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To:     Christoph Hellwig <hch@lst.de>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
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        Stephen Bates <sbates@raithlin.com>,
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        Don Dutile <ddutile@redhat.com>,
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        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: <20210513223203.5542-1-logang@deltatee.com>
 <20210513223203.5542-16-logang@deltatee.com> <20210514135712.GD4715@lst.de>
From:   Logan Gunthorpe <logang@deltatee.com>
Message-ID: <6615c351-9c28-3a74-8c43-4aeb7993fb98@deltatee.com>
Date:   Fri, 14 May 2021 10:17:48 -0600
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Subject: Re: [PATCH v2 15/22] dma-direct: Support PCI P2PDMA pages in
 dma-direct map_sg
Precedence: bulk


On 2021-05-14 7:57 a.m., Christoph Hellwig wrote:
>> +	for_each_sg(sgl, sg, nents, i) {
>> +		if (sg_is_dma_pci_p2pdma(sg)) {
>> +			sg_dma_unmark_pci_p2pdma(sg);
>> +		} else  {
> 
> Double space here.  We also don't really need the curly braces to start
> with.
> 
>> +	struct pci_p2pdma_map_state p2pdma_state = {};
>> +	enum pci_p2pdma_map_type map;
>>  	struct scatterlist *sg;
>> +	int i, ret;
>>  
>>  	for_each_sg(sgl, sg, nents, i) {
>> +		if (is_pci_p2pdma_page(sg_page(sg))) {
>> +			map = pci_p2pdma_map_segment(&p2pdma_state, dev, sg);
>> +			switch (map) {
> 
> Why not just:
> 
> 			switch (pci_p2pdma_map_segment(&p2pdma_state, dev,
> 					sg)) {
> 
> (even better with a shorter name for p2pdma_state so that it all fits on
> a single line)?
> 
>> +			case PCI_P2PDMA_MAP_BUS_ADDR:
>> +				continue;
>> +			case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
>> +				/*
>> +				 * Mapping through host bridge should be
>> +				 * mapped normally, thus we do nothing
>> +				 * and continue below.
>> +				 */
> 
> I have a bit of a hard time parsing this comment.
> 
>> +		if (sg->dma_address == DMA_MAPPING_ERROR) {
>> +			ret = -EINVAL;
>>  			goto out_unmap;
>> +		}
>>  		sg_dma_len(sg) = sg->length;
>>  	}
>>  
>> @@ -411,7 +443,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
>>  
>>  out_unmap:
>>  	dma_direct_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
>> -	return -EINVAL;
>> +	return ret;
> 
> Maybe just initialize ret to -EINVAL at declaration time to simplify this
> a bit?
>

All fair points, will fix in v3.

Logan