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
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