[PATCH] usb: ehci: fix update qtd->token in qh_append_tds

[Alan Stern]

On Sun, 28 Aug 2011, Ming Lei wrote:

> Looks like there is still another similar problem in qh_link_async():
> the last wmb
> should be changed into mb, because HC will read 'head->hw->hw_next' from qh
> descriptor and this pointer in qh is read only for HC. But this problem can't be
> observed on ARM, since wmb on ARM is same with mb.

It doesn't matter what the HC does -- the wmb() instruction is executed
by the CPU, not the HC.  The point of that instruction is to make sure 
that the

	qh->hw->hw_next = head->hw->hw_next;

line (and all the preceding lines as well) is ordered before the

	head->hw->hw_next = dma;
3C
line.  Since both of these lines are writes, not reads, it suffices to 
use wmb() rather than mb().

Alan Stern