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Re: [PATCH v3 02/18] of/platform: add of_platform_probe

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On 7 August 2015 at 14:19, Mark Brown <broonie@kernel.org> wrote:
> On Thu, Aug 06, 2015 at 04:11:39PM +0200, Tomeu Vizoso wrote:
>
>> Walks the OF tree up and finds the closest ancestor that has a platform
>> device associated with it, probing it if isn't bound to a driver yet.
>
>> The above should ensure that the dependency represented by the passed OF
>> node is available, because probing a platform device should cause its
>> descendants to be probed as well.
>
> This sounds like it's going to break in the case where we have MFDs that
> represent their functions in DT (not a pattern I'm a fan of but it's a
> thing people do).  We'll walk back to the platform device for the MFD
> function, try to probe it and then give up.  Perhaps that's good enough
> anyway but it's not clear to me why we don't just try every parent we
> find?

Agreed. In the attempt at probing dependencies before a device is
probed, I considered that a device's parent is also a dependency and
that worked well. From what I saw, few devices will defer their probe
if their parent hasn't been probed yet, assuming that it will have
probed already. But with simple-mfd and simple-bus that shouldn't be
relied upon as things will break if their parents defer their probe.
With async probing enabled this failure scenario becomes more
probable.

> I'm also not a fan of the fact that the interface here is explicitly
> saying that we want to probe a platform device, that's an implementation
> detail that callers shouldn't need to know about.  From the point of
> view of the callers what they're trying to do is kick any dependencies
> into being instantiated, the fact that we currently try to accomplish it
> with platform devices isn't something they care about.

Agreed.

Thanks,

Tomeu
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[PATCH v3 0/18] On-demand device probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-06 16:30 +0200
  [PATCH v3 02/18] of/platform: add of_platform_probe Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-06 16:30 +0200
    Re: [PATCH v3 02/18] of/platform: add of_platform_probe Mark Brown <broonie@kernel.org> - 2015-08-07 14:20 +0200
      Re: [PATCH v3 02/18] of/platform: add of_platform_probe Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-11 11:40 +0200
  [PATCH v3 05/18] regulator: core: Reduce critical area in _regulator_get Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-06 16:30 +0200
    Re: [PATCH v3 05/18] regulator: core: Reduce critical area in  _regulator_get Mark Brown <broonie@kernel.org> - 2015-08-07 14:10 +0200
  [PATCH v3 01/18] platform: delay OF device-driver matches until late_initcall Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-06 16:30 +0200
    Re: [PATCH v3 01/18] platform: delay OF device-driver matches until late_initcall Rob Herring <robherring2@gmail.com> - 2015-08-06 22:20 +0200
      Re: [PATCH v3 01/18] platform: delay OF device-driver matches until late_initcall Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-07 09:20 +0200
        Re: [PATCH v3 01/18] platform: delay OF device-driver matches until  late_initcall Grygorii Strashko <grygorii.strashko@ti.com> - 2015-08-07 19:10 +0200
          Re: [PATCH v3 01/18] platform: delay OF device-driver matches until late_initcall Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-09 15:10 +0200
            Re: [PATCH v3 01/18] platform: delay OF device-driver matches until  late_initcall Mark Brown <broonie@kernel.org> - 2015-08-10 12:30 +0200
            Re: [PATCH v3 01/18] platform: delay OF device-driver matches until  late_initcall Grygorii Strashko <grygorii.strashko@ti.com> - 2015-08-14 21:20 +0200
  Re: [PATCH v3 0/18] On-demand device probing Rob Herring <robherring2@gmail.com> - 2015-08-06 22:20 +0200
    Re: [PATCH v3 0/18] On-demand device probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2015-08-07 09:00 +0200

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