linux-kernel - Re: [PATCH v2 3/4] leds: add LM3533 LED driver

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Message-ID: <20120503164641.GE15752@localhost>
Date:	Thu, 3 May 2012 18:46:41 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Rob Landley <rob@...dley.net>, Richard Purdie <rpurdie@...ys.net>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Jonathan Cameron <jic23@....ac.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2 3/4] leds: add LM3533 LED driver

On Thu, May 03, 2012 at 03:51:08PM +0100, Mark Brown wrote:
> On Thu, May 03, 2012 at 01:50:59PM +0200, Johan Hovold wrote:
> > On Thu, May 03, 2012 at 11:43:44AM +0100, Mark Brown wrote:
> 
> > > > +		5 - 4.194 s
> > > > +		6 - 8.389 s
> > > > +		7 - 16.78 s
> 
> > > Shouldn't these be controlled by led_blink_set() rather than a custom
> > > ABI?
> 
> > led_blink_set controls the on/off times, but the LM3533 has the two
> > additional rise and fall-time settings which determine the transition
> > time between these states.
> 
> Hrm.  In that case these rise times are very large - I'd expect them to
> cause issues with led_set_blink() users?

They are. The default settings (as fast a transition as possible) will
probably what most people use, and if they start fiddling with the
transition times they probably know what they're doing.

> Though actually I suspect the
> solution here is to pull these out into the framework later; we can
> probably simulate reasonably in software with a lot of brightness
> variable LEDs.

Ok.

> > > > +What:		/sys/class/leds/<led>/max_current
> 
> > > Shouldn't this be set by platform data, the maximum current you can push
> > > through the LEDs seems like a board dependant thing which won't change
> > > dynamically at runtime.  The brightness can already be varied.
> 
> > I fully agree and it is possible to set via the platform data for that
> > reason. The end-customer, however, insisted that even this setting be
> > available through sysfs to facilitate their integration and testing.
> 
> > I'd be willing drop this attribute if requested, as it would only be used
> > during integration and could easily be added back by the end-customer if
> > needed.
> 
> I'd strongly suggest removing this for mainline.  If it's present it
> should at least be limited to the maximum specified in platform data
> (just for safety if nothing else).

Agreed.

Thanks,
Johan
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