[RFC] early init and DT platform devices allocation/registration

[Grant Likely]

On Fri, Jun 28, 2013 at 11:38 AM, Thierry Reding
<thierry.reding at gmail.com> wrote:
> On Fri, Jun 28, 2013 at 10:49:15AM +0200, Hiroshi Doyu wrote:
>> Grant Likely <grant.likely at secretlab.ca> wrote @ Wed, 26 Jun 2013 12:03:20 +0200:
>>
>> > On Wed, Jun 26, 2013 at 7:00 AM, Hiroshi Doyu <hdoyu at nvidia.com> wrote:
>> > > Grant Likely <grant.likely at secretlab.ca> wrote @ Tue, 25 Jun 2013 19:52:33 +0200:
>> > >
>> > >> > Here's my workaround. I need to call of_detach_node() with OF_DYNAMIC
>> > >> > to avoid duplicated device registration.
>> > >>
>> > >> Gah! my eyes!
>> > >>
>> > >> Don't do that. It is incredibly problematic. Look at inhibiting
>> > >> duplicate device creation instead.
>> > >
>> > > I may not follow this thread correctly, but could anyone point out the
>> > > above "inhibiting duplicate device creation" if there's already such
>> > > solution?
>> >
>> > No, the solution doesn't exist yet, but it wouldn't be hard to
>> > implement. What you need to do is to add a struct device pointer to
>> > struct device_node, and set the pointer to the struct device when
>> > of_platform_device_create creates a device. (it would also need to be
>> > set for early_platform_device creation, but that's not something that
>> > should affect you). You would also add a check to
>> > of_platform_device_create to check if the device pointer is already
>> > set. If it is, then skip creation of the device.
>>
>> Implemented as Grant suggested. At least this works for our case,
>> where IOMMU needs to be instanciated earlier than other device[1].
>> early_platform_device case still need to be covered.
>
> I think we arrived at a different conclusion in another branch of this
> thread. With the patch below every driver needs to explicitly allocate
> the platform device and set the struct device_node's .dev field, which
> has other side-effects such as the device hierarchy getting messed up.
>
> A better alternative would be to have of_platform_populate() run early
> such that the .dev field in the struct device_node can be set by core
> code, which would not require every driver to be changed.
>
> I'm not sure exactly what needs to be done to make this work, however.
> Grant, can you provide some guidance here as to how this may be fixed?
> Where would we have to call of_platform_populate() from and what makes
> this break with the current implementation?

Try it and see!  :-) I cannot give a definite answer, but I suspect
that it will fall down when registering the devices on to the
platform_bus because it isn't initialized yet. If called early, the
code would need to hold the platform_device in some kind of deferred
list until the platform bus was initialize, and then have a cleanup
function at initcall time to finish the registration of all early
devices.

g.