From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0107EC43387 for ; Tue, 15 Jan 2019 23:36:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB7CA20883 for ; Tue, 15 Jan 2019 23:36:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391462AbfAOXgp (ORCPT ); Tue, 15 Jan 2019 18:36:45 -0500 Received: from mga01.intel.com ([192.55.52.88]:48235 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728841AbfAOXgo (ORCPT ); Tue, 15 Jan 2019 18:36:44 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Jan 2019 15:36:43 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,483,1539673200"; d="scan'208";a="267422316" Received: from yoojae-mobl1.amr.corp.intel.com (HELO [10.7.153.143]) ([10.7.153.143]) by orsmga004.jf.intel.com with ESMTP; 15 Jan 2019 15:36:43 -0800 Subject: Re: [PATCH v10 06/12] peci: Add a PECI adapter driver for Aspeed AST24xx/AST25xx To: Joel Stanley Cc: devicetree , Ryan Chen , Andy Shevchenko , Arnd Bergmann , Andrew Jeffery , Greg Kroah-Hartman , OpenBMC Maillist , Linux Kernel Mailing List , James Feist , Vernon Mauery , Robin Murphy , Haiyue Wang References: <20190107214136.5256-1-jae.hyun.yoo@linux.intel.com> <20190107214136.5256-7-jae.hyun.yoo@linux.intel.com> From: Jae Hyun Yoo Message-ID: <17179a43-9ac7-366a-bfe6-044e80875a06@linux.intel.com> Date: Tue, 15 Jan 2019 15:36:43 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/15/2019 3:14 PM, Joel Stanley wrote: > On Tue, 15 Jan 2019 at 09:49, Jae Hyun Yoo wrote: >>>> + /** >>>> + * We check that the regmap works on this very first access, >>>> + * but as this is an MMIO-backed regmap, subsequent regmap >>>> + * access is not going to fail and we skip error checks from >>>> + * this point. >>> >>> Why do you use a regmap for this driver? AFAICT it has exclusive >>> ownership over the register range it uses, which is sometimes a reason >>> to use a regmap over a mmio region. >>> >>> I'm not sure if you've ever disassembled drivers/base/regmap/regmap.o, >>> but if you do you will find that a single mmio read turns into >>> hundreds of instructions. >>> >> >> No specific reason. regmap makes some overhead as you mentioned but it >> also provides some advantages on access simplification, endianness >> handling and register dump at run time. I would not insist using of >> regmap if you prefer using of raw readl and writel. Do you want replace >> regmap with readl and writel in this driver? > > I think that would be best. > > You raise some good points about the regmap API, and you're not alone > in using it for these reasons. We should look in to providing a > suitable API without the overhead, or making regmap more efficient for > the mmio case. > Okay. I'll rewrite this driver code using readl and writel instead of regmap mmio. Thanks again for your review! Regards, Jae