From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH V2] net: ethernet: mellanox: correct page conversion Date: Mon, 18 Apr 2016 11:59:02 -0400 (EDT) Message-ID: <20160418.115902.1053705461620271779.davem@davemloft.net> References: <1460845412-13120-1-git-send-email-okaya@codeaurora.org> <20160418.000039.1946438541182822213.davem@davemloft.net> <87c17d3f979cf0167cd37077f39d0534@codeaurora.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, timur-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, cov-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: okaya-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org Return-path: In-Reply-To: <87c17d3f979cf0167cd37077f39d0534-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org From: okaya-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org Date: Mon, 18 Apr 2016 01:06:27 -0400 > On 2016-04-18 00:00, David Miller wrote: >> From: Sinan Kaya >> Date: Sat, 16 Apr 2016 18:23:32 -0400 >> >>> Current code is assuming that the address returned by >>> dma_alloc_coherent >>> is a logical address. This is not true on ARM/ARM64 systems. This >>> patch >>> replaces dma_alloc_coherent with dma_map_page API. The address >>> returned >>> can later by virtually mapped from the CPU side with vmap API. >>> Signed-off-by: Sinan Kaya >> You can't do this. >> The DMA map page API gives non-coherent mappings, and thus requires >> proper flushing. >> So a straight conversion like this is never legitimate. > > I would agree on proper dma api usage. However, the code is already > assuming coherent architecture by mapping the cpu pages as > page_kernel. > > Dma_map_page returns cached buffers and you don't need cache flushes > on coherent architecture to make the data visible. All you are telling me is that there are two bugs instead of one, so now both need to be fixed. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html