linux-kernel - Re: [PATCH] include/log2.h: Fix rounddown_pow_of

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Date:	Wed, 23 Nov 2011 00:34:28 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Andrei Warkentin <andreiw@...are.com>,
	linux-kernel@...r.kernel.org,
	Rolf Eike Beer <eike-kernel@...tec.de>,
	opensuse-kernel@...nsuse.org,
	Sergiu Iordache <sergiu@...omium.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	Eddie Wai <eddie.wai@...adcom.com>,
	Jayamohan Kallickal <jayamohan.kallickal@...lex.com>
Subject: Re: [PATCH] include/log2.h: Fix rounddown_pow_of_two(1)

On Thu, 17 Nov 2011, Andrew Morton wrote:

[snip]

> drivers/mmc/host/sh_mmcif.c unnecessarily uses __rounddown_pow_of_two()
> then feeds the result into ilog2() in an apparent attempt to
> reimplement fls().

Yeah, I was wondering too, but wasn't sufficiently motivated to patch 
it;-) I'll test this "obvious" patch tomorrow and submit then:

diff --git a/drivers/mmc/host/sh_mmcif.c b/drivers/mmc/host/sh_mmcif.c
index c021482..824fee5 100644
--- a/drivers/mmc/host/sh_mmcif.c
+++ b/drivers/mmc/host/sh_mmcif.c
@@ -16,6 +16,7 @@
  *
  */
 
+#include <linux/bitops.h>
 #include <linux/clk.h>
 #include <linux/completion.h>
 #include <linux/delay.h>
@@ -386,7 +387,7 @@ static void sh_mmcif_clock_control(struct sh_mmcif_host *host, unsigned int clk)
 		sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_SUP_PCLK);
 	else
 		sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_CLEAR &
-			(ilog2(__rounddown_pow_of_two(host->clk / clk)) << 16));
+				((fls(host->clk / clk) - 1) << 16));
 
 	sh_mmcif_bitset(host, MMCIF_CE_CLK_CTRL, CLK_ENABLE);
 }

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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