[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v5 11/13] xen: introduce xen_alloc/free_coherent_pages
On Wed, 11 Sep 2013, Catalin Marinas wrote: > On Mon, Sep 09, 2013 at 05:46:59PM +0100, Stefano Stabellini wrote: > > On Mon, 9 Sep 2013, Catalin Marinas wrote: > > > >>> They could also happen in a DomU if we assign a physical device to it > > > >>> (and an SMMU is not available). > > > >> > > > >> The problem is that you don't necessarily know one kind of coherency > > > >> you > > > >> know for a physical device. As I said, we plan to do this DT-driven. > > > > > > > > OK, but if I call arm64_swiotlb_dma_ops.alloc passing the right > > > > arguments to it, I should be able to get the right coherency for the > > > > right device, correct? > > > > > > I think it needs a bit more work on the Xen part. Basically > > > dma_alloc_attrs() calls get_dma_ops() to obtain the best DMA operations > > > for a device. arm64_swiotlb_dma_ops is just the default implementation > > > and I'll add a _noncoherent variant as well. Default dma_ops will be > > > set to one of these during boot. But a device is also allowed to have > > > its own dev->archdata.dma_ops, set via set_dma_ops(). > > > > > > So even if you set the default dma_ops to Xen ops, you may not get them > > > via dma_alloc_coherent(). I don't see any easier solution other than > > > patching the dma_alloc_attrs() function to issue a Hyp call after the > > > memory has been allocated with the get_dma_ops()->alloc(). But I don't > > > like this either. > > > > I see. This problem affects arch/arm as well. > > Either we add an if (!xen_domain()) in get_dma_ops, or we could make > > get_dma_ops a function pointer and let people overwrite it. > > See below the first option implemented for arch/arm on top of the > > swiotlb series: > > > > > > diff --git a/arch/arm/include/asm/dma-mapping.h > > b/arch/arm/include/asm/dma-mapping.h > > index 7d6e4f9..0b8b5e4 100644 > > --- a/arch/arm/include/asm/dma-mapping.h > > +++ b/arch/arm/include/asm/dma-mapping.h > > @@ -12,6 +12,8 @@ > > #include <asm/memory.h> > > #include <asm/cacheflush.h> > > > > +#include <xen/xen.h> > > + > > #define DMA_ERROR_CODE (~0) > > extern struct dma_map_ops *dma_ops; > > extern struct dma_map_ops arm_dma_ops; > > @@ -19,7 +21,7 @@ extern struct dma_map_ops arm_coherent_dma_ops; > > > > static inline struct dma_map_ops *get_dma_ops(struct device *dev) > > { > > - if (dev && dev->archdata.dma_ops) > > + if (!xen_domain() && dev && dev->archdata.dma_ops) > > return dev->archdata.dma_ops; > > return dma_ops; > > } > > diff --git a/arch/arm/include/asm/xen/page-coherent.h > > b/arch/arm/include/asm/xen/page-coherent.h > > index af2cf8d..c2232fe 100644 > > --- a/arch/arm/include/asm/xen/page-coherent.h > > +++ b/arch/arm/include/asm/xen/page-coherent.h > > @@ -9,6 +9,8 @@ static inline void *xen_alloc_coherent_pages(struct device > > *hwdev, size_t size, > > dma_addr_t *dma_handle, gfp_t flags, > > struct dma_attrs *attrs) > > { > > + if (hwdev && hwdev->archdata.dma_ops) > > + return hwdev->archdata.dma_ops->alloc(hwdev, size, dma_handle, > > flags, attrs); > > return arm_dma_ops.alloc(hwdev, size, dma_handle, flags, attrs); > > I still don't like xen digging into the archdata internals. Me neither. > What about: > > diff --git a/arch/arm/include/asm/dma-mapping.h > b/arch/arm/include/asm/dma-mapping.h > index 5b579b9..5fa472c 100644 > --- a/arch/arm/include/asm/dma-mapping.h > +++ b/arch/arm/include/asm/dma-mapping.h > @@ -15,13 +15,20 @@ > extern struct dma_map_ops arm_dma_ops; > extern struct dma_map_ops arm_coherent_dma_ops; > > -static inline struct dma_map_ops *get_dma_ops(struct device *dev) > +static inline struct dma_map_ops *__get_dma_ops(struct device *dev) > { > if (dev && dev->archdata.dma_ops) > return dev->archdata.dma_ops; > return &arm_dma_ops; > } > > +static inline struct dma_map_ops *get_dma_ops(struct device *dev) > +{ > + if (xen_domain()) > + return xen_dma_ops; > + return __get_dma_ops(dev); > +} I agree that this is better. > static inline void set_dma_ops(struct device *dev, struct dma_map_ops *ops) > { > BUG_ON(!dev); > @@ -32,7 +39,7 @@ static inline void set_dma_ops(struct device *dev, struct > dma_map_ops *ops) > > static inline int dma_set_mask(struct device *dev, u64 mask) > { > - return get_dma_ops(dev)->set_dma_mask(dev, mask); > + return __get_dma_ops(dev)->set_dma_mask(dev, mask); > } > > #ifdef __arch_page_to_dma I don't understand the reason for this change though: shouldn't set_dma_mask go via the "default" (whatever that is), like the others? On native it won't make a difference, in any case it will end up calling arm_set_dma_mask. On Xen it would make a difference, because get_dma_ops(dev)->set_dma_mask would end up calling xen_swiotlb_set_dma_mask, that checks whether the mask is supported by the swiotlb buffer before setting the mask for the device, while obviously arm_set_dma_mask doesn't do that. > And in xen_alloc_coherent_pages(): > > return __get_dma_ops(dev).alloc(...); Right. > Alternatively, add the xen_domain() check in dma_alloc_attrs() instead > of get_dma_ops() (and other functions like map_sg etc.) I prefer this approach because it is going to be more concise. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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