Re: USB and DMA on Alpha with 2.6.0-test7

[Jamie Lokier <jamie@shareable.org>]

Ivan Kokshaysky wrote:
> On Fri, Oct 10, 2003 at 11:22:06AM +0200, Måns Rullgård wrote:
> > Yesterday, I compiled 2.6.0-test7 for one of my Alpha boxes.  I have
> > an AX8817X based USB ethernet adaptor connected to it (it's short on
> > PCI slots), so I compiled the usbnet module.  When I loaded usbnet, I
> > got a BUG at include/asm-generic/dma-mapping.h:19.  Apparently, DMA
> > setup only works with PCI here.  How should this be fixed?  It worked
> > with -test4, albeit slowly, for other reasons.
> 
> Well, the usage of dma_supported() in usbnet.c is wrong even for i386.
> USB device doesn't do DMA, it's USB controller what does. The driver should
> check dma_mask of the parent device instead, something like this:
> 
> 	// possible with some EHCI controllers
> 	if (*udev->dev->parent->dma_mask == 0xffffffffffffffffULL)
> 		net->features |= NETIF_F_HIGHDMA;

Isn't the device's dma_mask set equal to the controller's dma_mask
automatically?

What happens if it's on a hub, or a hub on a hub?  Then the parent
isn't the controller, is it?

-- Jamie