Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756569AbbLDRQC (ORCPT ); Fri, 4 Dec 2015 12:16:02 -0500 Received: from foss.arm.com ([217.140.101.70]:55682 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756380AbbLDRP7 (ORCPT ); Fri, 4 Dec 2015 12:15:59 -0500 Date: Fri, 4 Dec 2015 17:15:54 +0000 From: Catalin Marinas To: Dan Williams Cc: Greg KH , Arnd Bergmann , Brian Starkey , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP Message-ID: <20151204171554.GO10123@e104818-lin.cambridge.arm.com> References: <1448029226-4914-1-git-send-email-brian.starkey@arm.com> <20151204105000.GD10123@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 2857 Lines: 62 On Fri, Dec 04, 2015 at 08:59:10AM -0800, Dan Williams wrote: > On Fri, Dec 4, 2015 at 2:50 AM, Catalin Marinas wrote: > > On Fri, Nov 20, 2015 at 02:20:26PM +0000, Brian Starkey wrote: > >> When the DMA_MEMORY_MAP flag is used, memory which can be accessed > >> directly should be returned, so use ioremap_wc() instead of ioremap(). > >> Also, ensure that the correct memset operation is used in > >> dma_alloc_from_coherent() with respect to the region's flags. > >> > >> This fixes the below alignment fault on arm64, caused by invalid use > >> of memset() on Device memory. > > > > This is indeed affecting both arm32 and arm64 systems. > > > >> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c > >> index 55b8398..45358d0 100644 > >> --- a/drivers/base/dma-coherent.c > >> +++ b/drivers/base/dma-coherent.c > >> @@ -31,7 +31,10 @@ static int dma_init_coherent_memory(phys_addr_t phys_addr, dma_addr_t device_add > >> if (!size) > >> goto out; > >> > >> - mem_base = ioremap(phys_addr, size); > >> + if (flags & DMA_MEMORY_MAP) > >> + mem_base = ioremap_wc(phys_addr, size); > >> + else > >> + mem_base = ioremap(phys_addr, size); > > > > I wonder whether a memremap() approach for the DMA_MEMORY_MAP case would > > be better. This API was added recently by commit 92281dee825f ("arch: > > introduce memremap()"). It only supports write-back and write-through > > but we could add a MEMREMAP_WC flag for this case. > > I originally included both MEMREMAP_WC and MEMREAMP_UC as potential > flags to this api, but ultimately decided against it. The memremap() > api is meant for memory that is known to have no i/o side effects. As > far as I can see WC and UC usages are a muddy mix of "sometimes > there's I/O side effects, but it depends by arch and driver". In > other words we can't drop the "__iomem" annotation from WC and UC > mappings by default. In this context, the dma_declare_coherent_memory(DMA_MEMORY_MAP) implementation is aimed at normal RAM with no side effects as later returned by dma_alloc_coherent(). To me it looks like memremap is better suited here for the DMA_MEMORY_MAP case. As per the Documentation/DMA-API.txt: DMA_MEMORY_MAP - request that the memory returned from dma_alloc_coherent() be directly writable. which means no __iomem. Of course, we still need ioremap for DMA_MEMORY_IO which is supposed to be written with memcpy_toio() etc. Which memory type should be used is left to the driver and it should pass the corresponding DMA_MEMORY_* flag. -- 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/