Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU

Bjorn Helgaas
2020-05-27T18:18:56Z

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.

> 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.

> Zhangfei Gao (2):
> PCI: Introduce PCI_FIXUP_IOMMU
> iommu: calling pci_fixup_iommu in iommu_fwspec_init
>
> drivers/iommu/iommu.c | 4 ++++
> drivers/pci/quirks.c | 7 +++++++
> include/asm-generic/vmlinux.lds.h | 3 +++
> include/linux/pci.h | 8 ++++++++
> 4 files changed, 22 insertions(+)
>
> --
> 2.7.4