On 04/16/2015 02:21 PM, Jacek Anaszewski wrote:
> Hi Vasant,
>
> On 04/16/2015 08:52 AM, Vasant Hegde wrote:
>> On 04/15/2015 06:42 PM, Jacek Anaszewski wrote:
>>> On 04/15/2015 12:15 PM, Vasant Hegde wrote:
>>>> On 04/15/2015 02:12 PM, Jacek Anaszewski wrote:
>>>>> Hi Vasant,
>>
>> Hi Jacek,
>>
>> .../...
>>
>>>>>>>
>>>>>>
>>>>>> I mean, we have to retain the state of LED across system reboot.
>>>>>
>>>>> Static variables are reinitialized on system reboot, aren't they?
>>>>
>>>> Sorry. I think comment was confusing..
>>>>
>>>> As I understood, classdev_unregister call resets all LEDs state. However in our
>>>> case, we don't
>>>> want to change the LED state during system shutdown/reboot.
>>>>
>>>> Hence I have introduced state variable here. So during register call, I just
>>>> disable LEDs so that any further call will just return. That way we retain LED
>>>> state even after unloading module.
>>>>
>>>> Please let me know if there is any better way to achieve this.
>>>
>>> Since this is not a feature of the device, but rather a use case, then
>>> it cannot be hard coded in the driver this way. The solution I see is
>>> introducing a sysfs attribute that would determine if we want the
>>> LED to be turned off on unregistration or not.
>>
>> Hmmm. I thought having simple various is enough ..
>>
>> I don't know the usage of other LED drivers .. Just a thought .. How about
>> enabling this feature in LED class itself ...Something like:
>> - Add new attribute to generic LED class (say persistent)?
>> - If drivers wants to retain LED state across reboot, then enable this option
>> - During unregister call check for this attribute
>>
>>>
>>> You can refer to the following driver to find out how to add the
>>> sysfs attribute:
>>>
>>> drivers/leds/leds-lm3533.c
>>>
>>> The attribute will also have to be documented, similarly to these:
>>>
>>> Documentation/ABI/testing/sysfs-class-led-driver-lm3533
>>>
>>> Currently I don't have a good candidate for attribute
>>> name, so feel free to propose one.
>>
>> If you don't like generic attribute, then shall I introduce "persistent"
>> attribute inside my driver. ?
>> - By default this attribute is ON and if user wants he can disable this .
>> - And I will have another variable (say op_support).. which I will disable in
>> unload path..
>> .../...
>>
>>>>>
>>>>> 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" ?
>>>
>>> Sounds good.
>>>
>>>> - 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.
>>>
>>> Does it mean that the LED can be controlled from hardware?
>>> If so, what would be software use cases then? The same question is
>>> related to the attn and indent states.
>>
>> - Identify LEDs:
>> We have service processor interface to set/reset this LEDs.. Similar operation
>> can be done from inband interface as well (via user space tools in Linux)..
>> Later management layer can make use of this.
>>
>> - Fault / Attention :
>> FW can SET these LEDs if its capable of isolating problem.
>> Similarly host/user space can SET these LEDs if then can do fine grained
>> problem isolation etc.
>> Host/user space can RESET these LEDs.
>>
>> Hence we are adding host support to all the LEDs which can be modified by host.
>>
>> Hope this clarifies.
>
> Thanks for this explanation.
>
> I am changing my mind about these LEDs. Since they can be controlled
> from hardware without any system interaction, then turning them off
> on driver removal makes no sense. The LEDs could be turned on again even
> if the driver is unloaded.
> Since the driver doesn't perform any initialization of the LEDs,
> neither should it turn them off on removal.
>
> If I understand this correctly, then the solution with variable would
> do and no sysfs attribute would be required.
>
Jacek,
Thanks. Then I will retain current method.
One question..What is the preferred way to name LED node in this case ?
<location_code>:<ATTENTION|IDENTIFY|FAULT>
OR
<location_code>
ident <- attribute under each node
fault
attention
-Vasant
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