[PATCH] clocksource: dw_apb_timer_of: return EPROBE_DEFER if no clock available

[Dinh Nguyen <dinguyen@kernel.org>]

commit ("b0fc70ce1f02 arm64: berlin: Select DW_APB_TIMER_OF") added the
support for the dw_apb_timer into the arm64 defconfig. However, for some
platforms like the Intel Stratix10 and Agilex, the clock manager doesn't
get probed until after the timer driver is probed. Thus, the driver hits
the panic "No clock nor clock-frequency property for %" because it cannot
properly get the clock.

This patch adds support for EPROBE_DEFER so the kernel can come back to
finish probing this timer driver after the clock driver is probed.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
---
 drivers/clocksource/dw_apb_timer_of.c | 86 ++++++++++++++++-----------
 1 file changed, 51 insertions(+), 35 deletions(-)

diff --git a/drivers/clocksource/dw_apb_timer_of.c b/drivers/clocksource/dw_apb_timer_of.c
index ab3ddebe8344..a8ce980c5146 100644
--- a/drivers/clocksource/dw_apb_timer_of.c
+++ b/drivers/clocksource/dw_apb_timer_of.c
@@ -14,7 +14,7 @@
 #include <linux/reset.h>
 #include <linux/sched_clock.h>
 
-static void __init timer_get_base_and_rate(struct device_node *np,
+static int __init timer_get_base_and_rate(struct device_node *np,
 				    void __iomem **base, u32 *rate)
 {
 	struct clk *timer_clk;
@@ -47,65 +47,77 @@ static void __init timer_get_base_and_rate(struct device_node *np,
 				np);
 
 	timer_clk = of_clk_get_by_name(np, "timer");
-	if (IS_ERR(timer_clk))
-		goto try_clock_freq;
+	if (IS_ERR(timer_clk)) {
+		if (PTR_ERR(timer_clk) != -EPROBE_DEFER) {
+			pr_err("Failed to get clock for %pOF\n", np);
+			goto try_clock_freq;
+		}
+		return PTR_ERR(timer_clk);
+	}
 
 	if (!clk_prepare_enable(timer_clk)) {
 		*rate = clk_get_rate(timer_clk);
-		return;
+		return 0;
 	}
 
 try_clock_freq:
 	if (of_property_read_u32(np, "clock-freq", rate) &&
 	    of_property_read_u32(np, "clock-frequency", rate))
 		panic("No clock nor clock-frequency property for %pOFn", np);
+	return 0;
 }
 
-static void __init add_clockevent(struct device_node *event_timer)
+static int __init add_clockevent(struct device_node *event_timer)
 {
 	void __iomem *iobase;
 	struct dw_apb_clock_event_device *ced;
 	u32 irq, rate;
+	int ret = 0;
 
 	irq = irq_of_parse_and_map(event_timer, 0);
 	if (irq == 0)
 		panic("No IRQ for clock event timer");
 
-	timer_get_base_and_rate(event_timer, &iobase, &rate);
-
-	ced = dw_apb_clockevent_init(-1, event_timer->name, 300, iobase, irq,
+	ret = timer_get_base_and_rate(event_timer, &iobase, &rate);
+	if (ret == 0) {
+		ced = dw_apb_clockevent_init(-1, event_timer->name, 300, iobase, irq,
 				     rate);
-	if (!ced)
-		panic("Unable to initialise clockevent device");
+		if (!ced)
+			panic("Unable to initialise clockevent device");
 
-	dw_apb_clockevent_register(ced);
+		dw_apb_clockevent_register(ced);
+	}
+	return ret;
 }
 
 static void __iomem *sched_io_base;
 static u32 sched_rate;
 
-static void __init add_clocksource(struct device_node *source_timer)
+static int __init add_clocksource(struct device_node *source_timer)
 {
 	void __iomem *iobase;
 	struct dw_apb_clocksource *cs;
 	u32 rate;
-
-	timer_get_base_and_rate(source_timer, &iobase, &rate);
-
-	cs = dw_apb_clocksource_init(300, source_timer->name, iobase, rate);
-	if (!cs)
-		panic("Unable to initialise clocksource device");
-
-	dw_apb_clocksource_start(cs);
-	dw_apb_clocksource_register(cs);
-
-	/*
-	 * Fallback to use the clocksource as sched_clock if no separate
-	 * timer is found. sched_io_base then points to the current_value
-	 * register of the clocksource timer.
-	 */
-	sched_io_base = iobase + 0x04;
-	sched_rate = rate;
+	int ret;
+
+	ret = timer_get_base_and_rate(source_timer, &iobase, &rate);
+	if (ret == 0) {
+		cs = dw_apb_clocksource_init(300, source_timer->name, iobase, rate);
+		if (!cs)
+			panic("Unable to initialise clocksource device");
+
+		dw_apb_clocksource_start(cs);
+		dw_apb_clocksource_register(cs);
+
+		/*
+		 * Fallback to use the clocksource as sched_clock if no separate
+		 * timer is found. sched_io_base then points to the current_value
+		 * register of the clocksource timer.
+		 */
+		sched_io_base = iobase + 0x04;
+		sched_rate = rate;
+	}
+	return ret;
 }
 
 static u64 notrace read_sched_clock(void)
@@ -146,25 +158,29 @@ static struct delay_timer dw_apb_delay_timer = {
 static int num_called;
 static int __init dw_apb_timer_init(struct device_node *timer)
 {
+	int ret = 0;
+
 	switch (num_called) {
 	case 1:
 		pr_debug("%s: found clocksource timer\n", __func__);
-		add_clocksource(timer);
-		init_sched_clock();
+		ret = add_clocksource(timer);
+		if (ret == 0) {
+			init_sched_clock();
 #ifdef CONFIG_ARM
-		dw_apb_delay_timer.freq = sched_rate;
-		register_current_timer_delay(&dw_apb_delay_timer);
+			dw_apb_delay_timer.freq = sched_rate;
+			register_current_timer_delay(&dw_apb_delay_timer);
 #endif
+		}
 		break;
 	default:
 		pr_debug("%s: found clockevent timer\n", __func__);
-		add_clockevent(timer);
+		ret = add_clockevent(timer);
 		break;
 	}
 
 	num_called++;
 
-	return 0;
+	return ret;
 }
 TIMER_OF_DECLARE(pc3x2_timer, "picochip,pc3x2-timer", dw_apb_timer_init);
 TIMER_OF_DECLARE(apb_timer_osc, "snps,dw-apb-timer-osc", dw_apb_timer_init);
-- 
2.17.1