Messages in this thread | | | Date | Fri, 20 Feb 2004 14:30:58 -0500 (EST) | From | Alan Stern <> | Subject | Re: [linux-usb-devel] Re: [BK PATCH] USB update for 2.6.3 |
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Just to clear up a small disagreement...
On Fri, 20 Feb 2004, Linus Torvalds wrote:
> On Thu, 19 Feb 2004, David S. Miller wrote: > > On Fri, 20 Feb 2004 18:10:41 +1100 > > Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote: > > > > > Hrm... so if the USB device drivers are actually doing the dma mapping > > > themselves, it make sense for them to pass their own struct device, no ? > > > > That's right, at least that was the idea. > > No. That would be _fundamentally_ wrong. > > There's no way a USB device can do DMA in the first place. It has no DMA > controller, and no way to read/write memory except through the USB host. > > So it is the host - and only the host - that matters. Anything else is a > bug.
Both of you are right. Linus is right that USB devices don't do DMA. Ben is right that sometimes a USB device _driver_ will set up a DMA mapping. And of course, it is set up on behalf of the corresponding USB controller, so the controller's struct device would be passed.
Alan Stern
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