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To:     John Hubbard <jhubbard@nvidia.com>, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
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Cc:     Stephen Bates <sbates@raithlin.com>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
        Xiong Jianxin <jianxin.xiong@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
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        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>
From:   Logan Gunthorpe <logang@deltatee.com>
Message-ID: <4ad9c1d9-ec2a-1fe1-c5d9-19d2053da912@deltatee.com>
Date:   Mon, 3 May 2021 11:19:32 -0600
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Subject: Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for
 p2pdma pages
Precedence: bulk


On 2021-05-02 7:34 p.m., John Hubbard wrote:
>>   	if (iod->npages == 0)
>>   		dma_pool_free(dev->prp_small_pool, nvme_pci_iod_list(req)[0],
>>   			      iod->first_dma);
>> @@ -868,14 +857,13 @@ static blk_status_t nvme_map_data(struct nvme_dev *dev, struct request *req,
>>   	if (!iod->nents)
>>   		goto out_free_sg;
>>   
>> -	if (is_pci_p2pdma_page(sg_page(iod->sg)))
>> -		nr_mapped = pci_p2pdma_map_sg_attrs(dev->dev, iod->sg,
>> -				iod->nents, rq_dma_dir(req), DMA_ATTR_NO_WARN);
>> -	else
>> -		nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
>> -					     rq_dma_dir(req), DMA_ATTR_NO_WARN);
>> -	if (!nr_mapped)
>> +	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.

Logan