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

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Thu, Oct 31, 2013 at 10:37:40AM -0600, Stephen Warren wrote:
> On 10/31/2013 02:14 AM, Hiroshi Doyu wrote:
> > Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote @ Wed, 30 Oct 2013 23:41:09 +0100:
> > 
> >> My earlier proposal for deferred interrupt reference resolution actually
> >> tries to solve that problem within the core. Essentially what it does is
> >> add a new function that gets called right before the driver's .probe()
> >> function, so that it can parse standard resources and services from DT,
> >> such as the interrupts property. This could theoretically be done for
> >> other resources such as reg as well, but it really only matters where
> >> the resource can be dynamic (as is the case for interrupts).
> >>
> >> In this case I would envision a standard OF function to associate a
> >> device with its IOMMU. Perhaps something like:
> >>
> >> 	int of_iommu_attach(struct device *dev);
> >>
> >> That could be called by the core independent of the specific device and
> >> IOMMU. IOMMU-specifics can probably be handled using .of_xlate(), quite
> >> in a similar way to GPIO or regulators.
> >>
> >> That way drivers can remain agnostic of the IOMMU while still being able
> >> to take advantage of deferred probing.
> > 
> > This could be simpler than making "bus_notifier" return "-EPROBE_DEFER".
> > 
> > The disadvantage of this is that we may need to provide the similar
> > of_<"subsystem">_attach() per subsytem if needed.
> 
> Well, "per subsystem" here means per subsystem that is providing
> resources, not per subsystem that is consuming resources. How many
> subsystems are you expecting to provide resources like this? At present,
> I believe IOMMU is the only subsystem missing some kind of API for
> clients to acquire the relevant resource. I don't think there's any
> scalability problem here.

Furthermore if the subsystem wants to provide resources then it needs
such a function anyway, so there really isn't any overhead here.

Thierry

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