high-order allocation + highmem + streaming DMA - possible?

Hello.

We are writing a driver for a custom PCI device that receives large amount
of data.

Device is capable of DMAing received data in 64k chunks.

We have been going to:
- use physically-continuous 64k-sized memory areas using alloc_pages() with
order=4,
- allocate large number of such areas on driver init,
- implement mmap() to map those all to userspace for zero-copy processing,
- use streaming DMA to actually receive data

However I can't find a way to use streaming DMA for large highmem areas.
- pci_map_single() is for linear mapping and can't work with highmem
- pci_map_page() can work with highmem but is limited to one page
- pci_map_sg() is for s/g lists, not for single 64k blocks.

Is there a way to use streaming DMA with large memory areas located in
highmem?
Or in this situation buffers in highmem can't be used?

Nikita
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