>>      The new implementation requires hardware specific drivers to
>>>>>>>> poll
>>>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>>>> hardware
>>>>>>>> specific brightness_set (led_set_brightness_nosleep)
>>>>>>>> irrespective of
>>>>>>>> the
>>>>>>>> blink settings?
>>>>>>>>
>>>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>>>> implement
>>>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>>>> brightness calls dependent on blink settings?
>>>>>>>
>>>>>>> If your question is still:
>>>>>>>
>>>>>>> "Is there a reason for rejecting brightness change requests when
>>>>>>> either of the blink_delays are set?"
>>>>>>>
>>>>>>> then the answer is: yes, brightness setting is deferred until
>>>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>>>> from hard irq context. It should work fine for software blinking.
>>>>>>
>>>>>>
>>>>>> Sorry, was focused debugging 'hardware accelerated blink' on the
>>>>>> driver
>>>>>> I am working on, I missed the software blinking implementation.
>>>>>>
>>>>>>>
>>>>>>> Nonetheless, your question, made it obvious that we have a problem
>>>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>>>> implement blink_set op. Is this your use case?
>>>>>>>
>>>>>>
>>>>>> Yes, the brightness requests from user space
>>>>>> (/sys/class/leds/*/brightness) does not get passed to hardware
>>>>>> specific
>>>>>> driver via the blink_set implemented, unless led_cdev->flags is
>>>>>> polled.
>>>>>>
>>>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>>>> both Documentation/leds/leds-class.txt and comment over
>>>>>>> blink_set() op
>>>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>>>
>>>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>>>> and your question will be groundless, as changing the blink
>>>>>>> brightness should be impossible by design.
>>>>>>>
>>>>>> In my opinion, disabling blink, when brightness change requested
>>>>>> doesn't
>>>>>> sound like the right thing to do. There could be cases in which the
>>>>>> brightness of the blinking LED needs to be changed.
>>>>>
>>>>> It could be accomplished with following sequence:
>>>>>
>>>>> $ echo LED_FULL > brightness //set brightness
>>>>> $ echo "timer" > trigger     //enable blinking with
>>>>> brightness=LED_FULL
>>>>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>>>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>>>
>>>>> The only drawback here would be interfered blinking rhythm while
>>>>> resetting blink brightness. Most drivers that implement blink_set
>>>>> op observe what documentation says and disable blinking when
>>>>> new brightness is set. Unfortunately, led_set_brightness() after
>>>>> modifications doesn't take into account drivers that implement
>>>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>>>> the docs.
>>>>>
>>>>>> Maybe we can let the
>>>>>> hardware driver deal with the blink request if it has implemented
>>>>>> brightness_set? The change below seem to work.
>>>>>>
>>>>>>
>>>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>>>
>>>>>> At present hardware implemented brightness is not called
>>>>>> if blink delays are set.
>>>>>>
>>>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>>>> ---
>>>>>>   drivers/leds/led-core.c | 4 +++-
>>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>> index 19e1e60d..02dd0f6 100644
>>>>>> --- a/drivers/leds/led-core.c
>>>>>> +++ b/drivers/leds/led-core.c
>>>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>>>> *led_cdev,
>>>>>>       /*
>>>>>>        * In case blinking is on delay brightness setting
>>>>>>        * until the next timer tick.
>>>>>> +     * Or if brightness_set is defined, use the associated
>>>>>> implementation.
>>>>>>        */
>>>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>>> +    if ((!led_cdev->brightness_set) &&
>>>>>
>>>>> s/brightness_set/blink_set/ AFAICT
>>>>>
>>>>> It wouldn't cover all cases as the fact that a driver implements
>>>>> blink_set doesn't necessarily mean that hardware blinking is used
>>>>> for current blinking parameters. There are drivers that resort to
>>>>> using software fallback in case the LED controller device doesn't
>>>>> support requested blink intervals.
>>>>>
>>>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>>>> be set after successful execution of blink_set op. It would allow to
>>>>> distinguish between hardware and software blinking modes reliably.
>>>>>
>>>>
>>>> Did you mean something like
>>>>
>>>>
>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>> index 19e1e60d..4a8b46d 100644
>>>> --- a/drivers/leds/led-core.c
>>>> +++ b/drivers/leds/led-core.c
>>>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>>>> *led_cdev,
>>>>           * until the next timer tick.
>>>>           */
>>>>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>> +               if (led_cdev->brightness_set)
>>>> +                       led_set_brightness_nosleep(led_cdev,
>>>> brightness);
>>>
>>> brightness_set is always initialized, probably you meant blink_set.
>>
>> Your solution from your last comment below sounds better (so probably
>> can skip reading this section).
>>
>> But no, It was not a mistake. Actually, copied from
>> 'led_set_brightness_nopm' in case to protect from any drivers which
>> doesn't define it. The change should follow existing architecture, and
>> was hoping to work for both existing and new drivers.
>
> Right, brightness_set can remain uninitialized while
> brightness_set_blocking is provided.
>
>> Existing Chip drivers:  Note, the added brightness_set is called only
>> when the blink is active. The flag LED_BLINKING_HW won't be set, either
>> because driver is not updated to include the flag, or driver wants
>> software fallback to deal with it. The problems I can think of is
>>
>> -  the software flow will also call brightness_set later when the task
>> is serviced. But that is with the same values. So shouldn't make
>> difference to the user.
>>
>> New Drivers with brightness support while blinking:- They set brightness
>> and the flag. They wont need the software fallback. If for any reason
>> brightness couldn't be set, flag is not set and normal procedure
>> applies. Again problem I see here is
>>
>> -    Additional responsibility on chip drivers to set the flag, if
>
> Ah, now I understand your approach.
>
>> successfully managed to set brightness while blink is active. This
>> shouldn't be a problem on new drivers, as they might just set the flag
>> every time brightness change is requested, irrespective of blink
>> settings. If they don't set the flag, it falls back to the software flow
>> as in existing architecture.
>>
>>>
>>>> +
>>>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>>> +                       return;
>>>> +               }
>>>
>>> The dependencies are quite versatile if we wanted to properly implement
>>> what documentation claims. Setting brightness to any value while
>>> blinking is on should stop blinking. It was so before the commit:
>>>
>>> 76931edd5 ('leds: fix brightness changing when software blinking is
>>> active')
>>>
>>> The problem was that timer trigger remained active after stopping
>>> blinking, which led us to changing the semantics on new brightness
>>> set, rather than solving the problem with unregistered trigger.
>>> This was also against documentation claims, which was overlooked.
>>>
>>> I tried yesterday to deactivate trigger on brightness set
>>> executed during blinking, but there are circular dependencies,
>>> since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
>>> It is also called from led_trigger_set in the trigger removal path.
>>> Generally it seems non-trivial to enforce current documentation claims
>>> in case of software blinking.
>>>
>>> The easiest thing to do now would be changing the semantics, so that
>>> only setting brightness to LED_OFF would disable the trigger, which
>>> in fact is true since few releases. The problem is that many drivers
>>> that implement hardware blinking resets it on any brightness change.
>>> We would have to left them intact, but apply a new semantics in the
>>> LED core, that would allow for new drivers to just update hardware
>>> blinking brightness upon updating the brightness.
>>>
>>> If we followed this path then the LED_BLINKING_HW flag would have to
>>> be set in led_blink_setup() after blink_set op returns 0. Thanks to
>>> that, we could distinguish in led_set_brightness whether hardware
>>> or software blinking is enabled. For !LED_BLINKING_HW case we would
>>> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
>>> and defer brightness setting until next timer tick. For the opposite
>>> case we wouldn't do anything and let the led_set_brightness_nosleep()
>>> to call the appropriate brightness_set/brightness_set_blocking op.
>>> Old drivers would proceed as currently, by disabling blinking
>>> on brightness change, and new ones could apply new semantics by
>>> changing brightness but leaving hardware blinking active.
>>>
>>
>> This sounds better as we do not have to rely on drivers to set the flag
>> and does not have the problems mentioned above. I tried the following
>> and works for my set up :) .
>>
>>
>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>> index 19e1e60d..3698b67 100644
>> --- a/drivers/leds/led-core.c
>> +++ b/drivers/leds/led-core.c
>> @@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev
>> *led_cdev,
>>   {
>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>              led_cdev->blink_set &&
>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>> +               led_cdev->flags |= LED_BLINKING_HW;
>>                  return;
>> +       }
>>
>>          /* blink with 1 Hz as default if nothing specified */
>>          if (!*delay_on && !*delay_off)
>> @@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev
>> *led_cdev,
>>           * In case blinking is on delay brightness setting
>>           * until the next timer tick.
>>           */
>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>                  /*
>>                   * If we need to disable soft blinking delegate this to
>> the
>>                   * work queue task to avoid problems in case we are
>> called
>
> We would have to also clear the flag upon blink deactivation, i.e.
> when brightness to be set equals LED_OFF. Existing drivers that
> implement blink_set op and deactivate blinking on any brightness set
> would have to be modified to clear the LED_BLINKING_HW flag in their
> brightness_{set|set_blocking} ops.
>


diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 19e1e60d..7a15035 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -98,6 +98,9 @@ static void set_brightness_delayed(struct work_struct *ws)
 
led_cdev->delayed_set_value);
         else
                 ret = -ENOTSUPP;
+
+       if (led_cdev->delayed_set_value == LED_OFF)
+               led_cdev->flags &= ~LED_BLINKING_HW;
         if (ret < 0)
                 dev_err(led_cdev->dev,
                         "Setting an LED's brightness failed (%d)\n", ret);
@@ -141,8 +144,10 @@ static void led_blink_setup(struct led_classdev 
*led_cdev,
  {
         if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
             led_cdev->blink_set &&
-           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
+           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
+               led_cdev->flags |= LED_BLINKING_HW;
                 return;
+       }

         /* blink with 1 Hz as default if nothing specified */
         if (!*delay_on && !*delay_off)
@@ -209,7 +214,8 @@ void led_set_brightness(struct led_classdev *led_cdev,
          * In case blinking is on delay brightness setting
          * until the next timer tick.
          */
-       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
+       if (!(led_cdev->flags & LED_BLINKING_HW) &&
+           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
                 /*
                  * If we need to disable soft blinking delegate this to the
                  * work queue task to avoid problems in case we are called
@@ -235,6 +241,8 @@ void led_set_brightness_nopm(struct led_classdev 
*led_cdev,
         /* Use brightness_set op if available, it is guaranteed not to 
sleep */
         if (led_cdev->brightness_set) {
                 led_cdev->brightness_set(led_cdev, value);
+               if (value == LED_OFF)
+                       led_cdev->flags &= ~LED_BLINKING_HW;
                 return;
         }

@@ -267,6 +275,9 @@ int led_set_brightness_sync(struct led_classdev 
*led_cdev,
         if (led_cdev->flags & LED_SUSPENDED)
                 return 0;

+       if (value == LED_OFF)
+               led_cdev->flags &= ~LED_BLINKING_HW;
+
         if (led_cdev->brightness_set_blocking)
                 return led_cdev->brightness_set_blocking(led_cdev,
 
led_cdev->brightness);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index bc1476f..f5fa566 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -48,6 +48,7 @@ struct led_classdev {
  #define LED_BLINK_DISABLE      (1 << 21)
  #define LED_SYSFS_DISABLE      (1 << 22)
  #define LED_DEV_CAP_FLASH      (1 << 23)
+#define LED_BLINKING_HW        (1 << 24)

         /* Set LED brightness level */
         /* Must not sleep, use a workqueue if needed */
~


>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>> index bc1476f..f5fa566 100644
>> --- a/include/linux/leds.h
>> +++ b/include/linux/leds.h
>> @@ -48,6 +48,7 @@ struct led_classdev {
>>   #define LED_BLINK_DISABLE      (1 << 21)
>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>> +#define LED_BLINKING_HW        (1 << 24)
>>
>>          /* Set LED brightness level */
>>          /* Must not sleep, use a workqueue if needed */
>>
>>> I wonder if it would be safe to rely on timer_pending() instead of
>>> introducing LED_BLINKING_HW flag...
>>>
>> How would that work? I am assuming this has something to do with
>> software blink? Does it take hardware blink to account?
>
> This way we could distinguish between software and hardware blinking.
> It wouldn't require modifications in drivers:
>
> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
> +       if (timer_pending(&led_cdev->blink_timer) &&
> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>                   /*
>                    * If we need to disable soft blinking delegate this
>
> It'd must be verified however if it isn't possible that
> led_set_brightness is called when timer is already expired,
> between two ticks.

if blink_set is successful, would work without problem,

When blink_set successful : The timer wont be triggered resulting the 
function to return null all the time. --> No problem here

Software blink : I do not have hardware to actually test this case. I 
tried simulating the case.But going through the code. Following are my 
understanding.

Timer Active (Most of the time) : Work as normal. --> No problem here

Timer Expired :led_set_brightness_nopm called.
- Case in which brightness == LED_OFF, LED will be turned off. 
led_cdev->blink_delay_on and delay_off will retain its value. The timer 
will keep on running. So it will re-enable back blink. --> LED_OFF will 
be ignored.

- Case in which brightness != LED_OFF, new brightness set and resume 
normal operation.  --> No problem here



>
>>>>                  /*
>>>>                   * If we need to disable soft blinking delegate
>>>> this to
>>>> the
>>>>                   * work queue task to avoid problems in case we are
>>>> called
>>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>>> index bc1476f..f5fa566 100644
>>>> --- a/include/linux/leds.h
>>>> +++ b/include/linux/leds.h
>>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>>> +#define LED_BLINKING_HW        (1 << 24)
>>>>
>>>>          /* Set LED brightness level */
>>>>          /* Must not sleep, use a workqueue if needed */
>>>>
>>>>>
>>>>>> +        (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>>>           /*
>>>>>>            * If we need to disable soft blinking delegate this to the
>>>>>>            * work queue task to avoid problems in case we are called
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-leds" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>
>
Jacek Anaszewski May 16, 2016, 9:21 a.m. UTC | #8
Hi Tony,

On 05/13/2016 04:20 PM, Tony Makkiel wrote:
>
>
> On 12/05/16 11:26, Jacek Anaszewski wrote:
>> On 05/11/2016 03:42 PM, Tony Makkiel wrote:
>>>
>>>
>>> On 11/05/16 10:41, Jacek Anaszewski wrote:
>>>> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>>>>
>>>>>
>>>>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>>>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>>>>> Hi Tony,
>>>>>>>>
>>>>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>>>>> Hi Jacek,
>>>>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and
>>>>>>>>> have
>>>>>>>>> the
>>>>>>>>> updated "led_set_brightness" now.
>>>>>>>>>
>>>>>>>>> It sets
>>>>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>>>>
>>>>>>>>>      The new implementation requires hardware specific drivers to
>>>>>>>>> poll
>>>>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>>>>> hardware
>>>>>>>>> specific brightness_set (led_set_brightness_nosleep)
>>>>>>>>> irrespective of
>>>>>>>>> the
>>>>>>>>> blink settings?
>>>>>>>>>
>>>>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>>>>> implement
>>>>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>>>>> brightness calls dependent on blink settings?
>>>>>>>>
>>>>>>>> If your question is still:
>>>>>>>>
>>>>>>>> "Is there a reason for rejecting brightness change requests when
>>>>>>>> either of the blink_delays are set?"
>>>>>>>>
>>>>>>>> then the answer is: yes, brightness setting is deferred until
>>>>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>>>>> from hard irq context. It should work fine for software blinking.
>>>>>>>
>>>>>>>
>>>>>>> Sorry, was focused debugging 'hardware accelerated blink' on the
>>>>>>> driver
>>>>>>> I am working on, I missed the software blinking implementation.
>>>>>>>
>>>>>>>>
>>>>>>>> Nonetheless, your question, made it obvious that we have a problem
>>>>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>>>>> implement blink_set op. Is this your use case?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, the brightness requests from user space
>>>>>>> (/sys/class/leds/*/brightness) does not get passed to hardware
>>>>>>> specific
>>>>>>> driver via the blink_set implemented, unless led_cdev->flags is
>>>>>>> polled.
>>>>>>>
>>>>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>>>>> both Documentation/leds/leds-class.txt and comment over
>>>>>>>> blink_set() op
>>>>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>>>>
>>>>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>>>>> and your question will be groundless, as changing the blink
>>>>>>>> brightness should be impossible by design.
>>>>>>>>
>>>>>>> In my opinion, disabling blink, when brightness change requested
>>>>>>> doesn't
>>>>>>> sound like the right thing to do. There could be cases in which the
>>>>>>> brightness of the blinking LED needs to be changed.
>>>>>>
>>>>>> It could be accomplished with following sequence:
>>>>>>
>>>>>> $ echo LED_FULL > brightness //set brightness
>>>>>> $ echo "timer" > trigger     //enable blinking with
>>>>>> brightness=LED_FULL
>>>>>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>>>>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>>>>
>>>>>> The only drawback here would be interfered blinking rhythm while
>>>>>> resetting blink brightness. Most drivers that implement blink_set
>>>>>> op observe what documentation says and disable blinking when
>>>>>> new brightness is set. Unfortunately, led_set_brightness() after
>>>>>> modifications doesn't take into account drivers that implement
>>>>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>>>>> the docs.
>>>>>>
>>>>>>> Maybe we can let the
>>>>>>> hardware driver deal with the blink request if it has implemented
>>>>>>> brightness_set? The change below seem to work.
>>>>>>>
>>>>>>>
>>>>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>>>>
>>>>>>> At present hardware implemented brightness is not called
>>>>>>> if blink delays are set.
>>>>>>>
>>>>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>>>>> ---
>>>>>>>   drivers/leds/led-core.c | 4 +++-
>>>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>>> index 19e1e60d..02dd0f6 100644
>>>>>>> --- a/drivers/leds/led-core.c
>>>>>>> +++ b/drivers/leds/led-core.c
>>>>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>>>>> *led_cdev,
>>>>>>>       /*
>>>>>>>        * In case blinking is on delay brightness setting
>>>>>>>        * until the next timer tick.
>>>>>>> +     * Or if brightness_set is defined, use the associated
>>>>>>> implementation.
>>>>>>>        */
>>>>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>>>> +    if ((!led_cdev->brightness_set) &&
>>>>>>
>>>>>> s/brightness_set/blink_set/ AFAICT
>>>>>>
>>>>>> It wouldn't cover all cases as the fact that a driver implements
>>>>>> blink_set doesn't necessarily mean that hardware blinking is used
>>>>>> for current blinking parameters. There are drivers that resort to
>>>>>> using software fallback in case the LED controller device doesn't
>>>>>> support requested blink intervals.
>>>>>>
>>>>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>>>>> be set after successful execution of blink_set op. It would allow to
>>>>>> distinguish between hardware and software blinking modes reliably.
>>>>>>
>>>>>
>>>>> Did you mean something like
>>>>>
>>>>>
>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>> index 19e1e60d..4a8b46d 100644
>>>>> --- a/drivers/leds/led-core.c
>>>>> +++ b/drivers/leds/led-core.c
>>>>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>>>>> *led_cdev,
>>>>>           * until the next timer tick.
>>>>>           */
>>>>>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>> +               if (led_cdev->brightness_set)
>>>>> +                       led_set_brightness_nosleep(led_cdev,
>>>>> brightness);
>>>>
>>>> brightness_set is always initialized, probably you meant blink_set.
>>>
>>> Your solution from your last comment below sounds better (so probably
>>> can skip reading this section).
>>>
>>> But no, It was not a mistake. Actually, copied from
>>> 'led_set_brightness_nopm' in case to protect from any drivers which
>>> doesn't define it. The change should follow existing architecture, and
>>> was hoping to work for both existing and new drivers.
>>
>> Right, brightness_set can remain uninitialized while
>> brightness_set_blocking is provided.
>>
>>> Existing Chip drivers:  Note, the added brightness_set is called only
>>> when the blink is active. The flag LED_BLINKING_HW won't be set, either
>>> because driver is not updated to include the flag, or driver wants
>>> software fallback to deal with it. The problems I can think of is
>>>
>>> -  the software flow will also call brightness_set later when the task
>>> is serviced. But that is with the same values. So shouldn't make
>>> difference to the user.
>>>
>>> New Drivers with brightness support while blinking:- They set brightness
>>> and the flag. They wont need the software fallback. If for any reason
>>> brightness couldn't be set, flag is not set and normal procedure
>>> applies. Again problem I see here is
>>>
>>> -    Additional responsibility on chip drivers to set the flag, if
>>
>> Ah, now I understand your approach.
>>
>>> successfully managed to set brightness while blink is active. This
>>> shouldn't be a problem on new drivers, as they might just set the flag
>>> every time brightness change is requested, irrespective of blink
>>> settings. If they don't set the flag, it falls back to the software flow
>>> as in existing architecture.
>>>
>>>>
>>>>> +
>>>>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>>>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>>>> +                       return;
>>>>> +               }
>>>>
>>>> The dependencies are quite versatile if we wanted to properly implement
>>>> what documentation claims. Setting brightness to any value while
>>>> blinking is on should stop blinking. It was so before the commit:
>>>>
>>>> 76931edd5 ('leds: fix brightness changing when software blinking is
>>>> active')
>>>>
>>>> The problem was that timer trigger remained active after stopping
>>>> blinking, which led us to changing the semantics on new brightness
>>>> set, rather than solving the problem with unregistered trigger.
>>>> This was also against documentation claims, which was overlooked.
>>>>
>>>> I tried yesterday to deactivate trigger on brightness set
>>>> executed during blinking, but there are circular dependencies,
>>>> since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
>>>> It is also called from led_trigger_set in the trigger removal path.
>>>> Generally it seems non-trivial to enforce current documentation claims
>>>> in case of software blinking.
>>>>
>>>> The easiest thing to do now would be changing the semantics, so that
>>>> only setting brightness to LED_OFF would disable the trigger, which
>>>> in fact is true since few releases. The problem is that many drivers
>>>> that implement hardware blinking resets it on any brightness change.
>>>> We would have to left them intact, but apply a new semantics in the
>>>> LED core, that would allow for new drivers to just update hardware
>>>> blinking brightness upon updating the brightness.
>>>>
>>>> If we followed this path then the LED_BLINKING_HW flag would have to
>>>> be set in led_blink_setup() after blink_set op returns 0. Thanks to
>>>> that, we could distinguish in led_set_brightness whether hardware
>>>> or software blinking is enabled. For !LED_BLINKING_HW case we would
>>>> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
>>>> and defer brightness setting until next timer tick. For the opposite
>>>> case we wouldn't do anything and let the led_set_brightness_nosleep()
>>>> to call the appropriate brightness_set/brightness_set_blocking op.
>>>> Old drivers would proceed as currently, by disabling blinking
>>>> on brightness change, and new ones could apply new semantics by
>>>> changing brightness but leaving hardware blinking active.
>>>>
>>>
>>> This sounds better as we do not have to rely on drivers to set the flag
>>> and does not have the problems mentioned above. I tried the following
>>> and works for my set up :) .
>>>
>>>
>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>> index 19e1e60d..3698b67 100644
>>> --- a/drivers/leds/led-core.c
>>> +++ b/drivers/leds/led-core.c
>>> @@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev
>>> *led_cdev,
>>>   {
>>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>>              led_cdev->blink_set &&
>>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>>> +               led_cdev->flags |= LED_BLINKING_HW;
>>>                  return;
>>> +       }
>>>
>>>          /* blink with 1 Hz as default if nothing specified */
>>>          if (!*delay_on && !*delay_off)
>>> @@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev
>>> *led_cdev,
>>>           * In case blinking is on delay brightness setting
>>>           * until the next timer tick.
>>>           */
>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>                  /*
>>>                   * If we need to disable soft blinking delegate this to
>>> the
>>>                   * work queue task to avoid problems in case we are
>>> called
>>
>> We would have to also clear the flag upon blink deactivation, i.e.
>> when brightness to be set equals LED_OFF. Existing drivers that
>> implement blink_set op and deactivate blinking on any brightness set
>> would have to be modified to clear the LED_BLINKING_HW flag in their
>> brightness_{set|set_blocking} ops.
>>
>
>
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 19e1e60d..7a15035 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -98,6 +98,9 @@ static void set_brightness_delayed(struct work_struct
> *ws)
>
> led_cdev->delayed_set_value);
>          else
>                  ret = -ENOTSUPP;
> +
> +       if (led_cdev->delayed_set_value == LED_OFF)
> +               led_cdev->flags &= ~LED_BLINKING_HW;
>          if (ret < 0)
>                  dev_err(led_cdev->dev,
>                          "Setting an LED's brightness failed (%d)\n", ret);
> @@ -141,8 +144,10 @@ static void led_blink_setup(struct led_classdev
> *led_cdev,
>   {
>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>              led_cdev->blink_set &&
> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
> +               led_cdev->flags |= LED_BLINKING_HW;
>                  return;
> +       }
>
>          /* blink with 1 Hz as default if nothing specified */
>          if (!*delay_on && !*delay_off)
> @@ -209,7 +214,8 @@ void led_set_brightness(struct led_classdev *led_cdev,
>           * In case blinking is on delay brightness setting
>           * until the next timer tick.
>           */
> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>                  /*
>                   * If we need to disable soft blinking delegate this to
> the
>                   * work queue task to avoid problems in case we are called
> @@ -235,6 +241,8 @@ void led_set_brightness_nopm(struct led_classdev
> *led_cdev,
>          /* Use brightness_set op if available, it is guaranteed not to
> sleep */
>          if (led_cdev->brightness_set) {
>                  led_cdev->brightness_set(led_cdev, value);
> +               if (value == LED_OFF)
> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>                  return;
>          }
>
> @@ -267,6 +275,9 @@ int led_set_brightness_sync(struct led_classdev
> *led_cdev,
>          if (led_cdev->flags & LED_SUSPENDED)
>                  return 0;
>
> +       if (value == LED_OFF)
> +               led_cdev->flags &= ~LED_BLINKING_HW;
> +
>          if (led_cdev->brightness_set_blocking)
>                  return led_cdev->brightness_set_blocking(led_cdev,
>
> led_cdev->brightness);
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index bc1476f..f5fa566 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -48,6 +48,7 @@ struct led_classdev {
>   #define LED_BLINK_DISABLE      (1 << 21)
>   #define LED_SYSFS_DISABLE      (1 << 22)
>   #define LED_DEV_CAP_FLASH      (1 << 23)
> +#define LED_BLINKING_HW        (1 << 24)
>
>          /* Set LED brightness level */
>          /* Must not sleep, use a workqueue if needed */
> ~
>
>
>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>> index bc1476f..f5fa566 100644
>>> --- a/include/linux/leds.h
>>> +++ b/include/linux/leds.h
>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>> +#define LED_BLINKING_HW        (1 << 24)
>>>
>>>          /* Set LED brightness level */
>>>          /* Must not sleep, use a workqueue if needed */
>>>
>>>> I wonder if it would be safe to rely on timer_pending() instead of
>>>> introducing LED_BLINKING_HW flag...
>>>>
>>> How would that work? I am assuming this has something to do with
>>> software blink? Does it take hardware blink to account?
>>
>> This way we could distinguish between software and hardware blinking.
>> It wouldn't require modifications in drivers:
>>
>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>> +       if (timer_pending(&led_cdev->blink_timer) &&
>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>                   /*
>>                    * If we need to disable soft blinking delegate this
>>
>> It'd must be verified however if it isn't possible that
>> led_set_brightness is called when timer is already expired,
>> between two ticks.
>
> if blink_set is successful, would work without problem,
>
> When blink_set successful : The timer wont be triggered resulting the
> function to return null all the time. --> No problem here
>
> Software blink : I do not have hardware to actually test this case. I
> tried simulating the case.But going through the code. Following are my
> understanding.

You can test it by leaving blink_set op uninitialized in your driver.

>
> Timer Active (Most of the time) : Work as normal. --> No problem here
>
> Timer Expired :led_set_brightness_nopm called.
> - Case in which brightness == LED_OFF, LED will be turned off.
> led_cdev->blink_delay_on and delay_off will retain its value. The timer
> will keep on running. So it will re-enable back blink. --> LED_OFF will
> be ignored.
>
> - Case in which brightness != LED_OFF, new brightness set and resume
> normal operation.  --> No problem here
>

Thanks for this analysis. I have a new idea - wouldn't it be more robust
if we added LED_BLINKING_SW flag and set it in led_set_software_blink()?

The line

if (led_cdev->blink_delay_on || led_cdev->blink_delay_off)

in led_set_brightness() could be then changed to

if (led_cdev->flags & LED_BLINK_SW) .

LED_BLINK_SW flag would have to be cleared in led_stop_software_blink()
and in the first two conditions in the led_timer_function().

>
>>
>>>>>                  /*
>>>>>                   * If we need to disable soft blinking delegate
>>>>> this to
>>>>> the
>>>>>                   * work queue task to avoid problems in case we are
>>>>> called
>>>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>>>> index bc1476f..f5fa566 100644
>>>>> --- a/include/linux/leds.h
>>>>> +++ b/include/linux/leds.h
>>>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>>>> +#define LED_BLINKING_HW        (1 << 24)
>>>>>
>>>>>          /* Set LED brightness level */
>>>>>          /* Must not sleep, use a workqueue if needed */
>>>>>
>>>>>>
>>>>>>> +        (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>>>>           /*
>>>>>>>            * If we need to disable soft blinking delegate this to
>>>>>>> the
>>>>>>>            * work queue task to avoid problems in case we are called
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-leds" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>>
>>
>>
>
>
Tony Makkiel May 16, 2016, 1:43 p.m. UTC | #9
On 16/05/16 10:21, Jacek Anaszewski wrote:
> Hi Tony,
>
> On 05/13/2016 04:20 PM, Tony Makkiel wrote:
>>
>>
>> On 12/05/16 11:26, Jacek Anaszewski wrote:
>>> On 05/11/2016 03:42 PM, Tony Makkiel wrote:
>>>>
>>>>
>>>> On 11/05/16 10:41, Jacek Anaszewski wrote:
>>>>> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>>>>>
>>>>>>
>>>>>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>>>>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>>>>>> Hi Tony,
>>>>>>>>>
>>>>>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>>>>>> Hi Jacek,
>>>>>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and
>>>>>>>>>> have
>>>>>>>>>> the
>>>>>>>>>> updated "led_set_brightness" now.
>>>>>>>>>>
>>>>>>>>>> It sets
>>>>>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>>>>>
>>>>>>>>>>      The new implementation requires hardware specific drivers to
>>>>>>>>>> poll
>>>>>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>>>>>> hardware
>>>>>>>>>> specific brightness_set (led_set_brightness_nosleep)
>>>>>>>>>> irrespective of
>>>>>>>>>> the
>>>>>>>>>> blink settings?
>>>>>>>>>>
>>>>>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>>>>>> implement
>>>>>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>>>>>> brightness calls dependent on blink settings?
>>>>>>>>>
>>>>>>>>> If your question is still:
>>>>>>>>>
>>>>>>>>> "Is there a reason for rejecting brightness change requests when
>>>>>>>>> either of the blink_delays are set?"
>>>>>>>>>
>>>>>>>>> then the answer is: yes, brightness setting is deferred until
>>>>>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>>>>>> from hard irq context. It should work fine for software blinking.
>>>>>>>>
>>>>>>>>
>>>>>>>> Sorry, was focused debugging 'hardware accelerated blink' on the
>>>>>>>> driver
>>>>>>>> I am working on, I missed the software blinking implementation.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Nonetheless, your question, made it obvious that we have a problem
>>>>>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>>>>>> implement blink_set op. Is this your use case?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Yes, the brightness requests from user space
>>>>>>>> (/sys/class/leds/*/brightness) does not get passed to hardware
>>>>>>>> specific
>>>>>>>> driver via the blink_set implemented, unless led_cdev->flags is
>>>>>>>> polled.
>>>>>>>>
>>>>>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>>>>>> both Documentation/leds/leds-class.txt and comment over
>>>>>>>>> blink_set() op
>>>>>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>>>>>
>>>>>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>>>>>> and your question will be groundless, as changing the blink
>>>>>>>>> brightness should be impossible by design.
>>>>>>>>>
>>>>>>>> In my opinion, disabling blink, when brightness change requested
>>>>>>>> doesn't
>>>>>>>> sound like the right thing to do. There could be cases in which the
>>>>>>>> brightness of the blinking LED needs to be changed.
>>>>>>>
>>>>>>> It could be accomplished with following sequence:
>>>>>>>
>>>>>>> $ echo LED_FULL > brightness //set brightness
>>>>>>> $ echo "timer" > trigger     //enable blinking with
>>>>>>> brightness=LED_FULL
>>>>>>> $ echo 1 > brightness        //stop blinking and set brightness to 1
>>>>>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>>>>>
>>>>>>> The only drawback here would be interfered blinking rhythm while
>>>>>>> resetting blink brightness. Most drivers that implement blink_set
>>>>>>> op observe what documentation says and disable blinking when
>>>>>>> new brightness is set. Unfortunately, led_set_brightness() after
>>>>>>> modifications doesn't take into account drivers that implement
>>>>>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>>>>>> the docs.
>>>>>>>
>>>>>>>> Maybe we can let the
>>>>>>>> hardware driver deal with the blink request if it has implemented
>>>>>>>> brightness_set? The change below seem to work.
>>>>>>>>
>>>>>>>>
>>>>>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>>>>>
>>>>>>>> At present hardware implemented brightness is not called
>>>>>>>> if blink delays are set.
>>>>>>>>
>>>>>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>>>>>> ---
>>>>>>>>   drivers/leds/led-core.c | 4 +++-
>>>>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>>>> index 19e1e60d..02dd0f6 100644
>>>>>>>> --- a/drivers/leds/led-core.c
>>>>>>>> +++ b/drivers/leds/led-core.c
>>>>>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>>>>>> *led_cdev,
>>>>>>>>       /*
>>>>>>>>        * In case blinking is on delay brightness setting
>>>>>>>>        * until the next timer tick.
>>>>>>>> +     * Or if brightness_set is defined, use the associated
>>>>>>>> implementation.
>>>>>>>>        */
>>>>>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>>>>> +    if ((!led_cdev->brightness_set) &&
>>>>>>>
>>>>>>> s/brightness_set/blink_set/ AFAICT
>>>>>>>
>>>>>>> It wouldn't cover all cases as the fact that a driver implements
>>>>>>> blink_set doesn't necessarily mean that hardware blinking is used
>>>>>>> for current blinking parameters. There are drivers that resort to
>>>>>>> using software fallback in case the LED controller device doesn't
>>>>>>> support requested blink intervals.
>>>>>>>
>>>>>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>>>>>> be set after successful execution of blink_set op. It would allow to
>>>>>>> distinguish between hardware and software blinking modes reliably.
>>>>>>>
>>>>>>
>>>>>> Did you mean something like
>>>>>>
>>>>>>
>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>> index 19e1e60d..4a8b46d 100644
>>>>>> --- a/drivers/leds/led-core.c
>>>>>> +++ b/drivers/leds/led-core.c
>>>>>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>>>>>> *led_cdev,
>>>>>>           * until the next timer tick.
>>>>>>           */
>>>>>>          if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>>> +               if (led_cdev->brightness_set)
>>>>>> +                       led_set_brightness_nosleep(led_cdev,
>>>>>> brightness);
>>>>>
>>>>> brightness_set is always initialized, probably you meant blink_set.
>>>>
>>>> Your solution from your last comment below sounds better (so probably
>>>> can skip reading this section).
>>>>
>>>> But no, It was not a mistake. Actually, copied from
>>>> 'led_set_brightness_nopm' in case to protect from any drivers which
>>>> doesn't define it. The change should follow existing architecture, and
>>>> was hoping to work for both existing and new drivers.
>>>
>>> Right, brightness_set can remain uninitialized while
>>> brightness_set_blocking is provided.
>>>
>>>> Existing Chip drivers:  Note, the added brightness_set is called only
>>>> when the blink is active. The flag LED_BLINKING_HW won't be set, either
>>>> because driver is not updated to include the flag, or driver wants
>>>> software fallback to deal with it. The problems I can think of is
>>>>
>>>> -  the software flow will also call brightness_set later when the task
>>>> is serviced. But that is with the same values. So shouldn't make
>>>> difference to the user.
>>>>
>>>> New Drivers with brightness support while blinking:- They set
>>>> brightness
>>>> and the flag. They wont need the software fallback. If for any reason
>>>> brightness couldn't be set, flag is not set and normal procedure
>>>> applies. Again problem I see here is
>>>>
>>>> -    Additional responsibility on chip drivers to set the flag, if
>>>
>>> Ah, now I understand your approach.
>>>
>>>> successfully managed to set brightness while blink is active. This
>>>> shouldn't be a problem on new drivers, as they might just set the flag
>>>> every time brightness change is requested, irrespective of blink
>>>> settings. If they don't set the flag, it falls back to the software
>>>> flow
>>>> as in existing architecture.
>>>>
>>>>>
>>>>>> +
>>>>>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>>>>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>>>>> +                       return;
>>>>>> +               }
>>>>>
>>>>> The dependencies are quite versatile if we wanted to properly
>>>>> implement
>>>>> what documentation claims. Setting brightness to any value while
>>>>> blinking is on should stop blinking. It was so before the commit:
>>>>>
>>>>> 76931edd5 ('leds: fix brightness changing when software blinking is
>>>>> active')
>>>>>
>>>>> The problem was that timer trigger remained active after stopping
>>>>> blinking, which led us to changing the semantics on new brightness
>>>>> set, rather than solving the problem with unregistered trigger.
>>>>> This was also against documentation claims, which was overlooked.
>>>>>
>>>>> I tried yesterday to deactivate trigger on brightness set
>>>>> executed during blinking, but there are circular dependencies,
>>>>> since led_set_brightness(led_cdev, LED_OFF) is called on deactivation.
>>>>> It is also called from led_trigger_set in the trigger removal path.
>>>>> Generally it seems non-trivial to enforce current documentation claims
>>>>> in case of software blinking.
>>>>>
>>>>> The easiest thing to do now would be changing the semantics, so that
>>>>> only setting brightness to LED_OFF would disable the trigger, which
>>>>> in fact is true since few releases. The problem is that many drivers
>>>>> that implement hardware blinking resets it on any brightness change.
>>>>> We would have to left them intact, but apply a new semantics in the
>>>>> LED core, that would allow for new drivers to just update hardware
>>>>> blinking brightness upon updating the brightness.
>>>>>
>>>>> If we followed this path then the LED_BLINKING_HW flag would have to
>>>>> be set in led_blink_setup() after blink_set op returns 0. Thanks to
>>>>> that, we could distinguish in led_set_brightness whether hardware
>>>>> or software blinking is enabled. For !LED_BLINKING_HW case we would
>>>>> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
>>>>> and defer brightness setting until next timer tick. For the opposite
>>>>> case we wouldn't do anything and let the led_set_brightness_nosleep()
>>>>> to call the appropriate brightness_set/brightness_set_blocking op.
>>>>> Old drivers would proceed as currently, by disabling blinking
>>>>> on brightness change, and new ones could apply new semantics by
>>>>> changing brightness but leaving hardware blinking active.
>>>>>
>>>>
>>>> This sounds better as we do not have to rely on drivers to set the flag
>>>> and does not have the problems mentioned above. I tried the following
>>>> and works for my set up :) .
>>>>
>>>>
>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>> index 19e1e60d..3698b67 100644
>>>> --- a/drivers/leds/led-core.c
>>>> +++ b/drivers/leds/led-core.c
>>>> @@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev
>>>> *led_cdev,
>>>>   {
>>>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>>>              led_cdev->blink_set &&
>>>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>>>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>>>> +               led_cdev->flags |= LED_BLINKING_HW;
>>>>                  return;
>>>> +       }
>>>>
>>>>          /* blink with 1 Hz as default if nothing specified */
>>>>          if (!*delay_on && !*delay_off)
>>>> @@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev
>>>> *led_cdev,
>>>>           * In case blinking is on delay brightness setting
>>>>           * until the next timer tick.
>>>>           */
>>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>                  /*
>>>>                   * If we need to disable soft blinking delegate
>>>> this to
>>>> the
>>>>                   * work queue task to avoid problems in case we are
>>>> called
>>>
>>> We would have to also clear the flag upon blink deactivation, i.e.
>>> when brightness to be set equals LED_OFF. Existing drivers that
>>> implement blink_set op and deactivate blinking on any brightness set
>>> would have to be modified to clear the LED_BLINKING_HW flag in their
>>> brightness_{set|set_blocking} ops.
>>>
>>
>>
>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>> index 19e1e60d..7a15035 100644
>> --- a/drivers/leds/led-core.c
>> +++ b/drivers/leds/led-core.c
>> @@ -98,6 +98,9 @@ static void set_brightness_delayed(struct work_struct
>> *ws)
>>
>> led_cdev->delayed_set_value);
>>          else
>>                  ret = -ENOTSUPP;
>> +
>> +       if (led_cdev->delayed_set_value == LED_OFF)
>> +               led_cdev->flags &= ~LED_BLINKING_HW;
>>          if (ret < 0)
>>                  dev_err(led_cdev->dev,
>>                          "Setting an LED's brightness failed (%d)\n",
>> ret);
>> @@ -141,8 +144,10 @@ static void led_blink_setup(struct led_classdev
>> *led_cdev,
>>   {
>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>              led_cdev->blink_set &&
>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>> +               led_cdev->flags |= LED_BLINKING_HW;
>>                  return;
>> +       }
>>
>>          /* blink with 1 Hz as default if nothing specified */
>>          if (!*delay_on && !*delay_off)
>> @@ -209,7 +214,8 @@ void led_set_brightness(struct led_classdev
>> *led_cdev,
>>           * In case blinking is on delay brightness setting
>>           * until the next timer tick.
>>           */
>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>                  /*
>>                   * If we need to disable soft blinking delegate this to
>> the
>>                   * work queue task to avoid problems in case we are
>> called
>> @@ -235,6 +241,8 @@ void led_set_brightness_nopm(struct led_classdev
>> *led_cdev,
>>          /* Use brightness_set op if available, it is guaranteed not to
>> sleep */
>>          if (led_cdev->brightness_set) {
>>                  led_cdev->brightness_set(led_cdev, value);
>> +               if (value == LED_OFF)
>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>                  return;
>>          }
>>
>> @@ -267,6 +275,9 @@ int led_set_brightness_sync(struct led_classdev
>> *led_cdev,
>>          if (led_cdev->flags & LED_SUSPENDED)
>>                  return 0;
>>
>> +       if (value == LED_OFF)
>> +               led_cdev->flags &= ~LED_BLINKING_HW;
>> +
>>          if (led_cdev->brightness_set_blocking)
>>                  return led_cdev->brightness_set_blocking(led_cdev,
>>
>> led_cdev->brightness);
>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>> index bc1476f..f5fa566 100644
>> --- a/include/linux/leds.h
>> +++ b/include/linux/leds.h
>> @@ -48,6 +48,7 @@ struct led_classdev {
>>   #define LED_BLINK_DISABLE      (1 << 21)
>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>> +#define LED_BLINKING_HW        (1 << 24)
>>
>>          /* Set LED brightness level */
>>          /* Must not sleep, use a workqueue if needed */
>> ~
>>
>>
>>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>>> index bc1476f..f5fa566 100644
>>>> --- a/include/linux/leds.h
>>>> +++ b/include/linux/leds.h
>>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>>> +#define LED_BLINKING_HW        (1 << 24)
>>>>
>>>>          /* Set LED brightness level */
>>>>          /* Must not sleep, use a workqueue if needed */
>>>>
>>>>> I wonder if it would be safe to rely on timer_pending() instead of
>>>>> introducing LED_BLINKING_HW flag...
>>>>>
>>>> How would that work? I am assuming this has something to do with
>>>> software blink? Does it take hardware blink to account?
>>>
>>> This way we could distinguish between software and hardware blinking.
>>> It wouldn't require modifications in drivers:
>>>
>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>> +       if (timer_pending(&led_cdev->blink_timer) &&
>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>                   /*
>>>                    * If we need to disable soft blinking delegate this
>>>
>>> It'd must be verified however if it isn't possible that
>>> led_set_brightness is called when timer is already expired,
>>> between two ticks.
>>
>> if blink_set is successful, would work without problem,
>>
>> When blink_set successful : The timer wont be triggered resulting the
>> function to return null all the time. --> No problem here
>>
>> Software blink : I do not have hardware to actually test this case. I
>> tried simulating the case.But going through the code. Following are my
>> understanding.
>
> You can test it by leaving blink_set op uninitialized in your driver.
>
>>
>> Timer Active (Most of the time) : Work as normal. --> No problem here
>>
>> Timer Expired :led_set_brightness_nopm called.
>> - Case in which brightness == LED_OFF, LED will be turned off.
>> led_cdev->blink_delay_on and delay_off will retain its value. The timer
>> will keep on running. So it will re-enable back blink. --> LED_OFF will
>> be ignored.
>>
>> - Case in which brightness != LED_OFF, new brightness set and resume
>> normal operation.  --> No problem here
>>
>
> Thanks for this analysis. I have a new idea - wouldn't it be more robust
> if we added LED_BLINKING_SW flag and set it in led_set_software_blink()?
>
> The line
>
> if (led_cdev->blink_delay_on || led_cdev->blink_delay_off)
>
> in led_set_brightness() could be then changed to
>
> if (led_cdev->flags & LED_BLINK_SW) .
>
> LED_BLINK_SW flag would have to be cleared in led_stop_software_blink()
> and in the first two conditions in the led_timer_function().
>

Yes, that will do with minimal changes. I tested the following, and works.

Date: Mon, 16 May 2016 14:18:42 +0100
Subject: [PATCH 1/1]  Allow chip-driver to set brightness if, software 
blink not used.

If software blink were active any brightness change request
  were not sent to the chip driver.

Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
---
  drivers/leds/led-core.c | 7 +++++--
  include/linux/leds.h    | 1 +
  2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 19e1e60d..376b5ea 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -33,11 +33,12 @@ static void led_timer_function(unsigned long data)

  	if (!led_cdev->blink_delay_on || !led_cdev->blink_delay_off) {
  		led_set_brightness_nosleep(led_cdev, LED_OFF);
+		led_cdev->flags &= ~LED_BLINKING_SW;
  		return;
  	}

  	if (led_cdev->flags & LED_BLINK_ONESHOT_STOP) {
-		led_cdev->flags &= ~LED_BLINK_ONESHOT_STOP;
+		led_cdev->flags &= ~(LED_BLINK_ONESHOT_STOP | LED_BLINKING_SW);
  		return;
  	}

@@ -131,6 +132,7 @@ static void led_set_software_blink(struct 
led_classdev *led_cdev,
  		return;
  	}

+	led_cdev->flags |= LED_BLINKING_SW;
  	mod_timer(&led_cdev->blink_timer, jiffies + 1);
  }

@@ -199,6 +201,7 @@ void led_stop_software_blink(struct led_classdev 
*led_cdev)
  	del_timer_sync(&led_cdev->blink_timer);
  	led_cdev->blink_delay_on = 0;
  	led_cdev->blink_delay_off = 0;
+	led_cdev->flags &= ~LED_BLINKING_SW;
  }
  EXPORT_SYMBOL_GPL(led_stop_software_blink);

@@ -209,7 +212,7 @@ void led_set_brightness(struct led_classdev *led_cdev,
  	 * In case blinking is on delay brightness setting
  	 * until the next timer tick.
  	 */
-	if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
+	if (led_cdev->flags & LED_BLINKING_SW) {
  		/*
  		 * If we need to disable soft blinking delegate this to the
  		 * work queue task to avoid problems in case we are called
diff --git a/include/linux/leds.h b/include/linux/leds.h
index bc1476f..08ef6f4 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -48,6 +48,7 @@ struct led_classdev {
  #define LED_BLINK_DISABLE	(1 << 21)
  #define LED_SYSFS_DISABLE	(1 << 22)
  #define LED_DEV_CAP_FLASH	(1 << 23)
+#define LED_BLINKING_SW 	(1 << 24)

  	/* Set LED brightness level */
  	/* Must not sleep, use a workqueue if needed */
Jacek Anaszewski May 16, 2016, 2:23 p.m. UTC | #10
On 05/16/2016 03:43 PM, Tony Makkiel wrote:
>
>
> On 16/05/16 10:21, Jacek Anaszewski wrote:
>> Hi Tony,
>>
>> On 05/13/2016 04:20 PM, Tony Makkiel wrote:
>>>
>>>
>>> On 12/05/16 11:26, Jacek Anaszewski wrote:
>>>> On 05/11/2016 03:42 PM, Tony Makkiel wrote:
>>>>>
>>>>>
>>>>> On 11/05/16 10:41, Jacek Anaszewski wrote:
>>>>>> On 05/10/2016 06:55 PM, Tony Makkiel wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 10/05/16 14:26, Jacek Anaszewski wrote:
>>>>>>>> On 05/10/2016 11:36 AM, Tony Makkiel wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 09/05/16 15:45, Jacek Anaszewski wrote:
>>>>>>>>>> Hi Tony,
>>>>>>>>>>
>>>>>>>>>> On 05/09/2016 03:27 PM, Tony Makkiel wrote:
>>>>>>>>>>> Hi Jacek,
>>>>>>>>>>>      Thank you for getting back. I updated my kernel to 4.5 and
>>>>>>>>>>> have
>>>>>>>>>>> the
>>>>>>>>>>> updated "led_set_brightness" now.
>>>>>>>>>>>
>>>>>>>>>>> It sets
>>>>>>>>>>>          led_cdev->flags |= LED_BLINK_BRIGHTNESS_CHANGE;
>>>>>>>>>>>          led_cdev->blink_brightness = brightness;
>>>>>>>>>>>
>>>>>>>>>>>      The new implementation requires hardware specific
>>>>>>>>>>> drivers to
>>>>>>>>>>> poll
>>>>>>>>>>> for flag change. Shouldn't the led-core driver be calling the
>>>>>>>>>>> hardware
>>>>>>>>>>> specific brightness_set (led_set_brightness_nosleep)
>>>>>>>>>>> irrespective of
>>>>>>>>>>> the
>>>>>>>>>>> blink settings?
>>>>>>>>>>>
>>>>>>>>>>> Unfortunately, it place additional requirement on drivers, to
>>>>>>>>>>> implement
>>>>>>>>>>> a polling mechanism which won't be needed otherwise. Why are the
>>>>>>>>>>> brightness calls dependent on blink settings?
>>>>>>>>>>
>>>>>>>>>> If your question is still:
>>>>>>>>>>
>>>>>>>>>> "Is there a reason for rejecting brightness change requests when
>>>>>>>>>> either of the blink_delays are set?"
>>>>>>>>>>
>>>>>>>>>> then the answer is: yes, brightness setting is deferred until
>>>>>>>>>> the next timer tick to avoid avoid problems in case we are called
>>>>>>>>>> from hard irq context. It should work fine for software blinking.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Sorry, was focused debugging 'hardware accelerated blink' on the
>>>>>>>>> driver
>>>>>>>>> I am working on, I missed the software blinking implementation.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Nonetheless, your question, made it obvious that we have a
>>>>>>>>>> problem
>>>>>>>>>> here in case of hardware accelerated blinking, i.e. drivers that
>>>>>>>>>> implement blink_set op. Is this your use case?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Yes, the brightness requests from user space
>>>>>>>>> (/sys/class/leds/*/brightness) does not get passed to hardware
>>>>>>>>> specific
>>>>>>>>> driver via the blink_set implemented, unless led_cdev->flags is
>>>>>>>>> polled.
>>>>>>>>>
>>>>>>>>>> Anyway, I've noticed a discrepancy between the LED core code and
>>>>>>>>>> both Documentation/leds/leds-class.txt and comment over
>>>>>>>>>> blink_set() op
>>>>>>>>>> in include/linux/leds.h, which say that blinking is deactivated
>>>>>>>>>> upon setting the brightness again. Many drivers apply this rule.
>>>>>>>>>>
>>>>>>>>>> In effect, LED_BLINK_BRIGHTNESS_CHANGE will have to be removed,
>>>>>>>>>> and your question will be groundless, as changing the blink
>>>>>>>>>> brightness should be impossible by design.
>>>>>>>>>>
>>>>>>>>> In my opinion, disabling blink, when brightness change requested
>>>>>>>>> doesn't
>>>>>>>>> sound like the right thing to do. There could be cases in which
>>>>>>>>> the
>>>>>>>>> brightness of the blinking LED needs to be changed.
>>>>>>>>
>>>>>>>> It could be accomplished with following sequence:
>>>>>>>>
>>>>>>>> $ echo LED_FULL > brightness //set brightness
>>>>>>>> $ echo "timer" > trigger     //enable blinking with
>>>>>>>> brightness=LED_FULL
>>>>>>>> $ echo 1 > brightness        //stop blinking and set brightness
>>>>>>>> to 1
>>>>>>>> $ echo "timer" > trigger     //enable blinking with brightness=1
>>>>>>>>
>>>>>>>> The only drawback here would be interfered blinking rhythm while
>>>>>>>> resetting blink brightness. Most drivers that implement blink_set
>>>>>>>> op observe what documentation says and disable blinking when
>>>>>>>> new brightness is set. Unfortunately, led_set_brightness() after
>>>>>>>> modifications doesn't take into account drivers that implement
>>>>>>>> blink_set op. It needs to be fixed, i.e. made compatible with
>>>>>>>> the docs.
>>>>>>>>
>>>>>>>>> Maybe we can let the
>>>>>>>>> hardware driver deal with the blink request if it has implemented
>>>>>>>>> brightness_set? The change below seem to work.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Subject: [PATCH] led-core: Use hardware blink when available
>>>>>>>>>
>>>>>>>>> At present hardware implemented brightness is not called
>>>>>>>>> if blink delays are set.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
>>>>>>>>> ---
>>>>>>>>>   drivers/leds/led-core.c | 4 +++-
>>>>>>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>>>>> index 19e1e60d..02dd0f6 100644
>>>>>>>>> --- a/drivers/leds/led-core.c
>>>>>>>>> +++ b/drivers/leds/led-core.c
>>>>>>>>> @@ -208,8 +208,10 @@ void led_set_brightness(struct led_classdev
>>>>>>>>> *led_cdev,
>>>>>>>>>       /*
>>>>>>>>>        * In case blinking is on delay brightness setting
>>>>>>>>>        * until the next timer tick.
>>>>>>>>> +     * Or if brightness_set is defined, use the associated
>>>>>>>>> implementation.
>>>>>>>>>        */
>>>>>>>>> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>>>>>> +    if ((!led_cdev->brightness_set) &&
>>>>>>>>
>>>>>>>> s/brightness_set/blink_set/ AFAICT
>>>>>>>>
>>>>>>>> It wouldn't cover all cases as the fact that a driver implements
>>>>>>>> blink_set doesn't necessarily mean that hardware blinking is used
>>>>>>>> for current blinking parameters. There are drivers that resort to
>>>>>>>> using software fallback in case the LED controller device doesn't
>>>>>>>> support requested blink intervals.
>>>>>>>>
>>>>>>>> I'm planning on addition of a LED_BLINKING_HW flag, that would
>>>>>>>> be set after successful execution of blink_set op. It would
>>>>>>>> allow to
>>>>>>>> distinguish between hardware and software blinking modes reliably.
>>>>>>>>
>>>>>>>
>>>>>>> Did you mean something like
>>>>>>>
>>>>>>>
>>>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>>>> index 19e1e60d..4a8b46d 100644
>>>>>>> --- a/drivers/leds/led-core.c
>>>>>>> +++ b/drivers/leds/led-core.c
>>>>>>> @@ -210,6 +210,13 @@ void led_set_brightness(struct led_classdev
>>>>>>> *led_cdev,
>>>>>>>           * until the next timer tick.
>>>>>>>           */
>>>>>>>          if (led_cdev->blink_delay_on ||
>>>>>>> led_cdev->blink_delay_off) {
>>>>>>> +               if (led_cdev->brightness_set)
>>>>>>> +                       led_set_brightness_nosleep(led_cdev,
>>>>>>> brightness);
>>>>>>
>>>>>> brightness_set is always initialized, probably you meant blink_set.
>>>>>
>>>>> Your solution from your last comment below sounds better (so probably
>>>>> can skip reading this section).
>>>>>
>>>>> But no, It was not a mistake. Actually, copied from
>>>>> 'led_set_brightness_nopm' in case to protect from any drivers which
>>>>> doesn't define it. The change should follow existing architecture, and
>>>>> was hoping to work for both existing and new drivers.
>>>>
>>>> Right, brightness_set can remain uninitialized while
>>>> brightness_set_blocking is provided.
>>>>
>>>>> Existing Chip drivers:  Note, the added brightness_set is called only
>>>>> when the blink is active. The flag LED_BLINKING_HW won't be set,
>>>>> either
>>>>> because driver is not updated to include the flag, or driver wants
>>>>> software fallback to deal with it. The problems I can think of is
>>>>>
>>>>> -  the software flow will also call brightness_set later when the task
>>>>> is serviced. But that is with the same values. So shouldn't make
>>>>> difference to the user.
>>>>>
>>>>> New Drivers with brightness support while blinking:- They set
>>>>> brightness
>>>>> and the flag. They wont need the software fallback. If for any reason
>>>>> brightness couldn't be set, flag is not set and normal procedure
>>>>> applies. Again problem I see here is
>>>>>
>>>>> -    Additional responsibility on chip drivers to set the flag, if
>>>>
>>>> Ah, now I understand your approach.
>>>>
>>>>> successfully managed to set brightness while blink is active. This
>>>>> shouldn't be a problem on new drivers, as they might just set the flag
>>>>> every time brightness change is requested, irrespective of blink
>>>>> settings. If they don't set the flag, it falls back to the software
>>>>> flow
>>>>> as in existing architecture.
>>>>>
>>>>>>
>>>>>>> +
>>>>>>> +               if (led_cdev->flags & LED_BLINKING_HW) {
>>>>>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>>>>>> +                       return;
>>>>>>> +               }
>>>>>>
>>>>>> The dependencies are quite versatile if we wanted to properly
>>>>>> implement
>>>>>> what documentation claims. Setting brightness to any value while
>>>>>> blinking is on should stop blinking. It was so before the commit:
>>>>>>
>>>>>> 76931edd5 ('leds: fix brightness changing when software blinking is
>>>>>> active')
>>>>>>
>>>>>> The problem was that timer trigger remained active after stopping
>>>>>> blinking, which led us to changing the semantics on new brightness
>>>>>> set, rather than solving the problem with unregistered trigger.
>>>>>> This was also against documentation claims, which was overlooked.
>>>>>>
>>>>>> I tried yesterday to deactivate trigger on brightness set
>>>>>> executed during blinking, but there are circular dependencies,
>>>>>> since led_set_brightness(led_cdev, LED_OFF) is called on
>>>>>> deactivation.
>>>>>> It is also called from led_trigger_set in the trigger removal path.
>>>>>> Generally it seems non-trivial to enforce current documentation
>>>>>> claims
>>>>>> in case of software blinking.
>>>>>>
>>>>>> The easiest thing to do now would be changing the semantics, so that
>>>>>> only setting brightness to LED_OFF would disable the trigger, which
>>>>>> in fact is true since few releases. The problem is that many drivers
>>>>>> that implement hardware blinking resets it on any brightness change.
>>>>>> We would have to left them intact, but apply a new semantics in the
>>>>>> LED core, that would allow for new drivers to just update hardware
>>>>>> blinking brightness upon updating the brightness.
>>>>>>
>>>>>> If we followed this path then the LED_BLINKING_HW flag would have to
>>>>>> be set in led_blink_setup() after blink_set op returns 0. Thanks to
>>>>>> that, we could distinguish in led_set_brightness whether hardware
>>>>>> or software blinking is enabled. For !LED_BLINKING_HW case we would
>>>>>> proceed as currently, i.e. set the LED_BLINK_BRIGHTNESS_CHANGE flag
>>>>>> and defer brightness setting until next timer tick. For the opposite
>>>>>> case we wouldn't do anything and let the led_set_brightness_nosleep()
>>>>>> to call the appropriate brightness_set/brightness_set_blocking op.
>>>>>> Old drivers would proceed as currently, by disabling blinking
>>>>>> on brightness change, and new ones could apply new semantics by
>>>>>> changing brightness but leaving hardware blinking active.
>>>>>>
>>>>>
>>>>> This sounds better as we do not have to rely on drivers to set the
>>>>> flag
>>>>> and does not have the problems mentioned above. I tried the following
>>>>> and works for my set up :) .
>>>>>
>>>>>
>>>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>>>> index 19e1e60d..3698b67 100644
>>>>> --- a/drivers/leds/led-core.c
>>>>> +++ b/drivers/leds/led-core.c
>>>>> @@ -141,8 +141,10 @@ static void led_blink_setup(struct led_classdev
>>>>> *led_cdev,
>>>>>   {
>>>>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>>>>              led_cdev->blink_set &&
>>>>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>>>>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>>>>> +               led_cdev->flags |= LED_BLINKING_HW;
>>>>>                  return;
>>>>> +       }
>>>>>
>>>>>          /* blink with 1 Hz as default if nothing specified */
>>>>>          if (!*delay_on && !*delay_off)
>>>>> @@ -209,7 +211,8 @@ void led_set_brightness(struct led_classdev
>>>>> *led_cdev,
>>>>>           * In case blinking is on delay brightness setting
>>>>>           * until the next timer tick.
>>>>>           */
>>>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>>>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>>                  /*
>>>>>                   * If we need to disable soft blinking delegate
>>>>> this to
>>>>> the
>>>>>                   * work queue task to avoid problems in case we are
>>>>> called
>>>>
>>>> We would have to also clear the flag upon blink deactivation, i.e.
>>>> when brightness to be set equals LED_OFF. Existing drivers that
>>>> implement blink_set op and deactivate blinking on any brightness set
>>>> would have to be modified to clear the LED_BLINKING_HW flag in their
>>>> brightness_{set|set_blocking} ops.
>>>>
>>>
>>>
>>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>>> index 19e1e60d..7a15035 100644
>>> --- a/drivers/leds/led-core.c
>>> +++ b/drivers/leds/led-core.c
>>> @@ -98,6 +98,9 @@ static void set_brightness_delayed(struct work_struct
>>> *ws)
>>>
>>> led_cdev->delayed_set_value);
>>>          else
>>>                  ret = -ENOTSUPP;
>>> +
>>> +       if (led_cdev->delayed_set_value == LED_OFF)
>>> +               led_cdev->flags &= ~LED_BLINKING_HW;
>>>          if (ret < 0)
>>>                  dev_err(led_cdev->dev,
>>>                          "Setting an LED's brightness failed (%d)\n",
>>> ret);
>>> @@ -141,8 +144,10 @@ static void led_blink_setup(struct led_classdev
>>> *led_cdev,
>>>   {
>>>          if (!(led_cdev->flags & LED_BLINK_ONESHOT) &&
>>>              led_cdev->blink_set &&
>>> -           !led_cdev->blink_set(led_cdev, delay_on, delay_off))
>>> +           !led_cdev->blink_set(led_cdev, delay_on, delay_off)){
>>> +               led_cdev->flags |= LED_BLINKING_HW;
>>>                  return;
>>> +       }
>>>
>>>          /* blink with 1 Hz as default if nothing specified */
>>>          if (!*delay_on && !*delay_off)
>>> @@ -209,7 +214,8 @@ void led_set_brightness(struct led_classdev
>>> *led_cdev,
>>>           * In case blinking is on delay brightness setting
>>>           * until the next timer tick.
>>>           */
>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>> +       if (!(led_cdev->flags & LED_BLINKING_HW) &&
>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>                  /*
>>>                   * If we need to disable soft blinking delegate this to
>>> the
>>>                   * work queue task to avoid problems in case we are
>>> called
>>> @@ -235,6 +241,8 @@ void led_set_brightness_nopm(struct led_classdev
>>> *led_cdev,
>>>          /* Use brightness_set op if available, it is guaranteed not to
>>> sleep */
>>>          if (led_cdev->brightness_set) {
>>>                  led_cdev->brightness_set(led_cdev, value);
>>> +               if (value == LED_OFF)
>>> +                       led_cdev->flags &= ~LED_BLINKING_HW;
>>>                  return;
>>>          }
>>>
>>> @@ -267,6 +275,9 @@ int led_set_brightness_sync(struct led_classdev
>>> *led_cdev,
>>>          if (led_cdev->flags & LED_SUSPENDED)
>>>                  return 0;
>>>
>>> +       if (value == LED_OFF)
>>> +               led_cdev->flags &= ~LED_BLINKING_HW;
>>> +
>>>          if (led_cdev->brightness_set_blocking)
>>>                  return led_cdev->brightness_set_blocking(led_cdev,
>>>
>>> led_cdev->brightness);
>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>> index bc1476f..f5fa566 100644
>>> --- a/include/linux/leds.h
>>> +++ b/include/linux/leds.h
>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>> +#define LED_BLINKING_HW        (1 << 24)
>>>
>>>          /* Set LED brightness level */
>>>          /* Must not sleep, use a workqueue if needed */
>>> ~
>>>
>>>
>>>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>>>> index bc1476f..f5fa566 100644
>>>>> --- a/include/linux/leds.h
>>>>> +++ b/include/linux/leds.h
>>>>> @@ -48,6 +48,7 @@ struct led_classdev {
>>>>>   #define LED_BLINK_DISABLE      (1 << 21)
>>>>>   #define LED_SYSFS_DISABLE      (1 << 22)
>>>>>   #define LED_DEV_CAP_FLASH      (1 << 23)
>>>>> +#define LED_BLINKING_HW        (1 << 24)
>>>>>
>>>>>          /* Set LED brightness level */
>>>>>          /* Must not sleep, use a workqueue if needed */
>>>>>
>>>>>> I wonder if it would be safe to rely on timer_pending() instead of
>>>>>> introducing LED_BLINKING_HW flag...
>>>>>>
>>>>> How would that work? I am assuming this has something to do with
>>>>> software blink? Does it take hardware blink to account?
>>>>
>>>> This way we could distinguish between software and hardware blinking.
>>>> It wouldn't require modifications in drivers:
>>>>
>>>> -       if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
>>>> +       if (timer_pending(&led_cdev->blink_timer) &&
>>>> +           (led_cdev->blink_delay_on || led_cdev->blink_delay_off)) {
>>>>                   /*
>>>>                    * If we need to disable soft blinking delegate this
>>>>
>>>> It'd must be verified however if it isn't possible that
>>>> led_set_brightness is called when timer is already expired,
>>>> between two ticks.
>>>
>>> if blink_set is successful, would work without problem,
>>>
>>> When blink_set successful : The timer wont be triggered resulting the
>>> function to return null all the time. --> No problem here
>>>
>>> Software blink : I do not have hardware to actually test this case. I
>>> tried simulating the case.But going through the code. Following are my
>>> understanding.
>>
>> You can test it by leaving blink_set op uninitialized in your driver.
>>
>>>
>>> Timer Active (Most of the time) : Work as normal. --> No problem here
>>>
>>> Timer Expired :led_set_brightness_nopm called.
>>> - Case in which brightness == LED_OFF, LED will be turned off.
>>> led_cdev->blink_delay_on and delay_off will retain its value. The timer
>>> will keep on running. So it will re-enable back blink. --> LED_OFF will
>>> be ignored.
>>>
>>> - Case in which brightness != LED_OFF, new brightness set and resume
>>> normal operation.  --> No problem here
>>>
>>
>> Thanks for this analysis. I have a new idea - wouldn't it be more robust
>> if we added LED_BLINKING_SW flag and set it in led_set_software_blink()?
>>
>> The line
>>
>> if (led_cdev->blink_delay_on || led_cdev->blink_delay_off)
>>
>> in led_set_brightness() could be then changed to
>>
>> if (led_cdev->flags & LED_BLINK_SW) .
>>
>> LED_BLINK_SW flag would have to be cleared in led_stop_software_blink()
>> and in the first two conditions in the led_timer_function().
>>
>
> Yes, that will do with minimal changes. I tested the following, and works.

Fine, so could you please submit the patch officially?
Before that, please rebase your code on top of LED tree or linux-next
and change LED_BLINKING_SW to LED_BLINK_SW, to keep the same prefix for
each blinking related definition.

> Date: Mon, 16 May 2016 14:18:42 +0100
> Subject: [PATCH 1/1]  Allow chip-driver to set brightness if, software
> blink not used.
>
> If software blink were active any brightness change request
>   were not sent to the chip driver.
>
> Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
> ---
>   drivers/leds/led-core.c | 7 +++++--
>   include/linux/leds.h    | 1 +
>   2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 19e1e60d..376b5ea 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -33,11 +33,12 @@ static void led_timer_function(unsigned long data)
>
>       if (!led_cdev->blink_delay_on || !led_cdev->blink_delay_off) {
>           led_set_brightness_nosleep(led_cdev, LED_OFF);
> +        led_cdev->flags &= ~LED_BLINKING_SW;
>           return;
>       }
>
>       if (led_cdev->flags & LED_BLINK_ONESHOT_STOP) {
> -        led_cdev->flags &= ~LED_BLINK_ONESHOT_STOP;
> +        led_cdev->flags &= ~(LED_BLINK_ONESHOT_STOP | LED_BLINKING_SW);
>           return;
>       }
>
> @@ -131,6 +132,7 @@ static void led_set_software_blink(struct
> led_classdev *led_cdev,
>           return;
>       }
>
> +    led_cdev->flags |= LED_BLINKING_SW;
>       mod_timer(&led_cdev->blink_timer, jiffies + 1);
>   }
>
> @@ -199,6 +201,7 @@ void led_stop_software_blink(struct led_classdev
> *led_cdev)
>       del_timer_sync(&led_cdev->blink_timer);
>       led_cdev->blink_delay_on = 0;
>       led_cdev->blink_delay_off = 0;
> +    led_cdev->flags &= ~LED_BLINKING_SW;
>   }
>   EXPORT_SYMBOL_GPL(led_stop_software_blink);
>
> @@ -209,7 +212,7 @@ void led_set_brightness(struct led_classdev *led_cdev,
>        * In case blinking is on delay brightness setting
>        * until the next timer tick.
>        */
> -    if (led_cdev->blink_delay_on || led_cdev->blink_delay_off) {
> +    if (led_cdev->flags & LED_BLINKING_SW) {
>           /*
>            * If we need to disable soft blinking delegate this to the
>            * work queue task to avoid problems in case we are called
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index bc1476f..08ef6f4 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -48,6 +48,7 @@ struct led_classdev {
>   #define LED_BLINK_DISABLE    (1 << 21)
>   #define LED_SYSFS_DISABLE    (1 << 22)
>   #define LED_DEV_CAP_FLASH    (1 << 23)
> +#define LED_BLINKING_SW     (1 << 24)
>
>       /* Set LED brightness level */
>       /* Must not sleep, use a workqueue if needed */

The above line looks different in the recent code.
Jacek Anaszewski May 16, 2016, 2:32 p.m. UTC | #11
On 05/16/2016 04:23 PM, Jacek Anaszewski wrote:
> On 05/16/2016 03:43 PM, Tony Makkiel wrote:
if (led_cdev->flags & LED_BLINK_SW) .
>>>
>>> LED_BLINK_SW flag would have to be cleared in led_stop_software_blink()
>>> and in the first two conditions in the led_timer_function().
>>>
>>
>> Yes, that will do with minimal changes. I tested the following, and
>> works.
>
> Fine, so could you please submit the patch officially?
> Before that, please rebase your code on top of LED tree or linux-next
> and change LED_BLINKING_SW to LED_BLINK_SW, to keep the same prefix for
> each blinking related definition.

Also please put it before LED_BLINK_ONESHOT.

Patch
diff mbox series

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