linux-kernel - Re: [PATCH v8 5/8] Loongson: YeeLoong: add hardware monitoring driver

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Date:	Mon, 07 Dec 2009 08:54:58 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Ralf Baechle <ralf@...ux-mips.org>, akpm@...ux-foundation.org,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Rafael J . Wysocki" <rjw@...k.pl>, zhangfx@...ote.com,
	linux-laptop@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v8 5/8] Loongson: YeeLoong: add hardware monitoring
 driver

On Sun, 2009-12-06 at 09:47 +0100, Pavel Machek wrote: 
> Hi!
> 
> > +static int get_battery_current(void)
> > +{
> > +	s16 value;
> > +
> > +	value = (ec_read(REG_BAT_CURRENT_HIGH) << 8) |
> > +		(ec_read(REG_BAT_CURRENT_LOW));
> > +
> > +	if (value < 0)
> > +		value = ~value + 1;
> > +
> > +	return value;
> > +}
> 
> What is going on here? I thought the value is already in two's
> complement... Is the above equivalent of
> 
> 	      if (value < 0)
> 	      	 value = -value; 
> 
> ? If so, why? If not, can you add a comment?

Right, then, will use this instead:

static int get_battery_current(void)
{ 
	s16 value;

	value = (ec_read(REG_BAT_CURRENT_HIGH) << 8) |
		(ec_read(REG_BAT_CURRENT_LOW));

	return abs(value);
}

Thanks & Best Regards,
	Wu Zhangjin


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