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

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Date:   Wed, 30 Sep 2020 18:26:30 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...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 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;
+}
+
 static struct iommu_device *tegra_smmu_probe_device(struct device *dev)
 {
 	struct device_node *np = dev->of_node;
@@ -843,11 +860,14 @@ static struct iommu_device *tegra_smmu_probe_device(struct device *dev)
 	unsigned int index = 0;
 	int err;
 
+	if (dev_is_pci(dev))
+		np = tegra_smmu_find_pci_np(to_pci_dev(dev));
+
 	while (of_parse_phandle_with_args(np, "iommus", "#iommu-cells", index,
 					  &args) == 0) {
 		smmu = tegra_smmu_find(args.np);
 		if (smmu) {
-			err = tegra_smmu_configure(smmu, dev, &args);
+			err = tegra_smmu_configure(smmu, dev, &args, &np->fwnode);
 			of_node_put(args.np);
 
 			if (err < 0)