Nishanth Menon [off-list ref] writes:

powerdomain configuration in OMAP is done using PWRSTCTRL register for
each power domain. However, PRCM lets us write any value we'd like to
the logic and power domain target states, however the SoC integration
tends to actually function only at a few discrete states. These valid
states are already in our powerdomains_xxx_data.c file.

So, provide a function to easily query valid low power state that the
power domain is allowed to go to.

Based on work originally done by Jean Pihet [off-list ref]
https://patchwork.kernel.org/patch/1325091/ . There is no attempt to
create a new powerdomain solution here, except fixing issues seen
attempting invalid programming attempts. Future consolidation to the
generic powerdomain framework should consider this requirement as
well.

Similar solutions have been done in product kernels in the past such
as:
https://android.googlesource.com/kernel/omap.git/+blame/android-omap-panda-3.0/arch/arm/mach-omap2/pm44xx.c

Signed-off-by: Nishanth Menon <nm@ti.com>
---

nit: this is part of a fixes series, but it's more of a new feature.

That being said, the feature is needed and looks OK, except for...

+up_search:
+	/* OK, no deeper ones, can we get a higher match? */
+	new_pwrst = req_state + 1;
+	while (!(pwrdm_states & BIT(new_pwrst))) {
+		/* BUG if we have messed up database */
+		BUG_ON(new_pwrst > PWRDM_POWER_ON);

I don't think this is BUG() worthy, and should have a saner way to recover.

Kevin