bus: ti-sysc: Fix gpt12 system timer issue with reserved status

Jarkko Nikula <jarkko.nikula@bitmer.com> reported that Beagleboard
revision c2 stopped booting. Jarkko bisected the issue down to
commit 6cfcd556 ("clocksource/drivers/timer-ti-dm: Fix suspend
and resume for am3 and am4").

Let's fix the issue by tagging system timers as reserved rather than
ignoring them. And let's not probe any interconnect target module child
devices for reserved modules.

This allows PM runtime to keep track of clocks and clockdomains for
the interconnect target module, and prevent the system timer from idling
as we already have SYSC_QUIRK_NO_IDLE and SYSC_QUIRK_NO_IDLE_ON_INIT
flags set for system timers.

Fixes: 6cfcd556 ("clocksource/drivers/timer-ti-dm: Fix suspend and resume for am3 and am4")
Reported-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Tested-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/bus/ti-sysc.c

@@ -100,6 +100,7 @@ static const char * const clock_names[SYSC_MAX_CLOCKS] = {
  * @cookie: data used by legacy platform callbacks
  * @name: name if available
  * @revision: interconnect target module revision
+ * @reserved: target module is reserved and already in use
  * @enabled: sysc runtime enabled status
  * @needs_resume: runtime resume needed on resume from suspend
  * @child_needs_resume: runtime resume needed for child on resume from suspend
@@ -130,6 +131,7 @@ struct sysc {
 	struct ti_sysc_cookie cookie;
 	const char *name;
 	u32 revision;
+	unsigned int reserved:1;
 	unsigned int enabled:1;
 	unsigned int needs_resume:1;
 	unsigned int child_needs_resume:1;
@@ -3093,8 +3095,8 @@ static int sysc_probe(struct platform_device *pdev)
 		return error;
 
 	error = sysc_check_active_timer(ddata);
-	if (error)
-		return error;
+	if (error == -EBUSY)
+		ddata->reserved = true;
 
 	error = sysc_get_clocks(ddata);
 	if (error)
@@ -3130,11 +3132,15 @@ static int sysc_probe(struct platform_device *pdev)
 	sysc_show_registers(ddata);
 
 	ddata->dev->type = &sysc_device_type;
-	error = of_platform_populate(ddata->dev->of_node, sysc_match_table,
-				     pdata ? pdata->auxdata : NULL,
-				     ddata->dev);
-	if (error)
-		goto err;
+
+	if (!ddata->reserved) {
+		error = of_platform_populate(ddata->dev->of_node,
+					     sysc_match_table,
+					     pdata ? pdata->auxdata : NULL,
+					     ddata->dev);
+		if (error)
+			goto err;
+	}
 
 	INIT_DELAYED_WORK(&ddata->idle_work, ti_sysc_idle);