linux-kernel - Re: HTC Dream aka. t-mobile g1 support

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Message-ID: <a55d774e0906121527n16019225q81084945a38bb97e@mail.gmail.com>
Date:	Fri, 12 Jun 2009 15:27:01 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Ian Molton <ian@...menth.co.uk>
Cc:	Pavel Machek <pavel@....cz>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	san@...roid.com, rlove@...gle.com, Greg KH <greg@...ah.com>
Subject: Re: HTC Dream aka. t-mobile g1 support

On Fri, Jun 12, 2009 at 3:02 PM, Ian Molton<ian@...menth.co.uk> wrote:
> Brian Swetland wrote:
>
>> Yup.  It's an HTC specific thing -- some of their devices don't have a
>> battery gauge IC and estimate current drain based on hints provided to
>> the baseband from the apps processor.  I'm not particularly thrilled
>> with the interface, but without it the battery level estimation is
>> flakier.
>
> Is there a reason that this couldnt be done in userspace?

It'd be a lot more overhead -- in some cases it's updated with
relatively fine granularity (wifi driver changing state, backlight
changing, etc), and on the kernel side it's just updating a shared
memory location with the current estimate.  Userspace doesn't
necessarily have the visibility into driver state to update it
accurately, and punching that information down to userspace and then
having userspace feed it back up to the kernel seems like more
overhead and code to maintain to me.

Brian
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