PENDING: fix(psci): prepare SCR state and barriers around WFI

Executing WFI at EL3 without explicitly configuring scr_el3
leads to unstable behaviour and systems hangs on entering
the low power mode.

Save and update scr_el3 with required bits for routing of
interrupts and restoring original scr_el3 value on resume to
ensure correct entry and exit from WFI.

Signed-off-by: Scaria Kochidanadu <s-kochidanadu@ti.com>

Author: ti-scaria

lib/psci/psci_suspend.c

@@ -255,7 +255,14 @@ int psci_cpu_suspend_start(unsigned int idx,
 	 * requested at multiple power levels. This means that the cpu
 	 * context will be preserved.
 	 */
+
+	u_register_t scr;
+	scr = read_scr_el3();
+	write_scr_el3(scr | SCR_IRQ_BIT | SCR_FIQ_BIT);
+	isb();
+	dsb();
 	wfi();
+	write_scr_el3(scr);
 
 #if ENABLE_RUNTIME_INSTRUMENTATION
 	PMF_CAPTURE_TIMESTAMP(rt_instr_svc,