linux-kernel - Re: [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and .attach

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Message-ID: <20201001104245.GA3939583@ulmo>
Date:   Thu, 1 Oct 2020 12:42:45 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Dmitry Osipenko <digetx@...il.com>, joro@...tes.org,
        krzk@...nel.org, vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and
 .attach_dev

On Thu, Oct 01, 2020 at 03:33:19AM -0700, Nicolin Chen wrote:
> On Thu, Oct 01, 2020 at 11:51:52AM +0200, Thierry Reding 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.
> 
> > > @@ -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.
> 
> I noticed that one when looking up one of the of_ functions, yet
> also found that this pci_get_host_bridge_device() is privated by
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/pci/pci.h?id=975e1ac173058b8710e5979e97fc1397233301f3
> 
> Would PCI folks be that willing to (allow to) revert it?

Yeah, sounds like that would be useful. If you do, perhaps also take the
opportunity to replace open-coded variants, such as the one in arm-smmu.

Either that, or open-code this in tegra-smmu, like arm-smmu does.

Thierry

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