Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.34 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.34; helo=mail.nvidia.com;
Subject: Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for
 p2pdma pages
To:     Logan Gunthorpe <logang@deltatee.com>,
        <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>
CC:     Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Don Dutile <ddutile@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jakowski Andrzej <andrzej.jakowski@intel.com>,
        Minturn Dave B <dave.b.minturn@intel.com>,
        Jason Ekstrand <jason@jlekstrand.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Robin Murphy <robin.murphy@arm.com>
References: <20210408170123.8788-1-logang@deltatee.com>
 <20210408170123.8788-14-logang@deltatee.com>
 <78a165e1-657b-c284-d31a-adc8c9ded55d@nvidia.com>
 <4ad9c1d9-ec2a-1fe1-c5d9-19d2053da912@deltatee.com>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <92116e67-7388-aa31-cff3-71a7da82a731@nvidia.com>
Date:   Mon, 3 May 2021 17:26:57 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.10.0
MIME-Version: 1.0
In-Reply-To: <4ad9c1d9-ec2a-1fe1-c5d9-19d2053da912@deltatee.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 May 2021 00:26:58.5694
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 167a9abe-a59e-4567-3a56-08d90e93544b
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT037.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB3767
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 5/3/21 10:19 AM, Logan Gunthorpe wrote:
...
>>> +	nr_mapped = dma_map_sg_p2pdma_attrs(dev->dev, iod->sg, iod->nents,
>>> +				     rq_dma_dir(req), DMA_ATTR_NO_WARN);
>>> +	if (nr_mapped < 0) {
>>> +		if (nr_mapped != -ENOMEM)
>>> +			ret = BLK_STS_TARGET;
>>>    		goto out_free_sg;
>>> +	}
>>
>> But now the "nr_mapped == 0" case is no longer doing an early out_free_sg.
>> Is that OK?
> 
> dma_map_sg_p2pdma_attrs() never returns zero. It will return -ENOMEM in
> the same situation and results in the same goto out_free_sg.
> 

OK...that's true, it doesn't return zero. A comment or WARN or something
might be nice, to show that the zero case hasn't been overlooked. It's
true that the dma_map_sg_p2pdma_attrs() documentation sort of says
that (although not quite out loud).

thanks,
-- 
John Hubbard
NVIDIA