[PATCHv5 2/9] driver/core: populate devices in order for IOMMUs

[Hiroshi Doyu]

Stephen Warren <swarren at wwwdotorg.org> wrote @ Tue, 19 Nov 2013 22:22:47 +0100:

> On 11/19/2013 05:03 AM, Hiroshi Doyu wrote:
> > Hi Thierry,
> > 
> > Thierry Reding <thierry.reding at gmail.com> wrote @ Tue, 19 Nov 2013 11:25:07 +0100:
> > 
> >> From earlier discussions I thought the goal was to actually defer this
> >> until all nodes referred to by the iommus property were actually
> >> registered. The above only checks that the phandles can be resolved to
> >> valid struct device_node:s. That doesn't mean that an actual IOMMU has
> >> been registered for it, only that the devices have been created.
> > 
> > Currently "bus->iommu_ops" is set at the end of tegra_smmu_probe(). So
> > if "bus->iommu_ops" is set, it means that an iommu instance is
> > populated at that time.
> 
> Yes, but that's the register bus, upon which the device is a client, not
> the bus upon which the device is a bus master. They aren't necessarily
> the same.
> 
> There's no getting around the fact that, as Thierry said, you need to
> search for a registered IOMMU device for each phandle, and defer probe
> if any aren't registered yet.
> 
> If we do that, then you shouldn't need to look at the value of
> dev->bus->iommu_ops at all; if all IOMMUs in the list were registered,
> then iommu_ops must have been set when (one of them) was registered, and
> if not, then it possibly wasn't, so defer probe.
> 
> That way, this code won't have to change if the core IOMMU code gets
> extended to support multiple IOMMUs, devices mastering transactions onto
> buses other than their register bus, etc.

Does the above mean the following?

int of_iommu_attach(struct device *dev)
{
	int i;
	struct of_phandle_args args;

	of_property_for_each_phandle_with_args(dev->of_node, "iommus",
					       "#iommu-cells", i, &args)
		if (!args->np->dev->driver)
			return -EPROBE_DEFER;
	return 0;
}


"args->np->dev->driver" needs the following patch:

  http://lists.linuxfoundation.org/pipermail/iommu/2013-July/006023.html