ARM: OMAP4: Fix legacy code clean-up regression

Commit 2a26d31b ("ARM: OMAP2+: Remove unused legacy code for PRM")
removed PRM platform init code that I thought is unused. Turns out omap4
still needs this code, so let's do a partial revert to add it back.

I probably missed this earlier as the comments used to say
"OMAP4+ is DT only now" for !of_have_populated_dt() to exit early and
missed the negative test. Let's not add those lines back as they are
confusing and no longer needed as we only boot in device tree mode.

Without things things can mysterious fail for i2c, for example LM75
I2C temperature sensor can stop working as the PRM interrupts won't work.

Fixes: 2a26d31b ("ARM: OMAP2+: Remove unused legacy code for PRM")
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/prm44xx.c

@@ -336,6 +336,27 @@ static void omap44xx_prm_reconfigure_io_chain(void)
 	return;
 }
 
+/**
+ * omap44xx_prm_enable_io_wakeup - enable wakeup events from I/O wakeup latches
+ *
+ * Activates the I/O wakeup event latches and allows events logged by
+ * those latches to signal a wakeup event to the PRCM.  For I/O wakeups
+ * to occur, WAKEUPENABLE bits must be set in the pad mux registers, and
+ * omap44xx_prm_reconfigure_io_chain() must be called.  No return value.
+ */
+static void __init omap44xx_prm_enable_io_wakeup(void)
+{
+	s32 inst = omap4_prmst_get_prm_dev_inst();
+
+	if (inst == PRM_INSTANCE_UNKNOWN)
+		return;
+
+	omap4_prm_rmw_inst_reg_bits(OMAP4430_GLOBAL_WUEN_MASK,
+				    OMAP4430_GLOBAL_WUEN_MASK,
+				    inst,
+				    omap4_prcm_irq_setup.pm_ctrl);
+}
+
 /**
  * omap44xx_prm_read_reset_sources - return the last SoC reset source
  *
@@ -668,6 +689,8 @@ struct pwrdm_ops omap4_pwrdm_operations = {
 	.pwrdm_has_voltdm	= omap4_check_vcvp,
 };
 
+static int omap44xx_prm_late_init(void);
+
 /*
  * XXX document
  */
@@ -675,6 +698,7 @@ static struct prm_ll_data omap44xx_prm_ll_data = {
 	.read_reset_sources = &omap44xx_prm_read_reset_sources,
 	.was_any_context_lost_old = &omap44xx_prm_was_any_context_lost_old,
 	.clear_context_loss_flags_old = &omap44xx_prm_clear_context_loss_flags_old,
+	.late_init = &omap44xx_prm_late_init,
 	.assert_hardreset	= omap4_prminst_assert_hardreset,
 	.deassert_hardreset	= omap4_prminst_deassert_hardreset,
 	.is_hardreset_asserted	= omap4_prminst_is_hardreset_asserted,
@@ -711,6 +735,37 @@ int __init omap44xx_prm_init(const struct omap_prcm_init_data *data)
 	return prm_register(&omap44xx_prm_ll_data);
 }
 
+static int omap44xx_prm_late_init(void)
+{
+	int irq_num;
+
+	if (!(prm_features & PRM_HAS_IO_WAKEUP))
+		return 0;
+
+	irq_num = of_irq_get(prm_init_data->np, 0);
+	/*
+	 * Already have OMAP4 IRQ num. For all other platforms, we need
+	 * IRQ numbers from DT
+	 */
+	if (irq_num < 0 && !(prm_init_data->flags & PRM_IRQ_DEFAULT)) {
+		if (irq_num == -EPROBE_DEFER)
+			return irq_num;
+
+		/* Have nothing to do */
+		return 0;
+	}
+
+	/* Once OMAP4 DT is filled as well */
+	if (irq_num >= 0) {
+		omap4_prcm_irq_setup.irq = irq_num;
+		omap4_prcm_irq_setup.xlate_irq = NULL;
+	}
+
+	omap44xx_prm_enable_io_wakeup();
+
+	return omap_prcm_register_chain_handler(&omap4_prcm_irq_setup);
+}
+
 static void __exit omap44xx_prm_exit(void)
 {
 	prm_unregister(&omap44xx_prm_ll_data);