offest calculation from the dma_address

[alexnln]

Hello,

In pci.c, in nvme_setup_prps() offset is calculated from the dma address:
int offset = dma_addr & (page_size - 1);

Why not to use sg->offset?

I mean, what if hypothetical dma allocator returns non-page aligned addresses?
In such case offset would be wrong.

Thanks,
Alex