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

Murali Karicheri
2015-01-08T22:46:31Z

On 01/08/2015 05:27 PM, Arnd Bergmann wrote:
> 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.

Ok Thanks.

Murali
>
> Arnd
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--
Murali Karicheri
Linux Kernel, Texas Instruments