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

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Date:   Wed, 24 Oct 2018 09:54:34 -0500
From:   Rob Herring <robh@...nel.org>
To:     Dan Murphy <dmurphy@...com>
Cc:     Pavel Machek <pavel@....cz>, jacek.anaszewski@...il.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org, lee.jones@...aro.org, tony@...mide.com
Subject: Re: [PATCH v4 2/7] dt-bindings: ti-lmu: Modify dt bindings for the
 LM3697

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.

Rob