[PATCH v4 2/8] timer: Add helper for drivers using timebase fallback

[Sean Anderson <seanga2@gmail.com>]

This function is designed to be used when a timer used to be initialized by
the cpu (e.g. RISC-V timers), but now is initialized by dm_timer_init. In
such a case, the timer may prefer to use the clocks and clock-frequency
properties, but should be able to fall back on using the cpu's
timebase-frequency.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
---

Changes in v4:
- New

 drivers/timer/timer-uclass.c | 25 +++++++++++++++++++++++++
 include/timer.h              | 15 +++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/timer/timer-uclass.c b/drivers/timer/timer-uclass.c
index 14dde950a1..fb2f4c351a 100644
--- a/drivers/timer/timer-uclass.c
+++ b/drivers/timer/timer-uclass.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <cpu.h>
 #include <dm.h>
 #include <init.h>
 #include <dm/lists.h>
@@ -79,6 +80,30 @@ static int timer_post_probe(struct udevice *dev)
 	return 0;
 }
 
+int timer_timebase_fallback(struct udevice *dev)
+{
+	struct udevice *cpu;
+	struct cpu_platdata *cpu_plat;
+	struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
+
+	/* Did we get our clock rate from the device tree? */
+	if (uc_priv->clock_rate)
+		return 0;
+
+	/* Fall back to timebase-frequency */
+	dev_dbg(dev, "missing clocks or clock-frequency property; falling back on timebase-frequency\n");
+	cpu = cpu_get_current_dev();
+	if (!cpu)
+		return -ENODEV;
+
+	cpu_plat = dev_get_parent_platdata(cpu);
+	if (!cpu_plat)
+		return -ENODEV;
+
+	uc_priv->clock_rate = cpu_plat->timebase_freq;
+	return 0;
+}
+
 u64 timer_conv_64(u32 count)
 {
 	/* increment tbh if tbl has rolled over */
diff --git a/include/timer.h b/include/timer.h
index a49b500ce3..8b9fa51c53 100644
--- a/include/timer.h
+++ b/include/timer.h
@@ -15,6 +15,21 @@
  */
 int dm_timer_init(void);
 
+/**
+ * timer_timebase_fallback() - Helper for timers using timebase fallback
+ * @dev: A timer partially-probed timer device
+ *
+ * This is a helper function designed for timers which need to fall back on the
+ * cpu's timebase. This function is designed to be called during the driver's
+ * probe(). If there is a clocks or clock-frequency property in the timer's
+ * binding, then it will be used. Otherwise, the timebase of the current cpu
+ * will be used. This is initialized by the cpu driver, and usually gotten from
+ * ``/cpus/timebase-frequency`` or ``/cpus/cpu at X/timebase-frequency``.
+ *
+ * Return: 0 if OK, or negative error code on failure
+ */
+int timer_timebase_fallback(struct udevice *dev);
+
 /*
  * timer_conv_64 - convert 32-bit counter value to 64-bit
  *
-- 
2.28.0