Re: [Xen-devel] dma_map_single returns 0 on ARM

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 27 Oct 2014, manish jaggi wrote:
> On 27 October 2014 02:09, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > Hi all,
> >
> > On 25/10/2014 15:11, Stefano Stabellini wrote:
> >>
> >> On Fri, 24 Oct 2014, Zoltan Kiss wrote:
> >>>
> >>> Hi,
> >>>
> >>> I'm trying to fire up the Ethernet port of a Hisilicon D01 board, and it
> >>> fails
> >>> when it wants to map the buffers to the device:
> >>>
> >>>                 phys = dma_map_single(&ndev->dev, priv->rx_buf[i],
> >>>                                 RX_BUF_SIZE, DMA_FROM_DEVICE);
> >>>
> >>> This returns 0, while running on bare metal it works. Does anyone has an
> >>> advice where should I look?
> >>
> >>
> >> dma_map_single should just be a wrapper around dma_ops->map_page that in
> >> dom0 is implemented by xen_swiotlb_map_page.
> >>  From looking at the code the issue appears to be that dma_capable
> >> returns false for your device.
> >>
> >> In any case even if dma_map_single returned a valid address, keep in
> >> mind that at the moment if the device is not dma coherent Linux needs
> >> to be compiled with CONFIG_ARM_LPAE to be able to cache flush the
> >> buffers correctly. But the failure in that case is a memory corruption
> >> after the dma request is completed.
> >
> >
> > There is no memory corruption if CONFIG_ARM_LPAE is not enabled. It will
> > make crash DOM0 because of a BUG_ON in the swiotlb code (checking truncation
> > between DMA and physical address). This would happen on platform where there
> > is ram bank above 4G and when a guest is booting.
> >
> One basic question, if a system has SMMU (IOMMU) enabled, would xen
> still use SWIOTLB for dom0?

At the moment yes. Eventually we'll be able to detect that a particular
device is protected by an SMMU and as a consequence we'll just call the
regular dma_ops calls for it.


> > This option is only necessary for 3.17. Using 3.16 will throw lots of
> > warning because netback is mapping multiple time the same grant. Linux 3.15
> > and backwards will be "safe".
> >
> > Regards,
> >
> > --
> > Julien Grall
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel