Re: [PATCH v3 2/2] block-dma: properly take MMIO path

Christoph Hellwig
2025-10-27T07:49:34Z

> + switch (iter.p2pdma.map) {
> + case PCI_P2PDMA_MAP_BUS_ADDR:
> + iod->flags |= IOD_DATA_P2P;
> + break;
> + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> + iod->flags |= IOD_DATA_MMIO;
> + break;
> + default:
> + return BLK_STS_RESOURCE;

I almost wonder if we should just the pci_p2pdma_map_type values into
place. But that's a future cleanup, I'd rather get this going now.

> +static inline bool blk_rq_dma_unmap(struct request *req, struct device *dma_dev,
> + struct dma_iova_state *state, size_t mapped_len,
> + enum pci_p2pdma_map_type map)
> {
> - if (is_p2p)
> + if (map == PCI_P2PDMA_MAP_BUS_ADDR)
> return true;
>
> if (dma_use_iova(state)) {
> + unsigned int attrs = 0;
> +
> + if (map == PCI_P2PDMA_MAP_THRU_HOST_BRIDGE)
> + attrs |= DMA_ATTR_MMIO;
> +
> dma_iova_destroy(dma_dev, state, mapped_len, rq_dma_dir(req),
> - 0);
> + attrs);

The only thing in req that is used now is the data directrion. I'd be
almost tempted to just pass that and lift this to dma-mapping.h.

But I guess we could just do that in a follow on to not drag in
another subsystem.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>