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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 911FDC3815B for ; Mon, 20 Apr 2020 14:13:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D7C120B1F for ; Mon, 20 Apr 2020 14:13:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727951AbgDTONN (ORCPT ); Mon, 20 Apr 2020 10:13:13 -0400 Received: from mail-out.m-online.net ([212.18.0.10]:37960 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725989AbgDTONN (ORCPT ); Mon, 20 Apr 2020 10:13:13 -0400 Received: from frontend01.mail.m-online.net (unknown [192.168.8.182]) by mail-out.m-online.net (Postfix) with ESMTP id 495TF26hvmz1rvm2; Mon, 20 Apr 2020 16:13:02 +0200 (CEST) Received: from localhost (dynscan1.mnet-online.de [192.168.6.70]) by mail.m-online.net (Postfix) with ESMTP id 495TDt16v3z1qtwV; Mon, 20 Apr 2020 16:13:02 +0200 (CEST) X-Virus-Scanned: amavisd-new at mnet-online.de Received: from mail.mnet-online.de ([192.168.8.182]) by localhost (dynscan1.mail.m-online.net [192.168.6.70]) (amavisd-new, port 10024) with ESMTP id aXeLBYzaK3PX; Mon, 20 Apr 2020 16:13:00 +0200 (CEST) X-Auth-Info: sZl4NKUfK90V2fjW5vtBPgnQ41ETpOjVNpiBfSmgj1Q= Received: from [IPv6:::1] (unknown [195.140.253.167]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.mnet-online.de (Postfix) with ESMTPSA; Mon, 20 Apr 2020 16:13:00 +0200 (CEST) Subject: Re: [PATCH V4 07/19] net: ks8851: Remove ks8851_rdreg32() To: Lukas Wunner Cc: netdev@vger.kernel.org, "David S . Miller" , Petr Stetiar , YueHaibing References: <20200414182029.183594-1-marex@denx.de> <20200414182029.183594-8-marex@denx.de> <20200420140700.6632hztejwcgjwsf@wunner.de> From: Marek Vasut Message-ID: <99104102-7973-e80f-9006-9a448403562b@denx.de> Date: Mon, 20 Apr 2020 16:12:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200420140700.6632hztejwcgjwsf@wunner.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 4/20/20 4:07 PM, Lukas Wunner wrote: > On Tue, Apr 14, 2020 at 08:20:17PM +0200, Marek Vasut wrote: >> The ks8851_rdreg32() is used only in one place, to read two registers >> using a single read. To make it easier to support 16-bit accesses via >> parallel bus later on, replace this single read with two 16-bit reads >> from each of the registers and drop the ks8851_rdreg32() altogether. >> >> If this has noticeable performance impact on the SPI variant of KS8851, >> then we should consider using regmap to abstract the SPI and parallel >> bus options and in case of SPI, permit regmap to merge register reads >> of neighboring registers into single, longer, read. > > Bisection has shown this patch to be the biggest cause of the performance > regression introduced by this series: Latency increases by about 9 usec. Just for completeness, did you perform this bisect on current linux-next without any patches except this series OR your patched rpi downstream vendor tree Linux 4.19 with preempt-rt patch applied ? [...]