On Wed, Jun 10, 2015 at 12:19 PM, Tomeu Vizoso
[off-list ref] wrote:

On 10 June 2015 at 09:30, Linus Walleij [off-list ref] wrote:

quoted

regulator_get(...) -> not available, so:
- identify target regulator provider - this will need instrumentation
- probe it

It then turns out the regulator driver is on the i2c bus, so we
need to probe the i2c driver:
- identify target i2c host for the regulator driver - this will need
  instrumentation
- probe the i2c host driver

i2c host comes out, probes the regulator driver, regulator driver
probes and then the regulator_get() call returns.

Hmm, if I understand correctly what you say, this is exactly what this
particular series does:

regulator_get -> of_platform_device_ensure -> probe() on the platform
device that encloses the requested device node (i2c host) -> i2c slave
gets probed and the regulator registered -> regulator_get returns the
requested resource

Yes. But only for device tree.

The downside I'm currently looking at is that an explicit dependency
graph would be useful to have for other purposes. For example to print
a neat warning when a dependency cannot be fulfilled. Or to refuse to
unbind a device which other devices depend on, or to automatically
unbind the devices that depend on it, or to print a warning if a
device is hotplugged off and other devices depend on it.

Unbind/remove() calls are the inverse usually yes.

But also the [runtime] power up/down sequences for the
devices tend to depend on a similar ordering or mostly
the same. (Mentioned this before I think.)

quoted

This requires instrumentation on anything providing a resource
to another driver like those I mentioned and a lot of overhead
infrastructure, but I think it's the right approach. However I don't
know if I would ever be able to pull that off myself, I know talk
is cheap and I should show the code instead.

Yeah, if you can give it a second look and say if it matches what you
wrote above, it would be very much appreciated.

Yes you are right. But what about ACPI, board files,
Simple Firmware and future hardware description languages...

Yours,
Linus Walleij