linux-kernel - Re: [PATCH/RFC v10 08/19] leds: Add support for max77693 mfd flash cell

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Date:	Mon, 12 Jan 2015 14:25:21 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
Cc:	linux-leds@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	kyungmin.park@...sung.com, b.zolnierkie@...sung.com,
	cooloney@...il.com, rpurdie@...ys.net, sakari.ailus@....fi,
	s.nawrocki@...sung.com, Andrzej Hajda <a.hajda@...sung.com>,
	Lee Jones <lee.jones@...aro.org>,
	Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH/RFC v10 08/19] leds: Add support for max77693 mfd flash
 cell

Hi!

> >>+struct max77693_sub_led {
> >>+	/* related FLED output identifier */
> >
> >->flash LED, about 4x.
> >
> >>+/* split composite current @i into two @iout according to @imax weights */
> >>+static void __max77693_calc_iout(u32 iout[2], u32 i, u32 imax[2])
> >>+{
> >>+	u64 t = i;
> >>+
> >>+	t *= imax[1];
> >>+	do_div(t, imax[0] + imax[1]);
> >>+
> >>+	iout[1] = (u32)t / FLASH_IOUT_STEP * FLASH_IOUT_STEP;
> >>+	iout[0] = i - iout[1];
> >>+}
> >
> >Is 64-bit arithmetics neccessary here? Could we do the FLASH_IOUT_STEP
> >divisons before t *=, so that 64-bit division is not neccessary?
> 
> It is required. All these operations allow for splitting the composite
> current into both outputs according to weights given in the imax
>array.

I know.

What about this?

static void __max77693_calc_iout(u32 iout[2], u32 i, u32 imax[2])
{
	u32 t = i;

	t *= imax[1] / FLASH_IOUT_STEP;
	t = t / (imax[0] + imax[1]);
	t /= FLASH_IOUT_STEP

	iout[1] = (u32)t;
	iout[0] = i - iout[1];
}

Does it lack precision?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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