Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU

[Zhangfei Gao]

Hi, Bjorn

On 2020/5/28 äå2:18, 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.