Re: Question: multiple SMMUv3 devices probe

[richard clark <richard.xnu.clark@gmail.com>]

Jean-Philippe Brucker <jean-philippe@linaro.org> 于2021年4月13日周二 下午8:58写道：
>
> On Tue, Apr 13, 2021 at 08:40:47PM +0800, richard clark wrote:
> > >
> > > Hi,
> > >
> > > On Wed, Apr 07, 2021 at 05:37:52PM +0800, richard clark wrote:
> > > > Hi guys,
> > > > There're 3 SMMUv3 devices in my arm64 box. I am confused by the below
> > > > probe process:
> > > >
> > > > arm_smmu_device_probe(...) --> arm_smmu_set_bus_ops(&arm_smmu_ops):
> > > > if (platform_bus_type.iommu_ops != ops) {
> > > >         err = bus_set_iommu(&platform_bus_type, ops);
> > > >         if (err)
> > > > }
> > > >
> > > > so for the 1st smmu device on the platform_bus, the
> > > > arm_smmu_device_probe(...) will set the platform_bus_type.iommu_bus =
> > > > arm_smmu_ops, so for the arm_smmu_device_probe(...) when probing the
> > > > 2nd smmu device, the bus_set_iommu() will have no chance be called
> > > > since the platform_bus_type.iommu_bus == arm_smmu_ops is true, my
> > > > question is how the followed bus_set_iommu(...) being called?
> > >
> > > arm_smmu_ops is the same for all SMMU devices, so bus_set_iommu() only
> > > needs to be called once.
> > >
> > Actually, my question is a if pci device driver probes its device
> > before the SMMUv3 driver probing,
> > how does that pci device using the DMA with SMMU translation?
>
> It doesn't - by looking at the dependencies described in device-tree
(forget to reply all, so add the CC'ing...)
I understand 'it doesn't' here means the pci driver will not probe its
device before SMMU driver is on
> (iommu-map property) or in ACPI IORT, we defer probe of the PCI device
> until the SMMU is operational.
>
If that is correct, Jean, would you point me to the code snippet that
a pci driver will defer
its probe until the SMMU is functional? Some key points are enough...

> Thanks,
> Jean

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