Device probe order (i2c regulator vs. platform device)

[broonie@opensource.wolfsonmicro.com (Mark Brown)]

On Wed, Mar 24, 2010 at 08:10:38AM +0100, Marek Szyprowski wrote:

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> I've encountered a problem with regulator framework and the device
> probe order. In my system there is a pmic chip connected thought i2c bus
> and a platform device (let's call it A) that depends on the regulator
> device (for proper probing pmic chip must enable voltage to the device
> A). In the current configuration the i2c driver is also a platform
> device. However during the system initialization the device A is probed
> before the i2c driver would register pmic chip and its regulators.

This is (if I'm parsing what you say above correctly) a very common case
- if you look at most of the existing PMIC core and regulator drivers
you'll see that their initcalls are subsys_initcall(), and similarly for
the I2C controller drivers they use.  This means that at boot the PMICs
come up before pretty much any other device.

> How I can delay probing the device A to the moment when the regulator
> device will be available in the system? Is there any generic was of
> changing the device probe order?

The solution above is the other way around - it ensures that the
regulators come up first - but achieves the same effect.  Unfortunately
it's not as generic as would be best but it resolves the issues.