Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932927AbbLGQTd (ORCPT ); Mon, 7 Dec 2015 11:19:33 -0500 Received: from mail-yk0-f176.google.com ([209.85.160.176]:34734 "EHLO mail-yk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755844AbbLGQT2 (ORCPT ); Mon, 7 Dec 2015 11:19:28 -0500 MIME-Version: 1.0 In-Reply-To: <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> <20151207132823.GC13179@e106950-lin.cambridge.arm.com> Date: Mon, 7 Dec 2015 08:19:27 -0800 Message-ID: Subject: Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP From: Dan Williams To: Brian Starkey Cc: Catalin Marinas , Greg KH , Arnd Bergmann , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3027 Lines: 65 On Mon, Dec 7, 2015 at 5:28 AM, Brian Starkey wrote: > 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(). I don't see a problem adding a _WC option to memremap. The only difference is that it can't replace ioremap_wc. I.e. unlike _WB, and _WT case where ioremap_cache and ioremap_wt are now deprecated we'd have ioremap_wc continuing to live alongside memremap(..., MEMREMAP_WC). -- 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/