> From: Alan Stern > On Wed, 8 Jan 2014, David Laight wrote: > > > > From: Alan Stern > > > > > > This may be a foolish question, but why is xhci-hcd using no-op TRBs in > > > the first place? > > > > Because it can't write in a link TRB because other parts of the > > code use link TRBs to detect the end of the ring. > > > > The problem is that it can't put a link TRB in the middle of > > a chain of data fragments unless it is at a 'suitable' offset > > from the start of the data TD. Given arbitrary input fragmentation > > this means that you can't put a link TRB in the middle of a TD. > > (The documented alignment might be as high as 16kB.) > > > > If the rest of the code used a 'ring end pointer' then a link TRB > > could be used instead. > > I see. Sounds like a poor design decision in hindsight. Can it be > changed? Anything can be changed :-) But it is a bit pervasive. Padding out with nops isolated the change. David -- 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
