From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:51214 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751275Ab0AXXwt (ORCPT ); Sun, 24 Jan 2010 18:52:49 -0500 Message-ID: <4B5CDD4A.5060800@iki.fi> Date: Mon, 25 Jan 2010 01:52:42 +0200 From: Antti Palosaari MIME-Version: 1.0 To: Jiri Slaby CC: Jiri Slaby , linux-kernel@vger.kernel.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Subject: Re: [PATCH 1/4] media: dvb/af9015, implement eeprom hashing References: <4B4F6BE5.2040102@iki.fi> <1264173055-14787-1-git-send-email-jslaby@suse.cz> <4B5C7258.1010605@iki.fi> <4B5C76B8.4090700@gmail.com> In-Reply-To: <4B5C76B8.4090700@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 01/24/2010 06:35 PM, Jiri Slaby wrote: > On 01/24/2010 05:16 PM, Antti Palosaari wrote: >>> + af9015_config.eeprom_sum = 0; >>> + for (reg = 0; reg< eeprom_size / sizeof(u32); reg++) { >>> + af9015_config.eeprom_sum *= GOLDEN_RATIO_PRIME_32; >>> + af9015_config.eeprom_sum += le32_to_cpu(((u32 *)eeprom)[reg]); >>> + } >>> + >>> + deb_info("%s: eeprom sum=%.8x\n", __func__, >>> af9015_config.eeprom_sum); >> >> Does this sum contain all 256 bytes from EEPROM? 256/4 is 64. > > Yes it does. It is computed as a hashed sum of 32-bit numbers (4 bytes) > -- speed (does not matter) and larger space of hashes. Hence the > division by 4. The cast does the trick: ((u32 *)eeprom)[reg] -- reg > index is on a 4-byte basis. OK, true. Anyhow, I don't know if this hashing formula is good enough - changing it later could be really pain. I compared it to the one used for em28xx driver and it was different. Could someone with better knowledge check that? Generally it is good and ready for submission. Acked-by: Antti Palosaari regards Antti -- http://palosaari.fi/