Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932143AbaLHQu4 (ORCPT ); Mon, 8 Dec 2014 11:50:56 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:46424 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751520AbaLHQux (ORCPT ); Mon, 8 Dec 2014 11:50:53 -0500 Date: Mon, 8 Dec 2014 16:50:43 +0000 From: Catalin Marinas To: Arnd Bergmann Cc: Arend van Spriel , Russell King - ARM Linux , brcm80211-dev-list , linux-wireless , "linux-kernel@vger.kernel.org" , Will Deacon , Hante Meuleman , "hauke@hauke-m.de" , David Miller , "linux-arm-kernel@lists.infradead.org" , Marek Szyprowski Subject: Re: using DMA-API on ARM Message-ID: <20141208165042.GO16185@e104818-lin.cambridge.arm.com> References: <5481794E.4050406@broadcom.com> <2863746.4sUSEYqahB@wuerfel> <5485D054.7090109@broadcom.com> <2048819.2EPzBi8E3T@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2048819.2EPzBi8E3T@wuerfel> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 08, 2014 at 04:38:57PM +0000, Arnd Bergmann wrote: > On Monday 08 December 2014 17:22:44 Arend van Spriel wrote: > > >> The log: first the ring allocation info is printed. Starting at > > >> 16.124847, ring 2, 3 and 4 are rings used for device to host. In this > > >> log the failure is on a read of ring 3. Ring 3 is 1024 entries of each > > >> 16 bytes. The next thing printed is the kernel page tables. Then some > > >> OpenWRT info and the logging of part of the connection setup. Then at > > >> 1780.130752 the logging of the failure starts. The sequence number is > > >> modulo 253 with ring size of 1024 matches an "old" entry (read 40, > > >> expected 52). Then the different pointers are printed followed by > > >> the kernel page table. The code does then a cache invalidate on the > > >> dma_handle and the next read the sequence number is correct. > > > > > > How do you invalidate the cache? A dma_handle is of type dma_addr_t > > > and we don't define an operation for that, nor does it make sense > > > on an allocation from dma_alloc_coherent(). What happens if you > > > take out the invalidate? > > > > dma_sync_single_for_cpu(, DMA_FROM_DEVICE) which ends up invalidating > > the cache (or that is our suspicion). > > I'm not sure about that: > > static void arm_dma_sync_single_for_cpu(struct device *dev, > dma_addr_t handle, size_t size, enum dma_data_direction dir) > { > unsigned int offset = handle & (PAGE_SIZE - 1); > struct page *page = pfn_to_page(dma_to_pfn(dev, handle-offset)); > __dma_page_dev_to_cpu(page, offset, size, dir); > } > > Assuming a noncoherent linear (no IOMMU, no swiotlb, no dmabounce) mapping, > dma_to_pfn will return the correct pfn here, but pfn_to_page will return a > page pointer into the kernel linear mapping, Or a highmem page, both should be handled by dma_cache_maint_page(). > which is not the same > as the pointer you get from __alloc_remap_buffer(). The pointer that > was returned from dma_alloc_coherent is a) non-cachable, and b) not the > same that you flush here. Correct. But apart from the fact that you don't need to flush buffers allocated with dma_alloc_coherent(), the above sync_single would work on ARMv7 where the D-cache is PIPT, so the virtual address doesn't matter much as long as it maps the same physical address. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/