| Message ID | a758dfc6-2b00-e279-303c-ba1e27380e35@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Apr 11, 2017 at 01:43:28PM +0100, Julien Grall wrote: > On 11/04/17 02:14, Bart Van Assche wrote: > > On 04/10/17 17:31, Stefano Stabellini wrote: > >> I think the reason is that, as you can see, if (dev && dev->dma_ops), > >> dev->dma_ops is returned, while before this changes, xen_dma_ops was > >> returned on Xen on ARM. > >> > >> Unfortunately DMA cannot work properly without using the appropriate > >> xen_dma_ops. See drivers/xen/swiotlb-xen.c and arch/arm/xen/mm.c for > >> more details. (The problem is easy to spot, but I wasn't CC'ed on the > >> patch.) > >> > >> I don't know how to solve this problem without introducing some sort of > >> if (xen()) in include/linux/dma-mapping.h. > > > > Sorry but I don't have access to an ARM development system. Does your > > comment apply to dev == NULL only, dev != NULL only or perhaps to both? > > If your comment applies to dev != NULL only, can you check whether > > adding something like set_dma_ops(dev, get_arch_dma_ops(NULL)) to the > > appropriate ARM arch_setup_dma_ops() function is sufficient? > > If I understand correctly, set_dma_ops will replace dev->dma_ops with > Xen DMA ops. > > However, Xen DMA ops will need in some places to call the device > specific DMA ops (see __generic_dma_ops(...)). So I think replacing > dev->dma_ops is not a solution here. > > The hackish patch below is fixing the problem for both ARM64 and ARM32. > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index 0977317c6835..43a73ddeec7a 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -174,6 +174,8 @@ int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma, > #include <asm/dma-mapping.h> > static inline const struct dma_map_ops *get_dma_ops(struct device *dev) > { > + if (xen_initial_domain()) > + return xen_dma_ops; > if (dev && dev->dma_ops) > return dev->dma_ops; > return get_arch_dma_ops(dev ? dev->bus : NULL); If we do this, I guess there is no need to check for xen_initial_domain() in the get_arch_dma_ops() function. Anyway, this hunk would break the other architectures since xen_dma_ops is only defined for arm and arm64. > It is not nice as this is common code, but I can't find a better solution > so far. Any opinions? A different hack would be to avoid the generic get_dma_ops implementation on arm with some #ifdef hacks above. Yet another way would be for dom0 to always set dev->dma_ops to xen_dma_ops and preserve the real dma_ops somewhere under dev->archdata. You could intercept the arch_setup_dma_ops() function for this or use bus_register_notifier() (though I think the former is easier). The Xen code making use of the real dma_ops would have to dig them out from dev->archdata.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 0977317c6835..43a73ddeec7a 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -174,6 +174,8 @@ int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma, #include <asm/dma-mapping.h> static inline const struct dma_map_ops *get_dma_ops(struct device *dev) { + if (xen_initial_domain()) + return xen_dma_ops; if (dev && dev->dma_ops) return dev->dma_ops; return get_arch_dma_ops(dev ? dev->bus : NULL);