Re: USB 3.0 in Linux main stream kernel

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On Thursday 29 January 2009, Matthew Dharm wrote:
> On Thu, Jan 29, 2009 at 12:57:13PM -0500, Alan Stern wrote:
> > On Thu, 29 Jan 2009, David Vrabel wrote:
> > > Alan Stern wrote:
> > > > Pushing scatterlists down to the HCD level would involve several
> > > > nontrivial changes to the code.  The issue of the buffer lengths is
> > > > just one of them, although it is perhaps the most vexing.
> > >
> > > I don't see where the complexity is.  The HCD simply fills the
> > > hardware's s-g list structures based on the s-g list in the URB.
> >
> > I didn't say it was complex; I said it was nontrivial.  That's because
> > the existing HCD code is already complicated and difficult to decipher.
> >
> > > Obviously, none of the existing HCDs can support s-g lists in this
> > > manner and should continue to only accept URBs without s-g lists.
> >
> > It's a little difficult to comprehend the intent behind this statement.
> > Are you saying that if somebody does implement s-g lists for URBs, none
> > of the existing HCDs should be changed to accept them?  In that case,
> > what use would they be?
>
> I think what he's saying (at least, what I read it to mean) was this:
> Existing HCDs would use the existing mechanism for s-g lists.  The new HCD
> to support USB 3.0, which (apparently) has more capability, would process
> the buffer list directly.  The usb_sg_* code would need to be changed to
> recognize a more capable HCD and pass the s-g list to that HCD for "direct"
> processing.

And nothing should really forbid implementing said support in [uoe]hci, if
anyone has the cycles.

-- 
Inaky
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