On Thu, Jun 04, 2020 at 09:33:07PM +0800, Zhangfei Gao wrote: > On 2020/6/2 上午1:41, Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 09:33:44AM +0200, Joerg Roedel wrote: > > > On Wed, May 27, 2020 at 01:18:42PM -0500, Bjorn Helgaas wrote: > > > > Is this slowdown significant? We already iterate over every device > > > > when applying PCI_FIXUP_FINAL quirks, so if we used the existing > > > > PCI_FIXUP_FINAL, we wouldn't be adding a new loop. We would only be > > > > adding two more iterations to the loop in pci_do_fixups() that tries > > > > to match quirks against the current device. I doubt that would be a > > > > measurable slowdown. > > > I don't know how significant it is, but I remember people complaining > > > about adding new PCI quirks because it takes too long for them to run > > > them all. That was in the discussion about the quirk disabling ATS on > > > AMD Stoney systems. > > > > > > So it probably depends on how many PCI devices are in the system whether > > > it causes any measureable slowdown. > > I found this [1] from Paul Menzel, which was a slowdown caused by > > quirk_usb_early_handoff(). I think the real problem is individual > > quirks that take a long time. > > > > The PCI_FIXUP_IOMMU things we're talking about should be fast, and of > > course, they're only run for matching devices anyway. So I'd rather > > keep them as PCI_FIXUP_FINAL than add a whole new phase. > > > Thanks Bjorn for taking time for this. > If so, it would be much simpler. > > +++ b/drivers/iommu/iommu.c > @@ -2418,6 +2418,10 @@ int iommu_fwspec_init(struct device *dev, struct > fwnode_handle *iommu_fwnode, > fwspec->iommu_fwnode = iommu_fwnode; > fwspec->ops = ops; > dev_iommu_fwspec_set(dev, fwspec); > + > + if (dev_is_pci(dev)) > + pci_fixup_device(pci_fixup_final, to_pci_dev(dev)); > + > > Then pci_fixup_final will be called twice, the first in pci_bus_add_device. > Here in iommu_fwspec_init is the second time, specifically for iommu_fwspec. > Will send this when 5.8-rc1 is open. Wait, this whole fixup approach seems wrong to me. No matter how you do the fixup, it's still a fixup, which means it requires ongoing maintenance. Surely we don't want to have to add the Vendor/Device ID for every new AMBA device that comes along, do we? Bjorn
