On Tue, Jul 30, 2013 at 09:59:16AM -0600, Bjorn Helgaas wrote: > On Tue, Jul 30, 2013 at 12:09 AM, Takao Indoh > <indou.takao at jp.fujitsu.com> wrote: > > (2013/07/29 23:17), Bjorn Helgaas wrote: > >> On Sun, Jul 28, 2013 at 6:37 PM, Takao Indoh <indou.takao at jp.fujitsu.com> wrote: > >>> (2013/07/26 2:00), Bjorn Helgaas wrote: > > >>>> My point about IOMMU and PCI initialization order doesn't go away just > >>>> because it doesn't fit "kdump policy." Having system initialization > >>>> occur in a logical order is far more important than making kdump work. > >>> > >>> My next plan is as follows. I think this is matched to logical order > >>> on boot. > >>> > >>> drivers/pci/pci.c > >>> - Add function to reset bus, for example, pci_reset_bus(struct pci_bus *bus) > >>> > >>> drivers/iommu/intel-iommu.c > >>> - On initialization, if IOMMU is already enabled, call this bus reset > >>> function before disabling and re-enabling IOMMU. > >> > >> I raised this issue because of arches like sparc that enumerate the > >> IOMMU before the PCI devices that use it. In that situation, I think > >> you're proposing this: > >> > >> panic kernel > >> enable IOMMU > >> panic > >> kdump kernel > >> initialize IOMMU (already enabled) > >> pci_reset_bus > >> disable IOMMU > >> enable IOMMU > >> enumerate PCI devices > >> > >> But the problem is that when you call pci_reset_bus(), you haven't > >> enumerated the PCI devices, so you don't know what to reset. > > > > Right, so my idea is adding reset code into "intel-iommu.c". intel-iommu > > initialization is based on the assumption that enumeration of PCI devices > > is already done. We can find target device from IOMMU page table instead > > of scanning all devices in pci tree. > > > > Therefore, this idea is only for intel-iommu. Other architectures need > > to implement their own reset code. > > That's my point. I'm opposed to adding code to PCI when it only > benefits x86 and we know other arches will need a fundamentally > different design. I would rather have a design that can work for all > arches. I agree. It makes sense to work on a design which works for all arches. And that's when I feel that handling this problem at IOMMU level makes more sense, if we can. Thanks Vivek
