Re: [PATCHv3 01/19] [HACK] of: dev_node has struct device pointer

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 10/25/2013 03:11 AM, Thierry Reding wrote:
...
> So my proposed solution for the IOMMU case is to treat it the same
> as any other resources. Perhaps resource isn't the right word, but
> at the core the issue is the same. A device requires the services
> of an IOMMU so that it can be put into the correct address space.
> If the IOMMU is not available yet it cannot do that, so we simply
> return -EPROBE_DEFER and cause the probe to be retried later.

Personally, I view deferred probe as being used when one device
requires either a resource /or/ a service provided by another, not
/just/ when there's a resource dependency. Hence, I think it fits
perfectly here.

So I agree with Thierry: In other words, I think the solution is for
all devices that are affected by an IOMMU to have a property such as:

iommu = <&iommu_phandle iommu_specifier>;

(and the DT node for the IOMMU will contain e.g. an #iommu-cells property)

... and for the driver to explicitly parse that property, and wait
until the driver for iommu_phandle is ready. Exactly the same as any
other resource/service dependency.

That will solve all the problems.

The only downside is that every driver needs to contain code to parse
that property. However, I think that's just one function call; the
actual implementation of that function can be unified somewhere inside
core code in drivers/iommu/.