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

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 25/10/14 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.
Thanks for the advices. I've managed to figure out that dma_map_single 
fails because dev->dma_mask was a NULL pointer. I've set it during probe 
with this:
dma_coerce_mask_and_coherent(&ndev->dev, DMA_BIT_MASK(32));

And the mappings seems to be set up properly (a bit below 512M), but the 
returned buffers are filled up with 0xAA, which I guess is probably some 
default value. Turning on and off CONFIG_ARM_LPAE did not helped.
I'll keep looking why is that, if you have an idea let me know.

Zoli

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