Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756056AbbLDQ7N (ORCPT ); Fri, 4 Dec 2015 11:59:13 -0500 Received: from mail-yk0-f179.google.com ([209.85.160.179]:36315 "EHLO mail-yk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755893AbbLDQ7L (ORCPT ); Fri, 4 Dec 2015 11:59:11 -0500 MIME-Version: 1.0 In-Reply-To: <20151204105000.GD10123@e104818-lin.cambridge.arm.com> References: <1448029226-4914-1-git-send-email-brian.starkey@arm.com> <20151204105000.GD10123@e104818-lin.cambridge.arm.com> Date: Fri, 4 Dec 2015 08:59:10 -0800 Message-ID: Subject: Re: [PATCH] drivers: dma-coherent: use ioremap_wc() for DMA_MEMORY_MAP From: Dan Williams To: Catalin Marinas Cc: Brian Starkey , Greg KH , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Arnd Bergmann 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: 2073 Lines: 43 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. -- 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/