Re: [RFC PATCH v1 18/18] nvme-pci: use new dma API

From: Robin Murphy
Date: Thu Jul 04 2024 - 11:24:14 EST


On 02/07/2024 10:09 am, Leon Romanovsky wrote:
[...]
+static inline dma_addr_t nvme_dma_link_page(struct page *page,
+ unsigned int poffset,
+ unsigned int len,
+ struct nvme_iod *iod)
{
- int i;
- struct scatterlist *sg;
+ struct dma_iova_attrs *iova = &iod->dma_map->iova;
+ struct dma_iova_state *state = &iod->dma_map->state;
+ dma_addr_t dma_addr;
+ int ret;
+
+ if (iod->dma_map->use_iova) {
+ phys_addr_t phys = page_to_phys(page) + poffset;

Yeah, there's no way this can possibly work. You can't do the dev_use_swiotlb() check up-front based on some overall DMA operation size, but then build that operation out of arbitrarily small fragments of different physical pages that *could* individually need bouncing to not break coherency.

Thanks,
Robin.

+
+ dma_addr = state->iova->addr + state->range_size;
+ ret = dma_link_range(&iod->dma_map->state, phys, len);
+ if (ret)
+ return DMA_MAPPING_ERROR;
+ } else {
+ dma_addr = dma_map_page_attrs(iova->dev, page, poffset, len,
+ iova->dir, iova->attrs);
+ }
+ return dma_addr;
+}