Re: [PATCH 11/14] PCI/P2PDMA: dma_map P2PDMA map requests that traverse the host bridge

Christoph Hellwig
2019-07-24T06:32:37Z

> struct dev_pagemap *pgmap = sg_page(sg)->pgmap;
> + struct pci_dev *client;
> + int dist;
> +
> + client = find_parent_pci_dev(dev);
> + if (WARN_ON_ONCE(!client))
> + return 0;
>
> + dist = upstream_bridge_distance(pgmap->pci_p2pdma_provider,
> + client, NULL);

Doing this on every mapping call sounds expensive..

> + if (WARN_ON_ONCE(dist & P2PDMA_NOT_SUPPORTED))
> + return 0;
> +
> + if (dist & P2PDMA_THRU_HOST_BRIDGE)
> + return dma_map_sg_attrs(dev, sg, nents, dir, attrs);
> + else
> + return __pci_p2pdma_map_sg(pgmap, dev, sg, nents);

Can't we organize the values so that we can switch on the return
value instead of doing flag checks?

> }
> EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg_attrs);
>
> @@ -847,6 +861,21 @@ EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg_attrs);
> void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
> int nents, enum dma_data_direction dir, unsigned long attrs)
> {
> + struct dev_pagemap *pgmap = sg_page(sg)->pgmap;
> + struct pci_dev *client;
> + int dist;
> +
> + client = find_parent_pci_dev(dev);
> + if (!client)
> + return;
> +
> + dist = upstream_bridge_distance(pgmap->pci_p2pdma_provider,
> + client, NULL);

And then we do it for every unmap again..