linux-kernel - Re: [PATCH 2.6.26] PCI: refuse to re-add a device to a bus upon pci_scan_child

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Date:	Tue, 22 Jul 2008 11:21:06 +0300
From:	"eran liberty" <eran.liberty@...il.com>
To:	"Matthew Wilcox" <matthew@....cx>
Cc:	"Eran Liberty" <liberty@...ricom.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH 2.6.26] PCI: refuse to re-add a device to a bus upon pci_scan_child_bus()

> I think this is your real problem, that you're rescanning the entire
> bus.  I don't think that's the route we'd recommend taking.
>

My stating point was that I have loaded a new design into a
programmable device which sits on the pci device. The new design can
implement numerous pci devices or non at all. I can think of an easy
way (or clean one) to scan only the programmable device. Scanning the
whole bus seemed reasonable.

> Why don't you call pci_scan_slot() instead?  You won't get the benefit of
> pcibios_fixup_bus(), but I'm not convinced that's safe to call on a bus
> that's already been scanned.
>

As said its not exactly a slot its more like a regular pci device that
someone suddenly welded into the pci bus. Its not a hotplug as well,
and I do not want to give up on the pcibios_fixup_bus()

As it is, with my patch applied i successfully go over the bus and
remove my own devices before I reprogram the
programmable device.

while ((dev = pci_get_device(PCI_VENDOR_ID_MYCOMP,PCI_DEVICE_ID_MYDEV,NULL))
!= NULL) {
	pci_remove_bus_device(dev);
	pci_dev_put(dev);
}

Load a new design into it.

Then scan the entire bus and add the newly discovered devices.

bus = null;
while ((bus = pci_find_next_bus(bus)) != NULL) {
	pci_scan_child_bus(bus);
	pci_bus_assign_resources(bus);
	pci_bus_add_devices(bus);
}

As seen here, this sequence of instructions seems very intuitive. It
will fail without the patch upon pci_bus_add_devices().

Liberty
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