RE: [PATCH 2/2] Revert "USBNET: ax88179_178a: enable tso if usb host supports sg dma"

[David Laight]

From: Alan Stern 
> On Fri, 7 Mar 2014, David Laight wrote:
> 
> > From: Mathias Nyman
> > > This reverts commit 3804fad45411b48233b48003e33a78f290d227c8.
> > >
> > > This commit, together with commit 247bf557273dd775505fb9240d2d152f4f20d304
> > > "xhci 1.0: Limit arbitrarily-aligned scatter gather." were
> > > origially added to get xHCI 1.0 hosts and usb ethernet ax88179_178a devices
> > > working together with scatter gather. xHCI 1.0 hosts pose some requirement on how transfer
> > > buffers are aligned, setting this requirement for 1.0 hosts caused USB 3.0 mass
> > > storage devices to fail more frequently.
> >
> > This patch doesn't need to be reverted.
> 
> Yes, it does.
> 
> > Provided the xhci driver doesn't set the flag to say that arbitrary scatter
> > gather is supported (ie usb_device_no_sg_constraint(dev->udev)) is false)
> > the ax88179_178a driver won't request transmits that need fragmenting.
> 
> True.  But xhci-hcd _will_ set the flag, because of patch 1 in this
> series.  In other words, patch 1 makes patch 2 necessary.

I was reading patch 2 first.
It would seem to be better to modify patch 1 - so it doesn't set the flag.
Then the changes are limited to the usb tree, and the change to net wouldn't
need to be reapplied in order to test scatter-gather when it is properly fixed.

	David



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/