Re: [Qemu-devel] [PATCH] usb: Fix usb_packet_map() in the presence of IOMMUs

[Gerd Hoffmann <kraxel@redhat.com>]

On 09/26/12 04:59, David Gibson wrote:
> With the IOMMU infrastructure introduced before 1.2, we need to use
> dma_memory_map() to obtain a qemu pointer to memory from an IO bus address.
> However, dma_memory_map() alters the given length to reflect the length
> over which the used DMA translation is valid - which could be either more
> or less than the requested length.
> 
> usb_packet_map() does not correctly handle these cases, simply failing if
> dma_memory_map() alters the requested length.  If dma_memory_map()
> increased the length, we just need to use the requested length for the
> qemu_iovec_add().  However, if it decreased the length, it means that a
> single DMA translation is not valid for the whole sglist element, and so
> we need to loop, splitting it up into multiple iovec entries for each
> piece with a DMA translation (in practice >2 pieces is unlikely).
> 
> This patch implements the correct behaviour

Patch added to usb patch queue.

thanks,
  Gerd