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SubjectRe: [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and .attach_dev
On Wed, Sep 30, 2020 at 06:26:30PM -0700, Nicolin Chen wrote:
> On Thu, Oct 01, 2020 at 12:56:46AM +0300, Dmitry Osipenko wrote:
> > 01.10.2020 00:32, Nicolin Chen пишет:
> > > On Thu, Oct 01, 2020 at 12:24:25AM +0300, Dmitry Osipenko wrote:
> > >> ...
> > >>>> It looks to me like the only reason why you need this new global API is
> > >>>> because PCI devices may not have a device tree node with a phandle to
> > >>>> the IOMMU. However, SMMU support for PCI will only be enabled if the
> > >>>> root complex has an iommus property, right? In that case, can't we
> > >>>> simply do something like this:
> > >>>>
> > >>>> if (dev_is_pci(dev))
> > >>>> np = find_host_bridge(dev)->of_node;
> > >>>> else
> > >>>> np = dev->of_node;
> > >>>>
> > >>>> ? I'm not sure exactly what find_host_bridge() is called, but I'm pretty
> > >>>> sure that exists.
> > >>>>
> > >>>> Once we have that we can still iterate over the iommus property and do
> > >>>> not need to rely on this global variable.
> > >>>
> > >>> I agree that it'd work. But I was hoping to simplify the code
> > >>> here if it's possible. Looks like we have an argument on this
> > >>> so I will choose to go with your suggestion above for now.
> > >>
> > >> This patch removed more lines than were added. If this will be opposite
> > >> for the Thierry's suggestion, then it's probably not a great suggestion.
> > >
> > > Sorry, I don't quite understand this comments. Would you please
> > > elaborate what's this "it" being "not a great suggestion"?
> > >
> >
> > I meant that you should try to implement Thierry's solution, but if the
> > end result will be worse than the current patch, then you shouldn't make
> > a v4, but get back to this discussion in order to choose the best option
> > and make everyone agree on it.
>
> I see. Thanks for the reply. And here is a sample implementation:
>
> @@ -814,12 +815,15 @@ static struct tegra_smmu *tegra_smmu_find(struct device_node *np)
> }
>
> static int tegra_smmu_configure(struct tegra_smmu *smmu, struct device *dev,
> - struct of_phandle_args *args)
> + struct of_phandle_args *args, struct fwnode_handle *fwnode)
> {
> const struct iommu_ops *ops = smmu->iommu.ops;
> int err;
>
> - err = iommu_fwspec_init(dev, &dev->of_node->fwnode, ops);
> + if (!fwnode)
> + return -ENOENT;
> +
> + err = iommu_fwspec_init(dev, fwnode, ops);
> if (err < 0) {
> dev_err(dev, "failed to initialize fwspec: %d\n", err);
> return err;
> @@ -835,6 +839,19 @@ static int tegra_smmu_configure(struct tegra_smmu *smmu, struct device *dev,
> return 0;
> }
>
> +static struct device_node *tegra_smmu_find_pci_np(struct pci_dev *pci_dev)
> +{
> + struct pci_bus *bus = pci_dev->bus;
> + struct device *dev = &bus->dev;
> +
> + while (!of_property_read_bool(dev->of_node, "iommus") && bus->parent) {
> + dev = &bus->parent->dev;
> + bus = bus->parent;
> + }
> +
> + return dev->of_node;
> +}

This seems like it's the equivalent of pci_get_host_bridge_device(). Can
you use that instead? I think you might use the parent of the host
bridge that's returned from that function, though.

Thierry
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