linux-kernel - Re: Generic battery interface

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Date:	Sat, 29 Jul 2006 12:48:51 +0300
From:	"Shem Multinymous" <multinymous@...il.com>
To:	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>
Cc:	"Vojtech Pavlik" <vojtech@...e.cz>, "Pavel Machek" <pavel@...e.cz>,
	"Brown, Len" <len.brown@...el.com>,
	"Matthew Garrett" <mjg59@...f.ucam.org>,
	"kernel list" <linux-kernel@...r.kernel.org>,
	linux-thinkpad@...ux-thinkpad.org, linux-acpi@...r.kernel.org
Subject: Re: Generic battery interface

On 7/29/06, Valdis.Kletnieks@...edu <Valdis.Kletnieks@...edu> wrote:
> On Sat, 29 Jul 2006 01:10:40 +0300, Shem Multinymous said:
> > On 7/28/06, Valdis.Kletnieks@...edu <Valdis.Kletnieks@...edu> wrote:
> > > Is there a reliable (or hack-worthy) way for the kernel to determine how
> > > often the values are re-posted by the hardware?
> >
> > That's hardware-specific. Some drivers can know, others may just
> > assume 1sec or 0.1sec or whatever.
>
> That smells suspiciously like "We need an API for the hardware-specific
> bits f code to pass the generic bits a value for this..." (and the
> hardware-specific part can either ask the battery, or return a
> hard-coded "10 seconds" that somebody measured, or whatever)....

I don't think "update frequency" is a good abstraction. The hardware's
update may not be variable and irrregular (e.g., event-based), and
there's there's an issue of phase sync to avoid unnecessary latency.

The lazy polling approach I described in my last post to Vojtech
("block until there's  a new readout or N milliseconds have passed,
whichever is later") looks like a more general, accurate and efficient
interface.

  Shem
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