Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754955AbbHKCGa (ORCPT ); Mon, 10 Aug 2015 22:06:30 -0400 Received: from mail-pd0-f173.google.com ([209.85.192.173]:34364 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752265AbbHKCG2 convert rfc822-to-8bit (ORCPT ); Mon, 10 Aug 2015 22:06:28 -0400 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Subject: Re: [RFC] bmac:change to use bitrev8() generic function From: yalin wang In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1CB77DC9@AcuExch.aculab.com> Date: Tue, 11 Aug 2015 10:06:23 +0800 Cc: Tobias Klauser , "fabf@skynet.be" , "david@gibson.dropbear.id.au" , "davem@davemloft.net" , "benh@kernel.crashing.org" , "netdev@vger.kernel.org" , open list Content-Transfer-Encoding: 8BIT Message-Id: <89DC2B55-8B16-4B35-8EE0-AAD912E273BA@gmail.com> References: <9A81C947-6F69-4549-B1D0-58061D6976CE@gmail.com> <20150810114901.GS16878@distanz.ch> <063D6719AE5E284EB5DD2968C1650D6D1CB77DC9@AcuExch.aculab.com> To: David Laight X-Mailer: Apple Mail (2.2098) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1303 Lines: 33 > On Aug 10, 2015, at 20:02, David Laight wrote: > >> From: Tobias Klauser >> Sent: 10 August 2015 12:49 >> On 2015-08-10 at 11:53:41 +0200, yalin wang wrote: >>> This change to use generic bitrev8() for bmac driver. > ... >>> @@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr) >>> >>> if (!(*addr)) return; >>> crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */ > > Why not *((u8 *)addr + 1) & 0x3f > >>> - crc = reverse6[crc]; /* Hyperfast bit-reversing algorithm */ >>> + crc = bitrev8((u8)crc); >> >> No, this won't work. reverse6 works on 6 bit values, while bitrev8 works >> on 8bit values, e.g. reverse6[1] = 0x20, while bitrev8(1) = 0x80 > > You could use bitrev8(n) >> 2. > > But that is a 'strange' map of a 7-bit value to a 6-bit one. > > I thought it was more common for ethernet hardware to use the > value of the crc register after all 6 bytes of the mac address > had been processed. oh, my mistake, i will change it in V2 for review.-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/