Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755975AbbLGN2a (ORCPT ); Mon, 7 Dec 2015 08:28:30 -0500 Received: from foss.arm.com ([217.140.101.70]:36996 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755637AbbLGN22 (ORCPT ); Mon, 7 Dec 2015 08:28:28 -0500 Date: Mon, 7 Dec 2015 13:28:24 +0000 From: Brian Starkey To: Catalin Marinas Cc: Dan Williams , Greg KH , Arnd Bergmann , "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: <20151207132823.GC13179@e106950-lin.cambridge.arm.com> References: <1448029226-4914-1-git-send-email-brian.starkey@arm.com> <20151204105000.GD10123@e104818-lin.cambridge.arm.com> <20151204171554.GO10123@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20151204171554.GO10123@e104818-lin.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3534 Lines: 78 On Fri, Dec 04, 2015 at 05:15:54PM +0000, Catalin Marinas wrote: >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. The DMA_MEMORY_MAP flag is pretty much a statement of "no side- effects", so as Catalin says it would fit OK here. That said, if it's not possible to deprecate ioremap_wc() in the same way as ioremap_cache() then I wonder if there's even much benefit in adding it to memremap(). > >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. > This can still be achieved without adding _WC to memremap(). I can look at adding _WC to memremap() if that's deemed the preferred approach, but if that isn't clear-cut, then it would be nice to get this bug fixed now and worry about adding it to memremap() later. -Brian >-- 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/