From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from ns.horizon.com ([71.41.210.147]:31671 "HELO ns.horizon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752034AbaEOBPx (ORCPT ); Wed, 14 May 2014 21:15:53 -0400 Date: 14 May 2014 21:15:51 -0400 Message-ID: <20140515011551.26781.qmail@ns.horizon.com> (sfid-20140515_031622_901212_336E217B) From: "George Spelvin" To: hpa@zytor.com, linux@horizon.com, pavel@ucw.cz Subject: Re: [PATCH v2 1/3] lib/crc7: Shift crc7() output left 1 bit Cc: arik@wizery.com, david.gnedt@davizone.at, eliad@wizery.com, jan.nikitenko@gmail.com, laurent.pinchart+renesas@ideasonboard.com, linux-kernel@vger.kernel.org, linux-mmc@vger.kernel.org, linux-spi@vger.kernel.org, linux-wireless@vger.kernel.org, linville@tuxdriver.com, luca@coelho.fi, tony@atomide.com In-Reply-To: <53740C42.3000906@zytor.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: H. Peter Anvin wrote: > If the whole point of this is to use it for MMC/SD cards, why not just > also subsume the OR 1 and call it crc7_mmc() or something like that. > > (Which I'm all for doing... I don't know of any other crc7 users.) You'll find all users in my patch series. 2/3 updates the MMC card, while 3/3 hits drivers/net/wireless/ti/wl1251/spi.c and drivers/net/wireless/ti/wlcore/spi.c (which I'm pretty sure aren't MMC/SPI cards). Now, it turns out that they *also* set the lsbit (calling it WSPI_INIT_CMD_END). However, it's not possible to put that into the CRC table (it would mess up all bytes but the last), so an explicitly coded "| 1" is required at the end. Thic ends up being no saving at all to execution path length, and only moves one instruction from three drivers to shared code. While making it harder to read the drivers. A microscopic space saving (if and only if you have more than one of these drivers loaded) and no performance improvement didn't seem worth it to me.