Messages in this thread | | | Date | Fri, 31 Aug 2012 12:40:11 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in xen_swiotlb_alloc_coherent. |
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On Fri, Aug 31, 2012 at 01:47:05PM +0100, David Vrabel wrote: > On 31/08/12 10:57, Stefano Panella wrote: > > When running 32-bit pvops-dom0 and a driver tries to allocate a coherent > > DMA-memory the xen swiotlb-implementation returned memory beyond 4GB. > > > > This caused for example not working sound on a system with 4 GB and a 64-bit > > compatible sound-card with sets the DMA-mask to 64bit. > > > > On bare-metal and the forward-ported xen-dom0 patches from OpenSuse a coherent > > DMA-memory is always allocated inside the 32-bit address-range by calling > > dma_alloc_coherent_mask. > > We should have the same behaviour under Xen as bare metal so: > > Acked-By: David Vrabel <david.vrabel@citrix.com> > > This does limit the DMA mask to 32-bits by passing it through an > unsigned long, which seems a bit sneaky...
so is the issue that we are not casting it from 'u64' to 'u32' (unsigned long) on 32-bit?
> > Presumably the sound card is capable of handling 64 bit physical > addresses (or it would break under 64-bit kernels) so it's not clear why > this sound driver requires this restriction. > > Is there a bug in the sound driver or sound subsystem where it's > truncating a dma_addr_t by assigning it to an unsigned long or similar? > > > --- a/drivers/xen/swiotlb-xen.c > > +++ b/drivers/xen/swiotlb-xen.c > > @@ -232,7 +232,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size, > > return ret; > > > > if (hwdev && hwdev->coherent_dma_mask) > > - dma_mask = hwdev->coherent_dma_mask; > > + dma_mask = dma_alloc_coherent_mask(hwdev, flags); > > Suggest > > if (hwdev) > dma_mask = dma_alloc_coherent_mask(hwdev, flags)
Isn't that code just doing this: atic inline unsigned long dma_alloc_coherent_mask(struct device *dev, gfp_t gfp) { unsigned long dma_mask = 0;
dma_mask = dev->coherent_dma_mask; if (!dma_mask) dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : DMA_BIT_MASK(32);
return dma_mask; }
and in our code, the dma_mask by default is DMA_BIT_MASK(32):
u64 dma_mask = DMA_BIT_MASK(32);
So what I am missing?
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