linux-kernel - Re: [PATCH] rtc: ds1307: add trickle charger device tree binding

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Message-ID: <20140908145825.GO12081@leverpostej>
Date:	Mon, 8 Sep 2014 15:58:25 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Pavel Machek <pavel@...x.de>
Cc:	Matti Vaittinen <matti.vaittinen@....com>,
	ext Guenter Roeck <linux@...ck-us.net>,
	Jason Cooper <jason@...edaemon.net>,
	"a.zummo@...ertech.it" <a.zummo@...ertech.it>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"arno@...isbad.org" <arno@...isbad.org>,
	"jgunthorpe@...idianresearch.com" <jgunthorpe@...idianresearch.com>,
	"san@...etechnology.dk" <san@...etechnology.dk>,
	"hs@...x.de" <hs@...x.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Sverdlin Alexander <alexander.sverdlin@....com>
Subject: Re: [PATCH] rtc: ds1307: add trickle charger device tree binding

On Mon, Sep 08, 2014 at 02:52:42PM +0100, Pavel Machek wrote:
> Hi!
> 
> > I would suggest we have two properties that describe the resistor's
> > rating and whether or not there is a diode:
> > 
> > trickle-resistor-ohms = <250>
> > diode-connected;
> > 
> > That's easy for a human to write and/or validate, we can easily extend
> > it in future, requires no proliferation of macros, and describes the
> > hardware rather than telling software what to do.
> > 
> > The driver becomes a little more complicated, but gains sanity checking,
> > which is a good thing.
> 
> Certainly looks better than register bit defines.
> 
> As rtc-bq32k has similar options, I'm interested, too. I believe we
> should add
> 
> trickle-charge-enable;
> 
> (we may not want to charge at all), and I believe the diode should be
> 
> disconnect-diode;
> 
> ... With diode connected, charge is slower, and that probably should
> be the default value. We don't want to give too much current in
> default case.  (bq32k has hard-coded resistor value for
> diode/not-diode case).

I agree that if one case is less likely to be problematic / damaging
that should be the default.

Mark.
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