Re: [PATCH v4 2/7] dt-bindings: ti-lmu: Modify dt bindings for the LM3697

[Dan Murphy <dmurphy@ti.com>]

Jacek

On 10/25/2018 01:27 PM, Jacek Anaszewski wrote:
> On 10/25/2018 08:07 PM, Dan Murphy wrote:
>> Rob
>>
>> On 10/24/2018 09:54 AM, Rob Herring wrote:
>>> On Wed, Oct 24, 2018 at 07:07:57AM -0500, Dan Murphy wrote:
>>>> Pavel
>>>>
>>>> On 10/24/2018 04:04 AM, Pavel Machek wrote:
>>>>> Hi!
>>>>>
>>>>>> The LM3697 is a single function LED driver. The single function LED
>>>>>> driver needs to reside in the LED directory as a dedicated LED driver
>>>>>> and not as a MFD device.  The device does have common brightness and ramp
>>>>>
>>>>> So it is single function LED driver. That does not mean it can not
>>>>> share bindings with the rest. Where the bindings live is not imporant.
>>>>>
>>>>
>>>> It can share bindings that are correctly done, not ones that are incomplete and incorrect.
>>>>
>>>> Where bindings live is important to new Linux kernel developers and product 
>>>> developers looking for the proper documentation on the H/W bindings.
>>>>
>>>>>> reside in the Documentation/devicetree/bindings/leds directory and follow the
>>>>>> current LED and general bindings guidelines.
>>>>>
>>>>> What you forgot to tell us in the changelog:
>>>>
>>>> I can add this to the changelog.
>>>>
>>>>>
>>>>>> +Optional child properties:
>>>>>> +	- runtime-ramp-up-msec: Current ramping from one brightness level to
>>>>>> +				the a higher brightness level.
>>>>>> +				Range from 2048 us - 117.44 s
>>>>>
>>>>> The other binding uses "ramp-up-msec". Tell us why you are changing this, or
>>>>> better don't change things needlessly.
>>>>>
>>>>> We don't want to be using "runtime-ramp-up-msec" for one device and
>>>>> "ramp-up-msec" for the other.
>>>>
>>>> This is another example of how the original bindings were incorrect and misleading.
>>>>
>>>> The LM3697 have 2 ramp implementations that can be used.
>>>>
>>>> Startup/Shutdown ramp and Runtime Ramp.  Same Ramp rates different registers and
>>>> different end user experience.
>>>>
>>>> So having a single node call ramp-up-msec is misleading and it does not
>>>> indicate what the H/W will do.
>>>
>>> The existing ones aren't documented (present in the example is not 
>>> documented). This seems like something that should be common rather than 
>>> TI specific. Though it also seems more like something the user would 
>>> want to control (i.e. sysfs) rather than fixed in DT.
>>>
>>
>> Changing the runtime ramping or startup/shutdown ramping could also be done via sysfs.
>> I am not dedicated to having it in the DT file I was following prior art.
>>
>> Jacek
>>
>> Do you have an opinion on this?
> 
> This is this problem with the Device Tree's scope of responsibility.
> It is defined as a means for "describing the hardware", but often
> this rule is abused by the properties that fall into "configuration"
> category. E.g. default-state, retain-state-suspended from leds-gpio.txt
> or linux-default-trigger from common LED bindings.
> 
> In some cases this is justified. The question is whether it is something
> that necessarily needs to be configured on driver probing? If not, then
> I'd go for sysfs interface.
> 

Appreciate the feedback.  I think you and Rob are right. This should be a sysfs
entry.  I can think of instances where the ramp times might want to be modified 
or even turned off.

I will change that implementation.

Dan

-- 
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Dan Murphy