On Wed, Jul 31, 2013 at 11:15 PM, Eric Dumazet [off-list ref] wrote:

On Wed, 2013-07-31 at 16:02 +0200, Oliver Neukum wrote:

quoted

On Wed, 2013-07-31 at 21:50 +0800, Ming Lei wrote:

quoted

In the usbnet case, the driver already supports non-sg well. Actually,
all current drivers should support non-sg well because urb->sg wasn't
introduced for very long time. We can think it as a new feature or DMA
enhancement for xHCI controller.

If you mean buffer debounce for dma sg support on ehci/uhci/ohci/..,
maybe we need to discuss and evaluate further.

We cannot lie to the networking layer. Either we can do sg in hardware
or we cannot. This is unfortunately determined by the HC not the device
on the bus. How else but from the host driver would we get the
information?

Hmm, I would rather make sure SG is really supported before adding TSO
support.

TCP stack can build skb with fragments of any size, not multiple
of 512 or 1024 bytes.

For this SG buffer, only xHCI USB host controller supports it, and other
host controllers can't support it if they don't use bounce buffer, but usbnet
devices may be connected to all these host controllers.

This patchset only enables SG/TSO support when ax88179_178a device
connects to xHCI host controller.

Thanks,
--
Ming Lei