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

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Message-ID: <20181026083037.GA19434@amd>
Date:   Fri, 26 Oct 2018 10:30:37 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Dan Murphy <dmurphy@...com>, Rob Herring <robh@...nel.org>,
        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

Hi!

> >>>>> +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

> 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.

I always assumed that ramp-up time is there because hardware (power
supply?) can not handle "too fast" switching. Missing capacitors or
something. If so, this needs to be in device tree.

If not, it indeed does not belong to device tree.

> 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.

While this would be useful for hardware accelerated patterns, I doubt
we want to make it configurable without that support.

									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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