Thread (91 messages) 91 messages, 8 authors, 2015-02-09

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

From: Pavel Machek <hidden>
Date: 2015-01-12 13:25:28
Also in: linux-leds, linux-media, lkml

Hi!
quoted
quoted
+struct max77693_sub_led {
+	/* related FLED output identifier */
->flash LED, about 4x.
quoted
+/* 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
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help