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 81B04C76191 for ; Thu, 18 Jul 2019 08:56:49 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 3A5432173E for ; Thu, 18 Jul 2019 08:56:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3A5432173E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45q7Kq0zZqzDqLp for ; Thu, 18 Jul 2019 18:56:47 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (mailfrom) smtp.mailfrom=lst.de (client-ip=213.95.11.211; helo=verein.lst.de; envelope-from=hch@lst.de; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=lst.de Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 45q79Z3bx3zDqX2 for ; Thu, 18 Jul 2019 18:49:38 +1000 (AEST) Received: by verein.lst.de (Postfix, from userid 2407) id CF83D68B05; Thu, 18 Jul 2019 10:49:34 +0200 (CEST) Date: Thu, 18 Jul 2019 10:49:34 +0200 From: Christoph Hellwig To: Oliver O'Halloran Subject: Re: [PATCH] powerpc/dma: Fix invalid DMA mmap behavior Message-ID: <20190718084934.GF24562@lst.de> References: <20190717235437.12908-1-shawn@anastas.io> <8b6963ac-521a-5752-2cfb-bcd87cad9dc4@ozlabs.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) 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: Alexey Kardashevskiy , linuxppc-dev , Shawn Anastasio , Christoph Hellwig , Sam Bobroff Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Jul 18, 2019 at 01:45:16PM +1000, Oliver O'Halloran wrote: > > Other than m68k, mips, and arm64, everybody else that doesn't have > > ARCH_NO_COHERENT_DMA_MMAP set uses this default implementation, so > > I assume this behavior is acceptable on those architectures. > > It might be acceptable, but there's no reason to use pgport_noncached > if the platform supports cache-coherent DMA. > > Christoph (+cc) made the change so maybe he saw something we're missing. I always found the forcing of noncached access even for coherent devices a little odd, but this was inherited from the previous implementation, which surprised me a bit as the different attributes are usually problematic even on x86. Let me dig into the history a bit more, but I suspect the righ fix is to default to cached mappings for coherent devices.