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    SubjectRe: [PATCH v4 2/7] dt-bindings: ti-lmu: Modify dt bindings for the LM3697
    On Thu, Oct 25, 2018 at 08:27:18PM +0200, 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.

    Yes. I'd also add it should be along the lines of for a given
    board it's always configured in that way or is it something you'd want
    in the BIOS of your PC.

    Rob

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