[RFC PATCH 3/4] rtc: rzn1: support input frequencies other than 32768Hz

[Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>]

When using the SCMP mode instead of SUBU, this RTC can also support
other input frequencies than 32768Hz. Also, upcoming SoCs will only
support SCMP.

Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
 drivers/rtc/rtc-rzn1.c | 43 ++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index e3733534d409..f8c9308817ae 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/bcd.h>
+#include <linux/clk.h>
 #include <linux/init.h>
 #include <linux/iopoll.h>
 #include <linux/module.h>
@@ -22,7 +23,6 @@
 #include <linux/spinlock.h>
 
 #define RZN1_RTC_CTL0 0x00
-#define   RZN1_RTC_CTL0_SLSB_SUBU 0
 #define   RZN1_RTC_CTL0_SLSB_SCMP BIT(4)
 #define   RZN1_RTC_CTL0_AMPM BIT(5)
 #define   RZN1_RTC_CTL0_CE BIT(7)
@@ -49,6 +49,8 @@
 #define   RZN1_RTC_SUBU_DEV BIT(7)
 #define   RZN1_RTC_SUBU_DECR BIT(6)
 
+#define RZN1_RTC_SCMP 0x3c
+
 #define RZN1_RTC_ALM 0x40
 #define RZN1_RTC_ALH 0x44
 #define RZN1_RTC_ALW 0x48
@@ -356,19 +358,20 @@ static int rzn1_rtc_set_offset(struct device *dev, long offset)
 	return 0;
 }
 
-static const struct rtc_class_ops rzn1_rtc_ops = {
+static struct rtc_class_ops rzn1_rtc_ops = {
 	.read_time = rzn1_rtc_read_time,
 	.set_time = rzn1_rtc_set_time,
 	.read_alarm = rzn1_rtc_read_alarm,
 	.set_alarm = rzn1_rtc_set_alarm,
 	.alarm_irq_enable = rzn1_rtc_alarm_irq_enable,
-	.read_offset = rzn1_rtc_read_offset,
-	.set_offset = rzn1_rtc_set_offset,
 };
 
 static int rzn1_rtc_probe(struct platform_device *pdev)
 {
 	struct rzn1_rtc *rtc;
+	struct clk *xtal;
+	unsigned long rate;
+	u32 use_scmp = 0;
 	int irq;
 	int ret;
 
@@ -402,12 +405,32 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
-	/*
-	 * Ensure the clock counter is enabled.
-	 * Set 24-hour mode and possible oscillator offset compensation in SUBU mode.
-	 */
-	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | RZN1_RTC_CTL0_SLSB_SUBU,
-	       rtc->base + RZN1_RTC_CTL0);
+	/* Only switch to scmp if we have an xtal clock with a valid rate and != 32768 */
+	xtal = devm_clk_get_optional(&pdev->dev, "xtal");
+	if (IS_ERR(xtal)) {
+		ret = PTR_ERR(xtal);
+		goto dis_runtime_pm;
+	} else if (xtal) {
+		rate = clk_get_rate(xtal);
+
+		if (rate < 32000 || rate > BIT(22)) {
+			ret = -EOPNOTSUPP;
+			goto dis_runtime_pm;
+		}
+
+		if (rate != 32768)
+			use_scmp = RZN1_RTC_CTL0_SLSB_SCMP;
+	}
+
+	if (use_scmp) {
+		writel(rate - 1, rtc->base + RZN1_RTC_SCMP);
+	} else {
+		rzn1_rtc_ops.read_offset = rzn1_rtc_read_offset;
+		rzn1_rtc_ops.set_offset = rzn1_rtc_set_offset;
+	}
+
+	/* Ensure clock counter is enabled. Set 24-hour mode and SUBU or SCMP mode */
+	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | use_scmp, rtc->base + RZN1_RTC_CTL0);
 
 	/* Disable all interrupts */
 	writel(0, rtc->base + RZN1_RTC_CTL1);
-- 
2.47.2