ARM: OMAP2+: powerdomain: introduce logic for finding valid power domain

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 <j-pihet@ti.com>
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>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
diff --git a/arch/arm/mach-omap2/powerdomain.h b/arch/arm/mach-omap2/powerdomain.h
index a754c82..11bd4dd 100644
--- a/arch/arm/mach-omap2/powerdomain.h
+++ b/arch/arm/mach-omap2/powerdomain.h
@@ -220,6 +220,9 @@
 
 int pwrdm_get_mem_bank_count(struct powerdomain *pwrdm);
 
+u8 pwrdm_get_valid_lp_state(struct powerdomain *pwrdm,
+			    bool is_logic_state, u8 req_state);
+
 int pwrdm_set_next_pwrst(struct powerdomain *pwrdm, u8 pwrst);
 int pwrdm_read_next_pwrst(struct powerdomain *pwrdm);
 int pwrdm_read_pwrst(struct powerdomain *pwrdm);