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SubjectRe: [Xen-devel] [PATCH 2/2] swiotlb-xen: xen_swiotlb_map_page: do not error out if dma_capable fails
On Tue, Nov 12, 2013 at 02:12:00PM +0000, Stefano Stabellini wrote:
> Many ARM devices do not set the dma_mask correctly today.
> As a consequence dma_capable fails for them regardless of the address
> passed to it.

Wouldn't the DMA API debug warn of bad usage.

> In xen_swiotlb_map_page we currently use dma_capable to check if the
> address returned by the swiotlb is good for dma for the device.

Right..
> However the check would often fail even if the address is correct.

.. and they will fail b/c the device hasn't set its dma mask so
we use the platform default right? What is the platform default?

> Considering that we know that the swiotlb buffer has a low address,
> skip the check.

I am not following that sentence. Could you please explain to me
how the SWIOTLB buffer low address guarantees that we don't need
the check?
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

What are the drivers that are busted. Does DMA API debug flag them?

Thanks!
> ---
> drivers/xen/swiotlb-xen.c | 7 -------
> 1 files changed, 0 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 1eac073..543e30b 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -402,13 +402,6 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
> map & ~PAGE_MASK, size, dir, attrs);
> dev_addr = xen_phys_to_bus(map);
>
> - /*
> - * Ensure that the address returned is DMA'ble
> - */
> - if (!dma_capable(dev, dev_addr, size)) {
> - swiotlb_tbl_unmap_single(dev, map, size, dir);
> - dev_addr = 0;
> - }
> return dev_addr;
> }
> EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);
> --
> 1.7.2.5
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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