Hi Linus,

Am Montag, 22. August 2022, 10:38:11 CEST schrieb Linus Walleij:

On Tue, Aug 2, 2022 at 11:53 AM Quentin Schulz [off-list ref] wrote:

quoted

Some background on IO domains on Rockchip:

On some Rockchip SoCs, some SoC pins are split in what are called IO
domains.

An IO domain is supplied power externally, by regulators from a PMIC for
example. This external power supply is then used by the IO domain as
"supply" for the IO pins if they are outputs.

Each IO domain can configure which voltage the IO pins will be operating
on (1.8V or 3.3V).

There already exists an IO domain driver for Rockchip SoCs[1]. This
driver allows to explicit the relationship between the external power
supplies and IO domains[2]. This makes sure the regulators are enabled
by the Linux kernel so the IO domains are supplied with power and
correctly configured as per the supplied voltage.
This driver is a regulator consumer and does not offer any other
interface for device dependency.

What makes me confused about the patch is the relationship, if any,
between this "IO domain" and generic power domains (genpd) that has
been worked on for ~10 years.

I am worried that we are reinventing the world.

In a nutshell, the Rockchip io-domains handle the voltages of specific
pin-groups. I.e. mostly it is just switching between 1.8V and 3.3V .

The voltage itself is always set in a (i2c-)regulator but there is a
separate step necessary to tell the soc this information.

3.3 -> 1.8: set regulator to 1.8, tell io-domain "we're at 1.8 now"
1.8 -> 3.3: tell io-domain "3.3", set regulator to 3.3.

There is supposedly a soc-health-issue if you set the regulator to 3.3
while the io-domain thinks it's at 1.8 .


So the io-domain driver right now, just attaches to the regulator, catches
the voltage-change events and sets the io-domain setting accordingly.


What Quentin is trying to solve is a probe-dependency issue that can
happen when stuff is built into the kernel, the regulator has probed
the regulator using driver has probed, but the io.domain driver hasn't,
as that also only attached to the regulator as described above.

Heiko

While my intuitive feeling is that genpd power domains are only on-chip
and not considering off-chip pins, I am not so sure that it warrants
its own abstraction and want to know whether this can be retrofit into
genpd rather than inventing this?

Documentation/devicetree/bindings/power/power-domain.yaml
include/linux/pm_domain.h

Yours,
Linus Walleij

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