Re: [PATCH v3 0/4] PCI: get DMA configuration from parent device

Arnd Bergmann
2015-01-08T22:27:14Z

On Thursday 08 January 2015 09:56:39 Arnd Bergmann wrote:
> There is another interesting case, which is a USB host controller or
> something similar behind a PCI bus. These are quite common and also
> need to be handled in some form. Let's do just PCI first for now, but
> be aware that this will come next. Should we assume that the ID that
> is required for a device is either known from the device node, or
> that it comes from a PCI device? That means for the USB case, we will
> likely need to have some custom logic. There seems to be an implicit
> assumption all over the kernel that all devices have the same IOMMU
> instance, but we can't really rely on that here.
>

Update: I've checked the USB implementation and we are lucky because
these interactions are all done by the USB host controller, and a
USB device is not itself DMA capable. We don't have to do anything
for USB.

Arnd