RE: 3.13-rc1 regression: Scatter-gather list issues at SuperSpeed only

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On Tue, 4 Mar 2014, David Laight wrote:

> > An alternative is to work around this particular problem by identifying
> > the code that submits the 3-sector SG element, and changing it to use
> > an even number of sectors.  But obviously that doesn't solve the
> > underlying issue.
> 
> Actually most of the block layer code could be taught to split requests
> into multiple URBs. Or even resubmit bounced requests split in two.
> Although splitting requests won't help the network code.

It won't help the mass-storage code either.  If an SG element is
shorter than the maxpacket length, splitting it up isn't going to make
it longer.

What _would_ help would be for the block layer to split up both this
element and the next one, and then allocate a maxpacket-sized bounce
buffer to hold the last part of this element plus the first part of the
next.

But _that_ won't help the network code.

Alan Stern

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