linux-kernel - Re: [RFC PATCH 1/2] sbs-battery: add forced instantiation from device tree

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Date:	Wed, 24 Sep 2014 20:59:34 +0200
From:	Frans Klaver <fransklaver@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	olof@...om.net, anton.vorontsov@...aro.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] sbs-battery: add forced instantiation from
 device tree

On Wed, Sep 24, 2014 at 04:34:32PM +0100, Mark Rutland wrote:
> On Wed, Sep 24, 2014 at 04:14:48PM +0100, Frans Klaver wrote:
> > On Wed, Sep 24, 2014 at 03:38:49PM +0100, Mark Rutland wrote:
> > > On Wed, Sep 24, 2014 at 03:22:22PM +0100, Frans Klaver wrote:
> > > You mention that there's a GPIO that can be used to detect the battery
> > > presence. Why can't the driver always probe and then on check for the
> > > presence of the battery dynamically using that GPIO? That should cover
> > > both cases.
> > 
> > I would say that this was the case before [1] was done. The GPIO is
> > optional and if not configured, the presence or absence of the battery
> > is detected by checking a status register much like probe() currently
> > does. It seems all cases were covered before that patch. If you worry
> > about speed, you should use the GPIO. I wonder if we might be able to
> > revert [1] without doing much harm.
> 
> But reverting that would re-introduce the lag on some systems, no? Given
> the wording of the original commit I would guess that the GPIO wasn't
> available. Perhaps Olof or Anton can enlighten us?

It probably would yes. The battery_detect gpio was last touched in 2011, the
probe check was added somewhere in 2012.

We could keep it as a compile option.

> In the cases where a GPIO is available, I think we should be able to be
> less pessimistic. Is a GPIO available in your case?

We don't have the battery_detect pin available. Incidentally, a bit of
lag reading out the battery is not a problem for us.

> Mark.
> 
> > 
> > Thanks,
> > Frans
> > 
> > [1] a22b41a31e53 "sbs-battery: Probe should try talking to the device"
> > 
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