[PATCH v2 2/2] leds/powernv: Add driver for PowerNV platform

Jacek Anaszewski j.anaszewski81 at gmail.com
Thu Apr 23 07:45:09 AEST 2015

Hi Vasant,

On 20.04.2015 17:53, Vasant Hegde wrote:
> On 04/20/2015 08:50 PM, Jacek Anaszewski wrote:
>> On 04/20/2015 02:34 PM, Vasant Hegde wrote:
>>> On 04/20/2015 05:15 PM, Jacek Anaszewski wrote:
>>>> Hi Vasant,
>>>> I'd like to clarify some details regarding your explanation.
>>>> On 04/15/2015 12:15 PM, Vasant Hegde wrote:
>>>> [...]
>>>>>>> In Power Systems LEDs are overloaded (meaning same LED is used
>>>>>>> for identify and
>>>>>>> fault depending on their state  ---  blinking = identify and
>>>>>>> solid = fault). Hence here append LED type info.
>>>>>> The label could be composed of segments and an ordinal number as
>>>>>> labels have to be unique, e.g. attn_ident_0, attn_ident_1.
>>>>>> The segments would have to be parsed by the driver to discover
>>>>>> all the LED's available modes.
>>>>>> nitpicking: identify is a verb and is not a proper name for the
>>>>>> LED. Could you describe the purpose of this mode, so that we
>>>>>> could come up with a better name?
>>>>> Each component (Field Replacement Unit) will have service
>>>>> indicator (LEDS) which
>>>>> can have below states :
>>>>>      - OFF     : no action
>>>>>      - Identify: blinking state (user can use this state to
>>>>> identify particular component).
>>>>>           In Power Systems world we call it as "identify"
>>>>> indicator.. Hence I retained same name here.
>>>>>           How about just "ident" ?
>>>>>      - fault : solid state (when component goes bad, LED goes to
>>>>> solid state) Note that our FW is capable of isolating some of the
>>>>> issues and it can turn
>>>>> on LEDs without OS
>>>>>          interference.
>>>>> We have one more System level LED (System Attention Indicator)..
>>>>> This LED has two states:
>>>>>      - OFF : Everything is fine
>>>>>      - ON : Some component has issues and needs attention.
>>>> We have three modes:
>>>> - identify        - blinking
>>>> - fault            - solid
>>>> - attention indicator    - solid
>>>> How does LED operation differ for fault and attention modes?
>>>> Does a LED have different intensity?
>>> Jacek,
>>> System Attention LED is special LED and its single LED
>>> available/system. where as identify and fault is applicable to all
>>> field replaceable units in the system..
>>> So Typical server will have
>>>      1   System Attention LED
>>>       N  Identify/fault LED (N = Field Replaceable Unit).
>>> Apart from above two, we do have two more LEDs/Enclosure (external
>>> visible LEDs)
>>>     - Enclosure Identify
>>>     - Enclosure fault
>>>         These LEDs reflects state of all Field Replaceable Units
>>> (FRU) inside this enclosure
>>>          If any of FRU state is ON, this will become ON
>>>          Also we can independently enable this LED!!
>>>       But from kernel side implementation point of view, I just
>>> treat this as another LED.. as our platform code (OPAL firmware)
>>> takes care of roll up etc.
>>> Now our LED can operate in two mode (Depending on our service
>>> model, typically one/two socket servers are Light Path mode,
>>> whereas high end servers are Guiding Light Mode).
>>>    1.  Guiding Light
>>>        Only Identify indicator is support.. Fault is not supported
>>>        System attention indicator is used to point there is some
>>> problem in system and need attention
>>>     2. Light Path mode
>>>       Both identify and fault indicator is supported ..
>>>       Fault is ON whenever some component is faulty
>>>       System attention indicator is used to point that FW/OS is not
>>> able to isolate the problem and needs user to look into serviceable
>>> event (like syslog/ our agents like ESA which analyzes and reports
>>> events)
>>> Handling LED states :
>>>     - Though physically single LED is overloaded for identify and
>>> fault, logically (FW/OS level) we treat them as separate LED.
>>>     - We can enable both fault and identify simultaneously.
>>>     - Hardware decides physical LED state (rule : identify has
>>> priority over fault).
>>>        ex: Say location code 'X',
>>>              Identify = ON, fault = ON ,   state of 'X' = identify
>>> (blinking) Identify = OFF, fault = ON,   state of 'X'  = fault
>>> (solid) Identify = OFF, fault = ON,   state of 'X'  = identify
>>> (blinking) Identify = OFF, fault = OFF , state of 'X'  = OFF
>>> Since we have various above combinations, I thought its best to
>>> have separate class dev for each individual LEDs. That way we keep
>>> everything simple and let firmware handle all complexities.
>>> Hope this clarifies.
>>> I just posted v3 where I addressed your comments.
>>>      https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-April/127702.html
>>> Please let me know if you have any comments/suggestions.
> Jacek,
>>  From what I can see from the driver code the LEDs are set with:
>> opal_leds_set_ind(token, loc_code, led_mask, led_value,
>> &max_led_type);
>> and their state can be read with:
>> opal_leds_get_ind(loc_code, &led_mask, &led_value, &max_led_type)
>>  From the kernel point of view these are very simple operations.
>> All the logic you described should be handled by user space.
>> If you need to be able to specify the LED mode you want to set/read,
>> then additional 'mode' sysfs attribute should be added by the driver.
>> There would have to be also additional sysfs attribute
>> 'available_modes" provided. The ABI documentation should inform how
>> the mode identifiers map to the modes. I already explained how to
>> add it, when we were discussing about retaining led state on remove.
> Sorry..My fault.. I should have elaborated mode operation...

What I was thinking about here was actually LED type, not mode in terms
of Guiding Light/Light Path. However, please look at the newest
approach in the end of this message.

> I forgot to mention that LED mode is static... meaning platform
> provides this information, but we cannot change during runtime..
> Presently we have this information in Device Tree. Since this is
> static one (and also LED Mode is system wide.. nothing to do
> individual LED),  I didn't add it in LED driver code.. .Do you think
> we should add that property ?

The property shouldn't be documented at all if it isn't to be used.

>> I'd see following use cases.
>> (let's assume that modes are defined as follows:
>> 0: ident, 1: attn, 2: fault)
> Modes are : Guiding Light / Light Path ... which is static and
> platform provides this information.
> LED types : IDENT, FAULT and ATTN .... which can be get/set/reset by
> OS (kernel/userspace)
> Also only 1 LED can be ATTN ...
>> #cat available_modes
>> #0 1 2
>> #echo 0 > mode  //set ident mode
>> #echo 1 > brightness //set ident state
>> #echo 2 > mode  //set fault mode
>> #cat brightness //read fault state
>> #0
>> #echo 1 > attn //set attn mode
>> #echo 1 > brightness
>> This would set the LED in blinking mode, so I am wondering if we
>> shouldn't employ timer trigger for this to keep the LED API
>> consistent.
>> Can a single LED support other mode than 'attention'? I'd like to
>> know if a LED in attention mode (blinking), can be set to some solid
>> mode?
> No.. Its always single attention LED/system ... which can be Set
> (Solid) / reset state.

I confused it with ident.

>> Please let me know if such an approach would still not fit for your
>> requirements.
> Given above conditions, I think current approach (my v3 patchset) is
> simple and works better. What you say?

Yes, but we still have naming and blinking issues to solve.

Please look at this draft design of device tree node:

opal-leds {
        compatible = "ibm,opal-v3-led";

        U78C9.001.RST0027-P1-C1:attn {


        U78C9.001.RST0027-P3-C2:identify:fault {

The LED nodes could be empty as the name would convey all the
required information. The implications would be as follows:

1. Each LED would have one corresponding LED class device.

2. Operations on attn and fault LED types:
	turn on:
		echo 255 > brightness
	turn off:
		echo 0 > brightness
	get status
		cat brightness
3. Operations on identify LED:
	turn on:
		echo "timer" > trigger
		(blink_set op would have to be implemented in the
	turn off:
		echo 0 > brightness
	get status:
		support for this would have to be added to the LED
		subsystem core

4. Since 'identify' is the platform specific name it could be preserved

Does it work for you?

Best Regards,
Jacek Anaszewski

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