[RFC][PATCH] rtc: sunxi: use external 32k oscillator if provided

[Mans Rullgard <mans@mansr.com>]

Set the OSC32K_SRC_SEL bit in the LOSC control register if a clock is
specified in the devicetree.

Signed-off-by: Mans Rullgard <mans@mansr.com>
---
The newer sun6i rtc driver is a proper clk provider with parent
selection.  Doing the same thing in this driver would be difficult
while staying compatible with existing devicetrees.  For that reason,
this simpler approach seems reasonable.
---
 drivers/rtc/rtc-sunxi.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/rtc/rtc-sunxi.c b/drivers/rtc/rtc-sunxi.c
index 5d019e3a835a..4f1053eab778 100644
--- a/drivers/rtc/rtc-sunxi.c
+++ b/drivers/rtc/rtc-sunxi.c
@@ -5,6 +5,7 @@
  * Copyright (c) 2013, Carlo Caione <carlo.caione@gmail.com>
  */
 
+#include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/fs.h>
@@ -21,8 +22,10 @@
 #include <linux/types.h>
 
 #define SUNXI_LOSC_CTRL				0x0000
+#define SUNXI_LOSC_CTRL_KEY			(0x16aa << 16)
 #define SUNXI_LOSC_CTRL_RTC_HMS_ACC		BIT(8)
 #define SUNXI_LOSC_CTRL_RTC_YMD_ACC		BIT(7)
+#define SUNXI_LOSC_CTRL_OSC32K_SRC_SEL		BIT(0)
 
 #define SUNXI_RTC_YMD				0x0004
 
@@ -422,6 +425,7 @@ MODULE_DEVICE_TABLE(of, sunxi_rtc_dt_ids);
 static int sunxi_rtc_probe(struct platform_device *pdev)
 {
 	struct sunxi_rtc_dev *chip;
+	struct clk *extclk;
 	int ret;
 
 	chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
@@ -455,6 +459,14 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
 		return -ENODEV;
 	}
 
+	/* use external oscillator if present */
+	extclk = devm_clk_get_optional_enabled(&pdev->dev, NULL);
+	if (IS_ERR(extclk))
+		return PTR_ERR(extclk);
+	if (extclk)
+		writel(SUNXI_LOSC_CTRL_KEY | SUNXI_LOSC_CTRL_OSC32K_SRC_SEL,
+		       chip->base + SUNXI_LOSC_CTRL);
+
 	/* clear the alarm count value */
 	writel(0, chip->base + SUNXI_ALRM_DHMS);
 
-- 
2.41.0