linux-kernel - Re: [PATCH 0/2] Introduce PCI_FIXUP

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Date:   Thu, 28 May 2020 14:46:54 +0800
From:   Zhangfei Gao <zhangfei.gao@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        jean-philippe <jean-philippe@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        kenneth-lee-2012@...mail.com, Wangzhou <wangzhou1@...ilicon.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU

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.