Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752489AbaKFKdu (ORCPT ); Thu, 6 Nov 2014 05:33:50 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:53794 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751534AbaKFKds (ORCPT ); Thu, 6 Nov 2014 05:33:48 -0500 Date: Thu, 6 Nov 2014 10:33:37 +0000 From: Catalin Marinas To: Stefano Stabellini Cc: 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 Message-ID: <20141106103337.GA19702@e104818-lin.cambridge.arm.com> References: <1414422568-19103-3-git-send-email-stefano.stabellini@eu.citrix.com> <20141103105716.GC23162@arm.com> <20141105165646.GN32700@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 On Wed, Nov 05, 2014 at 06:15:38PM +0000, Stefano Stabellini wrote: > 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. Functionally it is the same, but just less code duplication. > > 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. Is EL2 hyp or EL1 dom0 doing such maintenance? If the latter, you could just use the currently registered dma ops. > 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. So what does buy you? Is it just the hope that with LPAE you won't have weird system caches? > > 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?). The field is always there. But with !HAVE_DMA_NONCOHERENT, is_device_dma_coherent() would always return 1. You could avoid defining is_device_dma_coherent() entirely when !HAVE_DMA_NONCOHERENT, it wouldn't be worse than your patch in terms of an undefined function. > > 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). In my proposal you should not read this field directly but rather access it only via is_device_dma_coherent() (you can add a function for setting it as well). -- 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/