From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752960Ab2C1Oae (ORCPT ); Wed, 28 Mar 2012 10:30:34 -0400 Received: from smtp.fireflyinternet.com ([109.228.6.236]:18261 "EHLO fireflyinternet.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752007Ab2C1Oad (ORCPT ); Wed, 28 Mar 2012 10:30:33 -0400 X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.66.37; From: Chris Wilson Subject: Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() from gmbus transfers 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: <1332939117-6513-1-git-send-email-djkurtz@chromium.org> <1332939117-6513-15-git-send-email-djkurtz@chromium.org> <1332939924_127442@CP5-2952> Date: Wed, 28 Mar 2012 15:30:13 +0100 X-Originating-IP: 78.156.66.37 Message-ID: <1332945027_128384@CP5-2952> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 28 Mar 2012 21:21:42 +0800, Daniel Kurtz wrote: > On Wed, Mar 28, 2012 at 9:05 PM, Chris Wilson wrote: > > We do need the write flush here (and set_data) as the next action is a > > udelay loop which is not per-se a mb. > > Now I am confused. I915_WRITE_NOTRACE() calls writel(), which has an > explicit mb(); Why do you need another mb? Nominally writel isn't a memory barrier. I see that x86 does include mb in its writel define. However, if memory serves, that is only a write barrier to memory (equivalent of mfence), and not a PCI write flush/barrier for which we need to an explicit PCI read. -Chris -- Chris Wilson, Intel Open Source Technology Centre