Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751827AbaKESPy (ORCPT ); Wed, 5 Nov 2014 13:15:54 -0500 Received: from smtp.citrix.com ([66.165.176.89]:31270 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750963AbaKESPv (ORCPT ); Wed, 5 Nov 2014 13:15:51 -0500 X-IronPort-AV: E=Sophos;i="5.07,321,1413244800"; d="scan'208";a="188436681" Date: Wed, 5 Nov 2014 18:15:38 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Catalin Marinas CC: Stefano Stabellini , Will Deacon , "xen-devel@lists.xensource.com" , "konrad.wilk@oracle.com" , "Ian.Campbell@citrix.com" , "david.vrabel@citrix.com" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v7 3/8] arm64: introduce is_device_dma_coherent In-Reply-To: <20141105165646.GN32700@e104818-lin.cambridge.arm.com> Message-ID: References: <1414422568-19103-3-git-send-email-stefano.stabellini@eu.citrix.com> <20141103105716.GC23162@arm.com> <20141105165646.GN32700@e104818-lin.cambridge.arm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Nov 2014, Catalin Marinas wrote: > On Mon, Nov 03, 2014 at 11:10:18AM +0000, Stefano Stabellini wrote: > > On Mon, 3 Nov 2014, Will Deacon wrote: > > > On Mon, Nov 03, 2014 at 10:46:03AM +0000, Stefano Stabellini wrote: > > > > On Mon, 27 Oct 2014, Stefano Stabellini wrote: > > > > > Introduce a boolean flag and an accessor function to check whether a > > > > > device is dma_coherent. Set the flag from set_arch_dma_coherent_ops. > > > > > > > > > > Signed-off-by: Stefano Stabellini > > > > > Signed-off-by: Catalin Marinas > > > > > CC: will.deacon@arm.com > > > > > > > > Will, Catalin, > > > > are you OK with this patch? > > > > > > It would be nicer if the dma_coherent flag didn't have to be duplicated by > > > each architecture in dev_archdata. Is there any reason not to put it in the > > > core code? > > > > Yes, there is a reason for it: if I added a boolean dma_coherent flag in > > struct device as Catalin initially suggested, what would be the default > > for each architecture? Where would I set it for arch that don't use > > device tree? > > You don't need to. An architecture that has coherent DMA always doesn't > need to do anything. One that has non-coherent DMA always only needs to > select HAVE_DMA_NONCOHERENT. One that has a mix of both needs to find a > way to set dev->dma_coherent. Since that's a new API you introduce, it > doesn't break any existing architectures. I am not sure that this is better than the current patch but I can see that this approach is not too controversial, so I am happy to go with whatever the maintainers prefer. > Note that if !is_device_dma_coherent(), it doesn't always mean that > standard cache maintenance would be enough (but that's a Xen problem, > not sure how to solve). It is a thorny issue indeed. Xen would need to know how to do non-standard cache maintenance operations. Otherwise we would need to resurrect XENFEAT_grant_map_identity (that I am reverting in this series) and be content with having CONFIG_XEN_DOM0 depend on CONFIG_ARM_LPAE. > diff --git a/arch/Kconfig b/arch/Kconfig > index 05d7a8a458d5..8462b2e7491b 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -203,6 +203,9 @@ config HAVE_DMA_ATTRS > config HAVE_DMA_CONTIGUOUS > bool > > +config HAVE_DMA_NONCOHERENT > + bool > + > config GENERIC_SMP_IDLE_THREAD > bool > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 89c4b5ccc68d..fd7d5522764c 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -40,6 +40,7 @@ config ARM > select HAVE_DMA_API_DEBUG > select HAVE_DMA_ATTRS > select HAVE_DMA_CONTIGUOUS if MMU > + select HAVE_DMA_NONCOHERENT if OF > select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) > select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU > select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL) > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 9532f8d5857e..eb7a5aa64e0e 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -46,6 +46,7 @@ config ARM64 > select HAVE_DMA_API_DEBUG > select HAVE_DMA_ATTRS > select HAVE_DMA_CONTIGUOUS > + select HAVE_DMA_NONCOHERENT > select HAVE_DYNAMIC_FTRACE > select HAVE_EFFICIENT_UNALIGNED_ACCESS > select HAVE_FTRACE_MCOUNT_RECORD > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > index 3b64d0bf5bba..7e827726b702 100644 > --- a/drivers/of/platform.c > +++ b/drivers/of/platform.c > @@ -183,6 +183,7 @@ static void of_dma_configure(struct device *dev) > * dma coherent operations. > */ > if (of_dma_is_coherent(dev->of_node)) { > + dev->dma_coherent = true; > set_arch_dma_coherent_ops(dev); > dev_dbg(dev, "device is dma coherent\n"); > } I think that this would need to be #ifdef'ed as it is possible to have OF support but no HAVE_DMA_NONCOHERENT (PPC?). > diff --git a/include/linux/device.h b/include/linux/device.h > index ce1f21608b16..e00ca876db01 100644 > --- a/include/linux/device.h > +++ b/include/linux/device.h > @@ -796,6 +796,7 @@ struct device { > > bool offline_disabled:1; > bool offline:1; > + bool dma_coherent:1; > }; I guess we would have to #ifdef CONFIG_HAVE_DMA_NONCOHERENT the dma_coherent flag, right? Otherwise architecures that do not select CONFIG_HAVE_DMA_NONCOHERENT (x86 for example) would end up with a flag in struct device that doesn't reflect the properties of the device (dma coherent devices with dev->dma_coherent == 0). Overall it is a lot of ifdefs for not so much code sharing. > static inline struct device *kobj_to_dev(struct kobject *kobj) > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index d5d388160f42..0bdffba2337d 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -78,6 +78,18 @@ static inline int is_device_dma_capable(struct device *dev) > return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE; > } > > +#ifdef CONFIG_HAVE_DMA_NONCOHERENT > +static inline int is_device_dma_coherent(struct device *dev) > +{ > + return dev->dma_coherent; > +} > +#else > +static inline int is_device_dma_coherent(struct device *dev) > +{ > + return 1 > +} > +#endif > + > #ifdef CONFIG_HAS_DMA > #include > #else -- 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/