On Wed, Jul 14, 2021 at 3:18 AM Jesper Dangaard Brouer <jbrouer@xxxxxxxxxx> wrote: > > > > On 14/07/2021 11.34, Yunsheng Lin wrote: > > As suggested by Alexander, "A DMA mapping should be page > > aligned anyway so the lower 12 bits would be reserved 0", > > so it might make more sense to repurpose the lower 12 bits > > of the dma address to store the frag count for frag page > > support in page pool for 32 bit systems with 64 bit dma, > > which should be rare those days. > > Do we have any real driver users with 32-bit arch and 64-bit DMA, that > want to use this new frag-count system you are adding to page_pool? > > This "lower 12-bit use" complicates the code we need to maintain > forever. My guess is that it is never used, but we need to update and > maintain it, and it will never be tested. > > Why don't you simply reject using page_pool flag PP_FLAG_PAGE_FRAG > during setup of the page_pool for this case? > > if ((pool->p.flags & PP_FLAG_PAGE_FRAG) && > (sizeof(dma_addr_t) > sizeof(unsigned long))) > goto reject-setup; > > That sounds good to me if we want to go that route. It would simplify this quite a bit since essentially we could just drop these if blocks. Thanks. - Alex
