[PATCH 7/9] nvme-pci: convert the data mapping blk_rq_dma_map

[Leon Romanovsky]

On Tue, Jun 10, 2025 at 07:06:45AM +0200, Christoph Hellwig wrote:
> Use the blk_rq_dma_map API to DMA map requests instead of scatterlists.
> This removes the need to allocate a scatterlist covering every segment,
> and thus the overall transfer length limit based on the scatterlist
> allocation.
> 
> Instead the DMA mapping is done by iterating the bio_vec chain in the
> request directly.  The unmap is handled differently depending on how
> we mapped:
> 
>  - when using an IOMMU only a single IOVA is used, and it is stored in
>    iova_state
>  - for direct mappings that don't use swiotlb and are cache coherent no
>    unmap is needed at al

s/unmap is needed/unmap is not needed

>  - for direct mappings that are not cache coherent or use swiotlb, the
>    physical addresses are rebuild from the PRPs or SGL segments
> 
> The latter unfortunately adds a fair amount of code to the driver, but
> it is code not used in the fast path.
> 
> The conversion only covers the data mapping path, and still uses a
> scatterlist for the multi-segment metadata case.  I plan to convert that
> as soon as we have good test coverage for the multi-segment metadata
> path.
> 
> Thanks to Chaitanya Kulkarni for an initial attempt at a new DMA API
> conversion for nvme-pci, Kanchan Joshi for bringing back the single
> segment optimization, Leon Romanovsky for shepherding this through a
> gazillion rebases and Nitesh Shetty for various improvements.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/nvme/host/pci.c | 388 +++++++++++++++++++++++++---------------
>  1 file changed, 242 insertions(+), 146 deletions(-)

Thanks,
Reviewed-by: Leon Romanovsky <leonro at nvidia.com>