linux-kernel - Re: [PATCH 04/10] omap_hwspinlock: Replace "hweight_long(i & 0xf) != 1" with "!is_power_of

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Message-ID: <56659FC2.1070906@gmail.com>
Date:	Mon, 7 Dec 2015 23:03:30 +0800
From:	"zhaoxiu.zeng" <zhaoxiu.zeng@...il.com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] omap_hwspinlock: Replace "hweight_long(i & 0xf) !=
 1" with "!is_power_of_2(i & 0xf)"

在 2015/12/7 19:08, Ohad Ben-Cohen 写道:
> Hi,
> 
> On Sun, Dec 6, 2015 at 12:33 PM, Zhaoxiu Zeng <zhaoxiu.zeng@...il.com> wrote:
>>
>> From: Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>
>>
>> Signed-off-by: Zeng Zhaoxiu <zhaoxiu.zeng@...il.com>
> 
> Please explain why do you think we should make this change.

is_power_of_2 is simple, and faster than "hweightN(x) == 1" on most architectures.
And the "& 0xf" operation is unnecessary, we will check whether or not greater than 8 behind.

> 
> Btw, the original code used is_power_of_2, but we thought hweight is
> more explicit so it was adopted.
> 
> Thanks,
> Ohad.
> 

---
 drivers/hwspinlock/omap_hwspinlock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwspinlock/omap_hwspinlock.c b/drivers/hwspinlock/omap_hwspinlock.c
index ad2f8ca..1848a4c 100644
--- a/drivers/hwspinlock/omap_hwspinlock.c
+++ b/drivers/hwspinlock/omap_hwspinlock.c
@@ -29,6 +29,7 @@
 #include <linux/hwspinlock.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/log2.h>
 
 #include "hwspinlock_internal.h"
 
@@ -125,7 +126,7 @@ static int omap_hwspinlock_probe(struct platform_device *pdev)
 		goto iounmap_base;
 
 	/* one of the four lsb's must be set, and nothing else */
-	if (hweight_long(i & 0xf) != 1 || i > 8) {
+	if (!is_power_of_2(i) || i > 8) {
 		ret = -EINVAL;
 		goto iounmap_base;
 	}
-- 

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