From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932590Ab2C1Ljd (ORCPT ); Wed, 28 Mar 2012 07:39:33 -0400 Received: from smtp.fireflyinternet.com ([109.228.6.236]:57647 "EHLO fireflyinternet.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932527Ab2C1Ljc (ORCPT ); Wed, 28 Mar 2012 07:39:32 -0400 X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.66.37; From: Chris Wilson Subject: Re: [PATCH 08/13 v4] drm/i915/intel_i2c: handle zero-length writes To: Daniel Kurtz Cc: Daniel Vetter , Keith Packard , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Benson Leung , Yufeng Shen In-Reply-To: References: <1332873382-29373-1-git-send-email-djkurtz@chromium.org> <1332873382-29373-9-git-send-email-djkurtz@chromium.org> <1332875657_117263@CP5-2952> Date: Wed, 28 Mar 2012 12:39:12 +0100 X-Originating-IP: 78.156.66.37 Message-ID: <1332934765_126523@CP5-2952> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 28 Mar 2012 19:32:27 +0800, Daniel Kurtz wrote: > Unfortunately there is a bug in both my original patch (it wasn't > incrementing loop), and in your suggested cleanup (it always > decrements len, even when it is already 0... or if the loop test > fails). How about the following; despite its pythonic nature, it > always completes with len holding the number of bytes remaining. > > val = loop = 0; > while (len && loop < 4) { > val |= *buf++ << (8 * loop++); > len -= 1; > } I'm getting over my aversion ;-) As we are here, have you considered doing an optimised u32 variant whilst len >= 4, which should be reasonably common during EDID transfer. Though I am not sure if that loop is merely in the noise compared to the rest of the mmio. -Chris -- Chris Wilson, Intel Open Source Technology Centre