Messages in this thread | | | Date | Wed, 8 Jan 2014 12:14:25 -0500 (EST) | From | Alan Stern <> | Subject | RE: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur within a USB payload burst |
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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?
Alan Stern
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