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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 61598C433DB for ; Tue, 16 Mar 2021 18:10:53 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 744D565127 for ; Tue, 16 Mar 2021 18:10:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 744D565127 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4F0Ltz0nccz3bs5 for ; Wed, 17 Mar 2021 05:10:51 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4F0Ltb3xDYz2xgK for ; Wed, 17 Mar 2021 05:10:27 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4F0LtQ5qpxz9v0hq; Tue, 16 Mar 2021 19:10:22 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id b9cIQnu_A5rj; Tue, 16 Mar 2021 19:10:22 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4F0LtQ3h1Nz9v0hm; Tue, 16 Mar 2021 19:10:22 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 2FFD98B7EE; Tue, 16 Mar 2021 19:10:24 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id pg33Skpor4nr; Tue, 16 Mar 2021 19:10:24 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B55658B7E1; Tue, 16 Mar 2021 19:10:23 +0100 (CET) Subject: Re: [PATCH] net: ethernet: fs-enet: remove casting dma_alloc_coherent To: David Laight , Xu Wang , "pantelis.antoniou@gmail.com" , "davem@davemloft.net" , "kuba@kernel.org" , "linuxppc-dev@lists.ozlabs.org" References: <20201211085212.85457-1-vulab@iscas.ac.cn> <34548188-67f4-d3ef-c2e3-871fc520e838@csgroup.eu> <6fc4b62ee7754d78b8f7b9c2275bc47e@AcuMS.aculab.com> <4a1c2852-781f-e125-afcb-69387660b6af@csgroup.eu> <3f31140339c94652b1e7116e91cfd9c8@AcuMS.aculab.com> From: Christophe Leroy Message-ID: <7f322df3-80b6-dfd0-caf2-afc2ca3950b1@csgroup.eu> Date: Tue, 16 Mar 2021 19:10:19 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <3f31140339c94652b1e7116e91cfd9c8@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-kernel@vger.kernel.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 11/12/2020 à 17:55, David Laight a écrit : > From: Christophe Leroy >> Sent: 11 December 2020 16:43 >> >> Le 11/12/2020 à 17:07, David Laight a écrit : >>> From: Christophe Leroy >>>> Sent: 11 December 2020 15:22 >>>> >>>> Le 11/12/2020 à 09:52, Xu Wang a écrit : >>>>> Remove casting the values returned by dma_alloc_coherent. >>>> >>>> Can you explain more in the commit log ? >>>> >>>> As far as I can see, dma_alloc_coherent() doesn't return __iomem, and ring_base member is __iomem >>> >>> Which is probably wrong - that is the kernel address of kernel memory. >>> So it shouldn't have the __iomem marker. >> >> That's where the buffer descriptors are, the driver accesses to the content of the buffer >> descriptors using the IO accessors in_be16()/out_be16(). Is it not correct ? > > I've just been looking at the crap in there. > My understanding is that IO accessors are for IO devices (eg addresses > from io_remap() etc). > > Buffers allocated by dma_alloc_coherent() are normal kernel memory > and don't need any accessors. > Now you might need some barriers - mostly because an ethernet chip > can typically read a ring entry without being prodded. > IIRC there is a barrier in writel() to ensure the dma master will > 'see' all memory writes done before the IO write that kicks it into > doing some processing. As far as I can see, writel() is using __iomem memory, see https://elixir.bootlin.com/linux/v5.12-rc2/source/include/asm-generic/io.h#L221 > > The fact that the driver contains so many __iomem casts (eg in > tx_restart) is an indication that something is badly awry. > __iomem exists to check you are using the correct type of pointer. > Any __iomem casts are dubious. I agree, but what else can we do to guarantee proper access to that memory ? Christophe