From mboxrd@z Thu Jan 1 00:00:00 1970 From: zhaoxiu.zeng@gmail.com (Zeng Zhaoxiu) Date: Fri, 8 Apr 2016 09:51:04 +0800 Subject: [PATCH] mtd: nand: s3c2410: fix bug in s3c2410_nand_correct_data() In-Reply-To: <20160408021817.274d4e59@bbrezillon> References: <1460047697-72830-1-git-send-email-zengzhaoxiu@163.com> <20160408021817.274d4e59@bbrezillon> Message-ID: <57070E88.5020008@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org ? 2016?04?08? 08:18, Boris Brezillon ??: > Hi Zeng, > > On Fri, 8 Apr 2016 00:48:17 +0800 > zengzhaoxiu at 163.com wrote: > >> From: Zeng Zhaoxiu >> >> If there is only one bit difference in the ECC, the function should return 1. >> The result of "diff0 & ~(1<> actually returns -1. >> >> Here, we can use the simple expression "(diff0 & (diff0 - 1)) == 0" to determine >> whether the diff0 has only one 1-bit. > Missing Signed-off-by here. > >> --- >> drivers/mtd/nand/s3c2410.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/mtd/nand/s3c2410.c b/drivers/mtd/nand/s3c2410.c >> index 9c9397b..c9698cf 100644 >> --- a/drivers/mtd/nand/s3c2410.c >> +++ b/drivers/mtd/nand/s3c2410.c >> @@ -542,7 +542,7 @@ static int s3c2410_nand_correct_data(struct mtd_info *mtd, u_char *dat, >> diff0 |= (diff1 << 8); >> diff0 |= (diff2 << 16); >> >> - if ((diff0 & ~(1<> + if ((diff0 & (diff0 - 1)) == 0) > Or just > > if (hweight_long((unsigned long)diff0) == 1) > > which is doing exactly what the comment says. > > BTW, I don't understand why the current code is wrong? To me, it seems > it's correctly detecting the case where only a single bit is different. > What are you trying to fix exactly? > > Best Regards, > > Boris > For example, assuming diff0 is 1, then fls(diff0) is equal to 1, then "~(1 << fls(diff0))" is equal to 0xfffffffd, then the result of "(diff0 & ~(1 << fls(diff0)))" is 1 , not we expected 0. __fls(diff0) and "(fls(diff0) - 1)" are all right, but fls(diff0) is wrong.