Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider which controls

[Francesco Dolcini <francesco.dolcini@toradex.com>]

Hello Ulf and everybody,

On Wed, Jul 13, 2022 at 01:43:28PM +0200, Ulf Hansson wrote:
> On Thu, 23 Jun 2022 at 18:14, Max Krummenacher <max.oss.09@gmail.com> wrote:
> > So our plan is to explicitly handle a (shared) regulator in every
> > driver involved, adding that regulator capability for drivers not
> > already having one.
> 
> Please don't! I have recently rejected a similar approach for Tegra
> platforms, which now have been converted into using the power domain
> approach.

Just to quickly re-iterate how our hardware design looks like, we do
have a single gpio that control the power of a whole board area that is
supposed to be powered-off in suspend mode, this area could contains
devices that have a proper Linux driver and some passive driver-less
components (e.g. level shifter) - the exact mix varies.

Our proposal in this series was to model this as a power domain that
could be controlled with a regulator. Krzysztof, Robin and others
clearly argued against this idea.

The other approach would be to have a single regulator shared with the
multiple devices we have there (still not clear how that would work in
case we have only driver-less passive components). This is just a
device-tree matter, maybe we would need to add support for a supply to
some device drivers.

Honestly my conclusion from this discussion is that the only viable
option is this second one, do I miss something?

> If it's a powerail that is shared between controllers (devices), used
> to keep their registers values for example, that should be modelled as
> a power domain. Moreover for power domains, we can support
> voltage/frequency (performance) scaling, which isn't really applicable
> to a plain regulator.
> 
> However, if the actual powerrail fits well to be modelled as
> regulator, please go ahead. Although, in this case, the regulator must
> only be controlled behind a genpd provider's on/off callback, so you
> still need the power domain approach, rather than using the regulator
> in each driver and for each device.

Francesco