From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 13 Apr 2018 00:20:46 +0200 (CEST) Received: from smtp.codeaurora.org ([198.145.29.96]:34970 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23993588AbeDLWUeGOcsD (ORCPT ); Fri, 13 Apr 2018 00:20:34 +0200 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 613FA60FB1; Thu, 12 Apr 2018 22:20:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1523571627; bh=t8fyu+cXciREdrVlOP2JsdBA8C6zHOCrJSaVY+6J/VE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=bo4ZiTbf6t71cOzQzXU1h24K58Gd9lgtlbpz6gAPSy4+mkPV9ZkgLzCdjqBO2NQca 1bRnm1WKDT9O+DrXTMDZ7B5ZZNEnFBALhKESGp0lPsLTzVnoiiUdetoKYeHZEG+uP7 pYYof1FMnJ/BAA9t/KD+ViRtiodEnsQogEVenKBs= Received: from [10.235.228.150] (global_nat1_iad_fw.qualcomm.com [129.46.232.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: okaya@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id 8BC1C60F90; Thu, 12 Apr 2018 22:20:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1523571626; bh=t8fyu+cXciREdrVlOP2JsdBA8C6zHOCrJSaVY+6J/VE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=gZai8mJog7dYjJF4/eQh8vHug93oPH//Bi3vr/vVRIdYd8hMB3e/fvwyKGGunNH4d jx485k6P6NTfZEChRRRRzQlAvJNaB0DKLkYHZhMTbgciSQKeVxeA73CpCB43ktDDYB KCO23OwNQ9hvG2bH4Yshu06/wqTua8ZAl1+t0/qE= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 8BC1C60F90 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=okaya@codeaurora.org Subject: Re: [PATCH v3 2/2] MIPS: io: add a barrier after register read in readX() To: James Hogan Cc: linux-mips@linux-mips.org, arnd@arndb.de, timur@codeaurora.org, sulrich@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Ralf Baechle , Paul Burton , linux-kernel@vger.kernel.org References: <1522760109-16497-1-git-send-email-okaya@codeaurora.org> <1522760109-16497-2-git-send-email-okaya@codeaurora.org> <20180412215149.GA27802@saruman> From: Sinan Kaya Message-ID: Date: Thu, 12 Apr 2018 18:20:16 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180412215149.GA27802@saruman> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 63514 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: okaya@codeaurora.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 4/12/2018 5:51 PM, James Hogan wrote: > But why don't we always use wmb() in the writeX() case? Might not the > cached write to DMA buffer be reordered with the uncached write to MMIO > register from the coherent DMA point of view? I'm waiting on feedback > from MIPS hardware folk on this topic. Are you asking about this? #if defined(CONFIG_CPU_CAVIUM_OCTEON) || defined(CONFIG_LOONGSON3_ENHANCEMENT) #define war_io_reorder_wmb() wmb() #else -#define war_io_reorder_wmb() do { } while (0) +#define war_io_reorder_wmb() barrier() #endif There is a write barrier in writeX() but seem to be different from platform to platform. I'm not familiar with the MIPS architecture. We can always use a wmb() but it could hurt performance where it is not needed. This is the kind of input we need from the MIPS folks if compiler barrier is enough or we need a wmb() for all cases. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.