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Message-ID: <Pine.LNX.4.44L0.1406072106360.6204-100000@netrider.rowland.org>
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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