From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-fx0-f215.google.com ([209.85.220.215]:63101 "EHLO mail-fx0-f215.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754002Ab0AXQfM (ORCPT ); Sun, 24 Jan 2010 11:35:12 -0500 Message-ID: <4B5C76B8.4090700@gmail.com> Date: Sun, 24 Jan 2010 17:35:04 +0100 From: Jiri Slaby MIME-Version: 1.0 To: Antti Palosaari 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> In-Reply-To: <4B5C7258.1010605@iki.fi> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: 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. regards, -- js