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h=Subject:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:content-disposition; bh=oFF8o/RVegrG3G5YG5dTK44WOWDv57bdoGVgR2ktNWc=; b=dsqiw2UqRHpc2m6czITifyPazC l3KC3T9j57KTF3XoWiyV+LPgw4lbLtgOWKdd598bgRLfvrtkF2yuQDTcMKhGG9vB+KiBIJHVKMqOo mz5L+MEsdNsRbgo0gzz/8XPLL0CEathKtt+ZC61Qu6pAMYwbwCzqpb34Hfj+pEJnqN+lbJ6lzm9Ih wMlXJ7CnBmVPIFSao3qYHQjM/uSXXdMUZqbGyOWB+ccwh0ZmHoBC+XWjsMT4ETu8VxhHGEnyC4uu8 9v/yv+i4wmpSzCRFdT+0I+6inCilQdZbbQP3yiENwxiLiBsWDTPHNXrs7QPi+fZVB9gawHTLngfEt /Q9Irqsg==; Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.92) (envelope-from ) id 1lMC27-00012D-3W; Tue, 16 Mar 2021 09:54:59 -0600 To: Christoph Hellwig Cc: Robin Murphy , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Minturn Dave B , John Hubbard , Dave Hansen , Matthew Wilcox , =?UTF-8?Q?Christian_K=c3=b6nig?= , Jason Gunthorpe , Jason Ekstrand , Daniel Vetter , Dan Williams , Stephen Bates , Jakowski Andrzej , Xiong Jianxin References: <20210311233142.7900-1-logang@deltatee.com> <20210311233142.7900-7-logang@deltatee.com> <215e1472-5294-d20a-a43a-ff6dfe8cd66e@arm.com> <367fa81e-588d-5734-c69c-8cdc800dcb7e@deltatee.com> <20210316075821.GB15949@lst.de> From: Logan Gunthorpe Message-ID: <093b77cb-e8b1-c8a8-620b-ab36cdb7f3cc@deltatee.com> Date: Tue, 16 Mar 2021 09:54:53 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210316075821.GB15949@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: jianxin.xiong@intel.com, andrzej.jakowski@intel.com, sbates@raithlin.com, dan.j.williams@intel.com, daniel.vetter@ffwll.ch, jason@jlekstrand.net, jgg@ziepe.ca, christian.koenig@amd.com, willy@infradead.org, dave.hansen@linux.intel.com, jhubbard@nvidia.com, dave.b.minturn@intel.com, iommu@lists.linux-foundation.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, robin.murphy@arm.com, hch@lst.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH v2 06/11] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) X-Stat-Signature: 4yxmfsghtrcjgzpmrpup7wzwxo9y5gyr X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2D993E01615F Received-SPF: none (deltatee.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=ale.deltatee.com; client-ip=204.191.154.188 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615910110-323033 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021-03-16 1:58 a.m., Christoph Hellwig wrote: > On Fri, Mar 12, 2021 at 11:27:46AM -0700, Logan Gunthorpe wrote: >> So then we reject the patches that make that change. Seems like an odd >> argument to say that we can't do something that won't cause problems >> because someone might use it as an example and do something that will >> cause problems. Reject the change that causes the problem. > > No, the problem is a mess of calling conventions. A calling convention > returning 0 for error, positive values for success is fine. One returning > a negative errno for error and positive values for success is fine a well. > One returning 0 for the usual errors and negativ errnos for an unusual > corner case is just a complete mess. Fair enough. I can try implementing a dma_map_sg_p2p() roughly as Robin suggested that has a more reasonable calling convention. Most of your other feedback seems easy enough so I'll address it in a future series. Thanks, Logan