Hi, Bjorn

On 2020/5/28 上午2:18, Bjorn Helgaas wrote:
On Tue, May 26, 2020 at 07:49:07PM +0800, Zhangfei Gao wrote:
Some platform devices appear as PCI but are actually on the AMBA bus,
and they need fixup in drivers/pci/quirks.c handling iommu_fwnode.
Here introducing PCI_FIXUP_IOMMU, which is called after iommu_fwnode
is allocated, instead of reusing PCI_FIXUP_FINAL since it will slow
down iommu probing as all devices in fixup final list will be
reprocessed, suggested by Joerg, [1]
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 do not notice the difference when compared fixup_iommu and fixup_final via get_jiffies_64,
since in our platform no other pci fixup is registered.

Here the plan is adding pci_fixup_device in iommu_fwspec_init,
so if using fixup_final the iteration will be done again here.

For example:
Hisilicon platform device need fixup in
drivers/pci/quirks.c handling fwspec->can_stall, which is introduced in [2]

+static void quirk_huawei_pcie_sva(struct pci_dev *pdev)
+    struct iommu_fwspec *fwspec;
+    pdev->eetlp_prefix_path = 1;
+    fwspec = dev_iommu_fwspec_get(&pdev->dev);
+    if (fwspec)
+        fwspec->can_stall = 1;
+DECLARE_PCI_FIXUP_IOMMU(PCI_VENDOR_ID_HUAWEI, 0xa250, quirk_huawei_pcie_sva);
+DECLARE_PCI_iFIXUP_IOMMU(PCI_VENDOR_ID_HUAWEI, 0xa251, quirk_huawei_pcie_sva);

[1] https://www.spinics.net/lists/iommu/msg44591.html
[2] https://www.spinics.net/lists/linux-pci/msg94559.html
If you reference these in the commit logs, please use lore.kernel.org
links instead of spinics.
Got it, thanks Bjorn.

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