Re: [PATCH v2 15/22] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg

[Logan Gunthorpe]

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