Messages in this thread | | | Date | Wed, 13 Nov 2002 18:06:06 +0000 | From | Nick Craig-Wood <> | Subject | Re: hotplug (was devfs) |
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On Wed, Nov 13, 2002 at 09:02:04AM -0800, Greg KH wrote: > On Wed, Nov 13, 2002 at 10:48:09AM +0000, Nick Craig-Wood wrote: > > > > We fixed these problems by removing hotplug and loading the relevant > > kernel modules in the correct order and voila a perfectly > > deterministic order for the /dev/ttyUSBs with all devices initialised. > > deterministic for you :)
Indeed! It was deterministic in the sense of
1) I booted the machine 10 times and the devices came up in the same order ;-)
2) the order of the devices was related to the usb topology, like this (these are usb bus positions as noted by hub.c)
1/1 <- hub1 1/1/1 <- keyspan 1 /dev/ttyUSB0..3 1/1/2 <- keyspan 2 /dev/ttyUSB4..7 1/1/3 <- keyspan 3 /dev/ttyUSB8..11 1/1/4 <- hub2 1/1/4/1 <- keyspan 4 /dev/ttyUSB12..15 1/1/4/2 <- keyspan 5 /dev/ttyUSB16..19 1/1/4/3 <- keyspan 6 /dev/ttyUSB20..23
That seemed like a sensible order to me!
> What hotplug will do is allow you to assign a /dev entry to a specific > device, so that you can go off of the topology, and not just the order > in which the devices are found. That is how this problem will be > solved properly.
So I'll be able to say usb bus1/1/4/1 port 3 should be /dev/ttyUSB15 and it will always be that port? That would be perfect.
> > Plugging in our USB bus with 24 devices on it does indeed produce a > > mini-forkbomb effect ;-) (Especially since these Keyspan devices are > > initialised twice - once without firmware and once with firmware.) > > > > So - perhaps hotplug ought to be serialised? > > No, it's not needed for this problem. There has been talk of > serializing stuff in userspace, which is the proper way to handle some > of the remove before add was seen problems.
Userspace serialisation would have solved this problem for us too I think without the extra mapping mechanism.
-- Nick Craig-Wood ncw1@axis.demon.co.uk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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