From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [patch 09/11] b44: fix eeprom endianess issue Date: Tue, 26 Sep 2006 11:59:28 -0400 Message-ID: <45194E60.4010701@garzik.org> References: <200609252339.k8PNdNE4002654@shell0.pdx.osdl.net> <45186D66.1000508@garzik.org> <200609261747.25575.mb@bu3sch.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Gary Zambrano , akpm@osdl.org Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:8325 "EHLO mail.dvmed.net") by vger.kernel.org with ESMTP id S932158AbWIZP7b (ORCPT ); Tue, 26 Sep 2006 11:59:31 -0400 To: Michael Buesch In-Reply-To: <200609261747.25575.mb@bu3sch.de> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Michael Buesch wrote: > On Tuesday 26 September 2006 01:59, Jeff Garzik wrote: >> akpm@osdl.org wrote: >>> From: Michael Buesch >>> >>> This fixes eeprom read on big-endian architectures. >>> >>> Signed-off-by: Michael Buesch >>> Cc: Jeff Garzik >>> Signed-off-by: Andrew Morton >>> --- >>> >>> drivers/net/b44.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff -puN drivers/net/b44.c~b44-fix-eeprom-endianess-issue drivers/net/b44.c >>> --- a/drivers/net/b44.c~b44-fix-eeprom-endianess-issue >>> +++ a/drivers/net/b44.c >>> @@ -2055,7 +2055,7 @@ static int b44_read_eeprom(struct b44 *b >>> u16 *ptr = (u16 *) data; >>> >>> for (i = 0; i < 128; i += 2) >>> - ptr[i / 2] = readw(bp->regs + 4096 + i); >>> + ptr[i / 2] = cpu_to_le16(readw(bp->regs + 4096 + i)); >> Seems highly silly to me: readw() already swaps on big endian, so >> you're just swapping again. And then... read the call of >> b44_read_eeprom(): bp->dev->dev_addr[] assignment is such that it swaps >> YET AGAIN. >> >> Seems like a better solution would be to remove the manual swap from the >> caller of b44_read_eeprom(). > > I already explained this to you, but I will repeat me. > readw returns the data in CPU order. > With cpu_to_le16 we convert it to little endian, because > "ptr" is a pointer to a _byte_ arrray. See the cast above. > A byte array is little endian. > Should I go into deeper detail, or did you get it? ;) > > The dev_addr assignment _intentionally_ swaps yet again, because > the values are stored in bigendian format in the SPROM. > > Removing the swap for dev_addr would definately the worse and wrong > solution. AFAICS it's an obviously-correct end result, with far fewer swaps to boot. Jeff