From: David Brownell <david-b@pacbell.net>
To: linux-hotplug@vger.kernel.org
Subject: Re: [linux-usb-devel] [PATCH] fix some hubs and hid devices at startup
Date: Tue, 12 Mar 2002 22:15:05 +0000 [thread overview]
Message-ID: <marc-linux-hotplug-101597146126132@msgid-missing> (raw)
In-Reply-To: <marc-linux-hotplug-101588456410451@msgid-missing>
> > It doesn't make sense to me that if more delays are added in
> > the kernel code, userland needs to see even more.
>
> I agree, but Olaf and others prove that this works.
There was that hypothesis that it's really control traffic
interference ... I notice that usb_control_msg() chose
against the "keep the setup data in struct usb_device
and lock it with a semaphore" strategy (it kmallocs
the setup buffer), so I could see how that'd happen.
"usbmodules" asks the device for its config descriptor,
rather than reading /proc/bus/usb/BBB/DDD, so HCDs
that don't handle control queuing (I think OHCI behaves
there, and EHCI, but not the UHCIs) might suffer from
concurrent control messages from it and from HID ...
I think the best that can be done for now would be a
hack: add a lock in usb_device that must be held
by whoever submits a control request, and released
when that request completes. The non-hack solution
is to support control queuing in all HCDs.
What kind of lock? Maybe that binary semaphore.
Code that needs to issue control requests in_interrupt()
would need to be modified, as would usb_control_msg().
> I'm more puzzled why usbmodules is needing to talk to a device. I
> thought usbmodules was only for cold-plug stuff. Have any ideas?
Usbmodules is used to cope with /sbin/hotplug not providing
a complete interface descriptor dump: it only shows the first
of N inferface descriptors. With coldplug, it doesn't run, and
doesn't provide any descriptors at all -- so it must be used.
However, even for the hotplug case "usbmodules" gives a
more complete module list. In the case of an audio device
with a sound/ISO interface and a control/HID interface, it'll
pick up the HID.
- Dave
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next prev parent reply other threads:[~2002-03-12 22:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-11 22:08 [linux-usb-devel] [PATCH] fix some hubs and hid devices at startup Johannes Erdfelt
2002-03-12 0:20 ` David Brownell
2002-03-12 20:27 ` Greg KH
2002-03-12 20:29 ` Greg KH
2002-03-12 22:15 ` David Brownell [this message]
2002-03-12 22:52 ` Greg KH
2002-03-13 1:52 ` David Brownell
2002-03-14 13:21 ` Olaf Hering
2002-03-15 18:28 ` Greg KH
2002-05-15 20:25 ` David Brownell
2002-05-15 20:37 ` Olaf Hering
2002-05-15 21:37 ` Johannes Erdfelt
-- strict thread matches above, loose matches on Subject: below --
2002-05-15 20:08 Olaf Hering
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