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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 95AB1C433DB for ; Tue, 16 Mar 2021 08:00:28 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 487F164F77 for ; Tue, 16 Mar 2021 08:00:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 487F164F77 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 0442443199; Tue, 16 Mar 2021 08:00:27 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 4skvfME-ADrW; Tue, 16 Mar 2021 08:00:26 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp2.osuosl.org (Postfix) with ESMTP id 39F9E431A5; Tue, 16 Mar 2021 08:00:18 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 113F6C0010; Tue, 16 Mar 2021 08:00:18 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id EBE6CC000D for ; Tue, 16 Mar 2021 08:00:16 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id D43624EC89 for ; Tue, 16 Mar 2021 08:00:16 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bhE2R8GGfTo7 for ; Tue, 16 Mar 2021 08:00:16 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by smtp4.osuosl.org (Postfix) with ESMTPS id 0CA804EC2F for ; Tue, 16 Mar 2021 08:00:15 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 75A4D68C4E; Tue, 16 Mar 2021 09:00:09 +0100 (CET) Date: Tue, 16 Mar 2021 09:00:08 +0100 From: Christoph Hellwig To: Logan Gunthorpe Subject: Re: [RFC PATCH v2 07/11] dma-mapping: Add flags to dma_map_ops to indicate PCI P2PDMA support Message-ID: <20210316080008.GC15949@lst.de> References: <20210311233142.7900-1-logang@deltatee.com> <20210311233142.7900-8-logang@deltatee.com> <20210313023657.GC3402637@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Cc: linux-pci@vger.kernel.org, Dave Hansen , Ira Weiny , linux-nvme@lists.infradead.org, Stephen Bates , linux-mm@kvack.org, Jason Ekstrand , Ira Weiny , Christoph Hellwig , Minturn Dave B , Matthew Wilcox , Jason Gunthorpe , Daniel Vetter , John Hubbard , linux-block@vger.kernel.org, Dan Williams , Jakowski Andrzej , Xiong Jianxin , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Christian =?iso-8859-1?Q?K=F6nig?= X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Mar 15, 2021 at 10:33:13AM -0600, Logan Gunthorpe wrote: > >> + return !ops || ops->flags & DMA_F_PCI_P2PDMA_SUPPORTED; > > > > Is this logic correct? I would have expected. > > > > return (ops && ops->flags & DMA_F_PCI_P2PDMA_SUPPORTED); > > > If ops is NULL then the operations in kernel/dma/direct.c are used and > support is added to those in patch 6. So it is correct as written. It is not quite that easy. There also is the bypass flag and for the specific case where that is ignored the code needs a really good comment. And to assist that formatted so that it makes sense. The above line is indeed highly confusing even if it ends up being correct. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu