On Wed, Sep 16, 2020 at 02:21:00PM -0300, Jason Gunthorpe wrote:
> + dma_addr = dma & ODP_DMA_ADDR_MASK;
> + if (dma_addr) {
>
> > But more importantly except for (dma_addr_t)-1 (DMA_MAPPING_ERROR)
> > all dma_addr_t values are valid, so taking more than a single bit
> > from a dma_addr_t is not strictly speaking correct.
>
> This is the result of dma_map_page(). The HW requires that
> dma_map_page(page_size) returns a DMA address that is page_size
> aligned, even for huge pages.
>
> So at least the last 12 bits of the DMA address are always 0, they can
> be used for flags. This is also the HW representation in the page
> table.
>
> Last time you pointed at this code you agreed this alignment was met,
> is it still OK?
True, the alignment actually makes this work. I'd still suggest to
throw in a comment about the actual usage.
