linux-kernel - Re: Missing USB XHCI and EHCI reset for kexec

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Date:	Sat, 7 Jun 2014 21:09:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	linux-usb <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...el.com>
Subject: Re: Missing USB XHCI and EHCI reset for kexec

On Sun, 8 Jun 2014, Benjamin Herrenschmidt wrote:

> Looking at the code a bit more ... that xhci_shutdown() worries me.
> 
> It basically just whacks xhci_halt() and optionally reset() but nothing
> is done that I can see to ensure that we aren't concurrently
> doing things like queuing URBs, polling the root hub etc...
> 
> That's definitely not clean and while it might work (most of the time
> at least) on actual shutdown it's definitely not right for kexec I
> reckon.

Yes, it really was meant for actual system shutdown.

> Now there's a separate discussion that we had a while ago and might
> want to resume which is to say that kexec shouldn't be calling
> shutdown() anyway, but instead remove() on all drivers which is
> a much better code path for the purpose of leaving the device in
> a state where a driver can reconnect to it.
> 
> However, in the case of XHCI that leads to another issue described
> here:
> 
> http://marc.info/?l=linux-usb&m=139483181809062&w=2
> 
> For which there was little / no discussion at all... I suppose we could
> do a quirk but I don't think the problem is fundamentally
> specific to the TI chip, we should probably stop both root hubs
> before we halt both HCDs.

The issue described in that email seems valid to me.  Maybe the patch
should be resubmitted.  Now that xhci-hcd has changed maintainership,
the discussion might move forward.

In any case, you certainly can try testing with that patch installed.  
After all, xhci-hcd should work properly after a rmmod/modprobe 
sequence, and this is pretty much the same thing.

Alan Stern

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