Re: [PATCH 0/4] USB & USBNET: loose DMA SG check and support usbnet DMA SG

Ming Lei
2013-07-31T11:55:18Z

On Wed, Jul 31, 2013 at 7:12 PM, Oliver Neukum <oneukum@suse.de> wrote:
> On Wed, 2013-07-31 at 18:51 +0800, Ming Lei wrote:
>> Hi,
>>
>> This patchset allows drivers to pass sg buffers which size can't be divided
>> by max packet size of endpoint if the host controllers support this kind
>> of sg buffers.
>
> Cool. One question though. It makes sense to use sg only
> if all elements are in memory capable of DMA. It seems to be possible
> to have HCs which can do unlimited sg but are limited to 32bit DMA.

For current usbnet devices which supports TSO, one header need to add
before skb->data from network stack, so basically the first two elements aren't
OK for other HCs(EHCI/UHCI/...) to DMA from SG.

Thanks,
--
Ming Le