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Message-ID: <alpine.DEB.2.02.1410241828110.22875@kaball.uk.xensource.com>
Date: Fri, 24 Oct 2014 18:29:00 +0100
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: Stefano Stabellini <stefano.stabellini@...citrix.com>
CC: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <Will.Deacon@....com>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux@....linux.org.uk" <linux@....linux.org.uk>
Subject: Re: [PATCH v4 3/7] [RFC] arm/arm64: introduce is_dma_coherent
On Fri, 24 Oct 2014, Stefano Stabellini wrote:
> On Fri, 24 Oct 2014, Catalin Marinas wrote:
> > On Fri, Oct 24, 2014 at 12:39:59PM +0100, Stefano Stabellini wrote:
> > > On Fri, 24 Oct 2014, Catalin Marinas wrote:
> > > > 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.
> > >
> > > We don't have an additional device tracking struct on Xen.
> > > I agree that a new bit somewhere would be the best solution, but I am
> > > not sure where. Maybe in dev_archdata under arm and arm64? After all it
> > > is already used to keep pointers to dma and coherency related
> > > structures.
> >
> > I was thinking about something like below (maybe with some additional
> > ARCH_HAS_NONCOHERENT_DMA config for architectures that are always
> > coherent):
I don't think that introducing ARCH_HAS_NONCOHERENT_DMA is necessary here.
> > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > index 3b64d0bf5bba..ae399ccbd569 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 = 1;
> > set_arch_dma_coherent_ops(dev);
> > dev_dbg(dev, "device is dma coherent\n");
> > }
> > 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;
> > };
> >
> > 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..9c9ba5a5428e 100644
> > --- a/include/linux/dma-mapping.h
> > +++ b/include/linux/dma-mapping.h
> > @@ -78,6 +78,11 @@ static inline int is_device_dma_capable(struct device *dev)
> > return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE;
> > }
> >
> > +static inline int is_device_dma_coherent(struct device *dev)
> > +{
> > + return dev->dma_coherent;
> > +}
> > +
> > #ifdef CONFIG_HAS_DMA
> > #include <asm/dma-mapping.h>
> > #else
>
> This is probably the cleanest option. I am going to send it out and see
> what the comments are.
>
> I might still be able to request a backport if it doesn't make 3.18.
>
>
> > > However given the timing constraints I hope you would be OK with the
> > > suboptimal solution for now and create a common is_dma_coherent function
> > > in 3.19?
> >
> > If you want to push something for 3.18, you could have a temporary
> > solution but I would prefer a bool or something in the dev_archdata
> > structure. Another untested patch:
> >
> > diff --git a/arch/arm64/include/asm/device.h b/arch/arm64/include/asm/device.h
> > index cf98b362094b..243ef256b8c9 100644
> > --- a/arch/arm64/include/asm/device.h
> > +++ b/arch/arm64/include/asm/device.h
> > @@ -21,6 +21,7 @@ struct dev_archdata {
> > #ifdef CONFIG_IOMMU_API
> > void *iommu; /* private IOMMU data */
> > #endif
> > + bool dma_coherent;
> > };
> >
> > struct pdev_archdata {
> > diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
> > index adeae3f6f0fc..b6bc4c268878 100644
> > --- a/arch/arm64/include/asm/dma-mapping.h
> > +++ b/arch/arm64/include/asm/dma-mapping.h
> > @@ -54,11 +54,17 @@ static inline void set_dma_ops(struct device *dev, struct dma_map_ops *ops)
> >
> > static inline int set_arch_dma_coherent_ops(struct device *dev)
> > {
> > + dev->dev_archdata.dma_coherent = true;
> > set_dma_ops(dev, &coherent_swiotlb_dma_ops);
> > return 0;
> > }
> > #define set_arch_dma_coherent_ops set_arch_dma_coherent_ops
> >
> > +static inline int is_device_dma_coherent(struct device *dev)
> > +{
> > + return dev->dev_archdata.dma_coherent;
> > +}
> > +
> > #include <asm-generic/dma-mapping-common.h>
> >
> > static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
> >
> >
> > This way you don't have to test for swiotlb vs iommu ops (we don't have
> > the latter yet on arm64 but they are coming).
> >
> > --
> > Catalin
> >
>
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