On Thu, 15 Dec 2011, Felipe Balbi wrote:
> > > + if (req->dma == DMA_ADDR_INVALID) {
> >
> > What's the purpose of this test? Just to catch UDC drivers that try to
> > map a request twice in a row? If that's the case, then why not provide
> > an error message when it happens?
>
> The thing is that there has never been an agreement of who will do the
> final mapping on the Gadget Framework. Look at all UDCs and you'll see
> that they all have the same checks.
>
> We can add such a requirement now, but I'm afraid we could have
> out-of-tree gadget-drivers relying on dma_alloc_coherent() which would
> already give a request with a valid dma address. Or gadget drivers
> actually deciding to call dma_map_*() APIs.
Okay, I see.
> If more people would be willing to accept that possibility, I'm very
> eager to change the patch so that it would assume we have an unmapped
> request always. What do you say ?
I'm not too concerned about breaking out-of-tree drivers. After all,
the kernel doesn't have a stable internal ABI. Have you checked the
in-tree drivers? I haven't.
You could start off easy by leaving in the test and doing WARN_ONCE
if the DMA address is already set. Then if nothing shows up in
kerneloops, take it out entirely.
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
