[PATCH 02/24] drivercore: Bind/unbind power domain on probe/remove

[Rafael J. Wysocki]

On Tuesday, June 10, 2014 02:53:26 PM Ulf Hansson wrote:
> On 10 June 2014 14:11, Rafael J. Wysocki <rafael at kernel.org> wrote:
> > On Tue, Jun 10, 2014 at 12:51 PM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
> >> From: Tomasz Figa <t.figa at samsung.com>
> >>
> >> On a number of platforms, devices are part of controllable power
> >> domains, which need to be enabled before such devices can be accessed
> >> and may be powered down when the device is idle to save some power.
> >> This means that on systems that support power domain control using
> >> generic power domains subsystem, it is necessary to add device to its
> >> power domain before binding a driver to it and remove it from its power
> >> domain after its driver is unbound to make sure that an unused device
> >> does not affect power domain state.
> >>
> >> Since this is not limited to particular busses and specific
> >> archs/platforms,
> >
> > Actually, this isn't correrct.  It is limited to the platforms that
> > use Device Trees now.
> 
> Correct, we should update the commit message/docs.
> 
> >
> > Moreover, it is not consistent with the way we add devices to the ACPI PM
> > domain, which is the ACPI counterpart of this.
> 
> I am not sure why you think consistency for ACPI is important here.
> ACPI PM will still be able to handle it's domain/device registering as
> before. There are even other pm_domains that don't use genpd which
> need to handle this themselves.

My point is that doing things like that in different places for different
firmware interfaces is confusing and likely to lead to coding mistakes in
the future.

> Or are you saying that you prefer bus notifiers in favour of making
> use of the driver core for this matter?

Well, please grep for acpi_dev_pm_attach() and see where it is done.
Surely not in drivers/base/dd.c.  Also I'm not sure why you're talking
about bus notifiers in this context.

> Shouldn't the driver core handle most of the common things for a device
> driver?

Common, yes.  Platform-specific, no.

> Let's compare how the pinctrls are being managed in the driver core, for
> example.

pinctrl has Device Trees support only at the moment (as far as firmware
interfaces go) and quite frankly I'm not sure if/how we'll need to change
it to cover ACPI as well.

But for power domains, please keep that stuff away from dd.c.  That is,
unless Greg specifically disagrees with me and decides to apply this
patch regardless. :-)

Rafael