On Thu, 24 Oct 2013 11:21:15 +0200, Hiroshi Doyu <hdoyu@xxxxxxxxxx> wrote:
> Hi Grant,
>
> Grant Likely <grant.likely@xxxxxxxxxx> wrote @ Thu, 24 Oct 2013 10:55:31 +0200:
> ....
> > > diff --git a/include/linux/of.h b/include/linux/of.h
> > > index f95aee3..638a88a 100644
> > > --- a/include/linux/of.h
> > > +++ b/include/linux/of.h
> > > @@ -60,6 +60,7 @@ struct device_node {
> > > struct kref kref;
> > > unsigned long _flags;
> > > void *data;
> > > + struct device *dev; /* Set only after populated */
> >
> > Is this being used merely to indicate that a device has been processed
> > by of_platform_device_create()? Or do you intend to dereference this
> > pointer? I've avoided putting the struct device in to the device_node
> > structure up to this point simply becuase there aren't any good clues
> > for what /kind/ of device it actually points to. I worry that bad
> > assumptions will get made when other subsystems try to use the
> > same pointer. ie. if one subsystem creates its own device and sets this
> > pointer, and then of_platform_device_create() comes along behind, sees
> > that it is already created, and then returns a platform_device pointer
> > *for something that isn't a struct platform_device*. This is very bad.
> >
> > Instead of using a pointer to the struct device, would a flag be
> > sufficient for your purposes? Would it be fine to return NULL if the
> > device has already been created?
>
> Yes, a flag would be enough for this purpose.
>
> This patch is a part of HACK to control device instanciation order. We
> have an IOMMU device(platform) which needs to be instanciated earlier
> than other (platform)devices so that IOMMU driver would configure them
> as IOMMU'able device.
Ideally the drivers depending on the IOMMU would return -EPROBE_DEFER if
the IOMMU driver isn't set up so that you don't need to play games with
probe order. Creating certain platform devices early is a really ugly
and fragile solution.
Besides, probe order of device drivers is far more about link order of
the kernel than it is about when of_platform_device_create() is called.
Fiddling with the initcall level on the IOMMU driver (while not
recommended) may very well have the effect you desire.
g.
>
> Is there any better way to control device instanciation order from DT?
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