On 2021/7/14 22:46, Alexander Duyck wrote: > 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. Ok, let's wait for a few day to see if there is anyone with 32-bit arch and 64-bit DMA system care enough to use the frag-count support in the page pool. > > Thanks. > > - Alex > . >
