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Date: Mon, 09 Feb 2009 16:01:17 -0700 (MST)
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To: alfred@FreeBSD.org
From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: pyunyh@gmail.com, src-committers@FreeBSD.org, thompsa@FreeBSD.org,
	svn-src-user@FreeBSD.org
Subject: Re: svn commit: r187978 - user/thompsa/usb/sys/dev/usb2/ethernet
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In message: <20090209223439.GP68801@elvis.mu.org>
            Alfred Perlstein <alfred@FreeBSD.org> writes:
: * M. Warner Losh <imp@bsdimp.com> [090201 21:24] wrote:
: > In message: <20090202051421.GE43513@michelle.cdnetworks.co.kr>
: >             Pyun YongHyeon <pyunyh@gmail.com> writes:
: > : On Sun, Feb 01, 2009 at 09:52:18PM -0700, M. Warner Losh wrote:
: > : > In message: <20090202044416.GC43513@michelle.cdnetworks.co.kr>
: > : >             Pyun YongHyeon <pyunyh@gmail.com> writes:
: > : > : On Sun, Feb 01, 2009 at 08:36:18PM -0700, M. Warner Losh wrote:
: > : > : > In message: <20090201213749.GJ32503@citylink.fud.org.nz>
: > : > : >             Andrew Thompson <thompsa@FreeBSD.org> writes:
: > : > : > : On Sun, Feb 01, 2009 at 02:28:08PM -0700, M. Warner Losh wrote:
: > : > : > : > In message: <200902010650.n116obU1045871@svn.freebsd.org>
: > : > : > : >             Andrew Thompson <thompsa@FreeBSD.org> writes:
: > : > : > : > : +	locked = mtx_owned(&sc->sc_mtx);
: > : > : > : > : +	if (!locked)
: > : > : > : > : +		AUE_LOCK(sc);
: > : > : > : > 
: > : > : > : > You do know this is racy, right?
: > : > : > : 
: > : > : > : Yea... It only get called unlocked during mii probe+attach so its fine.
: > : > : > : I havnt actaully checked if its ok to hold a mutex during
: > : > : > : mii_phy_probe() which would make this go away.
: > : > : > 
: > : > : > You hold GIANT when probe+attach, which means I think you can't
: > : > : 
: > : > : AFAIK this is not true on USB2 and I think this is reason why
: > : > : it have to lock/unlock dance in probe/attach.
: > : > 
: > : > It is a newbus requirement that all probe/attach routines have to be
: > : > called with GIANT held.
: > : > 
: > : 
: > : If this can be done on USB2 it would greatly simplify MII attach
: > : part as well as locks used in MII access routines in all USB2
: > : ethernet drivers. I vaguely remember I asked for this to HPS, but
: > : he seem to forget about it.
: > 
: > I'll take a look into the matter in more detail.  It is an absolute
: > requirement of newbus at the moment that any call to
: > device_probe_and_attach(), including bus_generic_attach().
: 
: Can some asserts be added?
: 
: Maybe under an additonal ifdef considering usb2 for a short time?

Are these not sufficient:

int
device_probe_child(device_t dev, device_t child)
{
	devclass_t dc;
	driverlink_t best = NULL;
	driverlink_t dl;
	int result, pri = 0;
	int hasclass = (child->devclass != NULL);

	GIANT_REQUIRED;
...