linux-kernel - Re: [PATCHv5 2/9] driver/core: populate devices in order for IOMMUs

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Date:	Wed, 20 Nov 2013 04:17:08 +0100
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"swarren@...dotorg.org" <swarren@...dotorg.org>
CC:	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	Stephen Warren <swarren@...dia.com>,
	"will.deacon@....com" <will.deacon@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 2/9] driver/core: populate devices in order for IOMMUs

Stephen Warren <swarren@...dotorg.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@...il.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
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