Re: Control message failures kill entire XHCI stack

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Hi Mathias,

Here's an interesting development:  as a result of a related thread on
linux-media, I came across a patch they are distributing in openelec:

https://github.com/OpenELEC/OpenELEC.tv/commit/b636927dec20652ff020e54ed7838a2e9be51e03

Now I'm not saying that reverting the commit in question is the
"right" thing to do, but I applied this patch and for the first time
in 100+ tests it started to work (i.e. I'm not seeing the XHCI hcd
tear down all the attached devices).

Given what I've seen of the bug I cannot really explain why the
scatter gather list sizes would have any bearing on TRBs for USB
control messages to be added to the queue.  Perhaps we're hitting the
upper bound of the list?  Any further speculation on my part would
just make me look clueless...

It would be great if you could offer any insight as to why the patch
in question could be responsible for the behavior we're seeing.  I
would really rather not just blindly check this patch into my local
tree and declare "victory" without understanding the underlying issue
and whether it's likely to cause other problems.

Devin

-- 
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com
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