Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756147AbaJXKrz (ORCPT ); Fri, 24 Oct 2014 06:47:55 -0400 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:48057 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755889AbaJXKrx (ORCPT ); Fri, 24 Oct 2014 06:47:53 -0400 Date: Fri, 24 Oct 2014 11:47:46 +0100 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" , "linux@arm.linux.org.uk" Subject: Re: [PATCH v4 3/7] [RFC] arm/arm64: introduce is_dma_coherent Message-ID: <20141024104746.GC1955@localhost> References: <1412941908-5850-3-git-send-email-stefano.stabellini@eu.citrix.com> <20141010120702.GI7755@arm.com> <20141013125725.GA19156@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 On Thu, Oct 23, 2014 at 03:22:27PM +0100, Stefano Stabellini wrote: > On Wed, 22 Oct 2014, Stefano Stabellini wrote: > > On Mon, 13 Oct 2014, Stefano Stabellini wrote: > > > On Mon, 13 Oct 2014, Will Deacon wrote: > > > > On Mon, Oct 13, 2014 at 12:16:14PM +0100, Stefano Stabellini wrote: > > > > > On Fri, 10 Oct 2014, Stefano Stabellini wrote: > > > > > > On Fri, 10 Oct 2014, Will Deacon wrote: > > > > > > > On Fri, Oct 10, 2014 at 12:51:44PM +0100, Stefano Stabellini wrote: > > > > > > > > Introduce a function to check whether a device is dma coherent. > > > > > > > > > > > > > > > > Signed-off-by: Stefano Stabellini > > > > > > > > CC: linux@arm.linux.org.uk > > > > > > > > CC: catalin.marinas@arm.com > > > > > > > > CC: will.deacon@arm.com > > > > > > > > CC: linux-arm-kernel@lists.infradead.org > > > > > > > > --- > > > > > > > > arch/arm/include/asm/dma-mapping.h | 6 ++++++ > > > > > > > > arch/arm64/include/asm/dma-mapping.h | 5 +++++ > > > > > > > > 2 files changed, 11 insertions(+) > > > > > > > > > > > > > > > > diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h > > > > > > > > index c45b61a..bededbb 100644 > > > > > > > > --- a/arch/arm/include/asm/dma-mapping.h > > > > > > > > +++ b/arch/arm/include/asm/dma-mapping.h > > > > > > > > @@ -126,6 +126,12 @@ static inline int set_arch_dma_coherent_ops(struct device *dev) > > > > > > > > set_dma_ops(dev, &arm_coherent_dma_ops); > > > > > > > > return 0; > > > > > > > > } > > > > > > > > + > > > > > > > > +static inline bool is_dma_coherent(struct device *dev) > > > > > > > > +{ > > > > > > > > + return (__generic_dma_ops(dev) == &arm_coherent_dma_ops); > > > > > > > > +} > > > > > > > > > > > > > > Hmm, what about the IOMMU ops? > > > > > > > > > > > > Maybe I should check __generic_dma_ops(dev) != &arm_dma_ops? > > > > > > Do you have any better suggestions? > > > > > > > > > > ping? > > > > > > > > Without any clear idea about why this is needed or how it's used, I don't > > > > have any better ideas. > > > > > > Thanks for the quick reply. > > > > > > It is used in dom0 to figure out whether the device is not coherent: in > > > that case Dom0 is going to issue an hypercall and Xen is going to > > > execute the required cache maintenance operations on Dom0's behalf. > > > > > > In practice for this use case iommu_dma_ops is not a problem, as the > > > device is never going to appear as being behind an SMMU in dom0. > > > > re-ping? > > I don't mean to be pushy but this series is required to fix a regression > that causes dom0 to crash when running as dom0 on Xen on ARM if > non-coherent devices are present on the platform. Sorry for ignoring it but I don't fully understand how Xen works, especially this DMA stuff. I recall some blogs you wrote but I don't have time to re-read them (and I'm on holiday next week). I think a better way would be some Xen hook around set_arch_dma_coherent_ops(). Does Xen have its own device tracking structures? If not, you may be able to add another bitfield to the kernel one. -- 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/