linux-kernel - Re: [PATCH v14 2/2] leds: Add driver for Qualcomm LPG

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Date:   Fri, 6 May 2022 18:09:01 +0200
From:   Pavel Machek <pavel@....cz>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
        Lee Jones <lee.jones@...aro.org>, Luca Weiss <luca@...tu.xyz>,
        Doug Anderson <dianders@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v14 2/2] leds: Add driver for Qualcomm LPG

Hi!

> > > +    "255 500 0 500"
> > > +
> > > +        ^
> > > +        |
> > > +    255 +----+    +----+
> > > +        |    |    |    |      ...
> > > +      0 |    +----+    +----
> > > +        +---------------------->
> > > +        0    5   10   15     time (100ms)
> > > +
> > > +The LPG supports specifying a longer hold-time for the first and last element
> > > +in the pattern, the so called "low pause" and "high pause".
> > 
> > Please see
> > Documentation/devicetree/bindings/leds/leds-trigger-pattern.txt . This
> > should really be compatible.
> 
> Unfortunately the LPG hardware only supports fixed duration (except for
> the ability to hold/extend the first and last duration in the pattern)
> and it also does not support gradual transition between the brightness
> levels.

Ok.

> As such the pattern sequence provided to hw_pattern looks to be the
> smae, but I don't see that it can be made compatible.
> 
> > Can I get either patch to disable pattern infrastructure for now or to
> > get it compatible?
> > 
> 
> I'd be happy to get this updated to your liking, but this was one of the
> drivers we discussed when we introduced the pattern trigger and led to
> the conclusion that we need the ability to do hw-specific patterns.
> 
> As such this document provides the hardware specific documentation, as
> we describe under "hw_pattern" in
> Documentation/ABI/testing/sysfs-class-led-trigger-pattern.
> 
> Please advice on what you would like me to do.

I'd like you to use same format leds-trigger-pattern describes.

If someone passes "255 500 0 500", that's requesting gradual transitions and
your hw can not do that. You return -EINVAL.

If someone wants that kind of blinking, they need to pass "255 0 255 500 0 0 0 500".

Best regards,
									Pavel


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