[PATCH] rtc: pcf85063: disable the clkout output by default

["A. Sverdlin" <alexander.sverdlin@siemens.com>]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

The PCF85063 powers up with its CLKOUT pin driving the 32.768 kHz. While
it's possible to request a specific default frequency in the DT via
assigned-clocks/assigned-clock-rates on the RTC node itself, even without
a real consumer referencing the clock, there is no such possibility to
disable the clock output by default.

Therefore gate CLKOUT in the driver before registering the OF provider,
mirroring the pcf8563 and hym8563 siblings which already force an off state
at registration. Doing it before devm_of_clk_add_hw_provider() leaves the
real consumers in the device tree free to re-enable the output afterwards,
while an otherwise unused CLKOUT now stays off.

In practice it means that with CLKOUT disabled the RTC consumes around
250nA at 25°C and 6-10uA with CLKOUT enabled (5v Vdd). Which means days vs
hours on a supercapacitor.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
 drivers/rtc/rtc-pcf85063.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c
index 01e209d88f5f3..0b6d8083b6456 100644
--- a/drivers/rtc/rtc-pcf85063.c
+++ b/drivers/rtc/rtc-pcf85063.c
@@ -523,6 +523,12 @@ static struct clk *pcf85063_clkout_register_clk(struct pcf85063 *pcf85063)
 	/* optional override of the clockname */
 	of_property_read_string(node, "clock-output-names", &init.name);
 
+	/* power-on default is the 32768 Hz output on; gate it until claimed */
+	ret = regmap_update_bits(pcf85063->regmap, PCF85063_REG_CTRL2,
+				 PCF85063_REG_CLKO_F_MASK, PCF85063_REG_CLKO_F_OFF);
+	if (ret)
+		return ret;
+
 	/* register the clock */
 	clk = devm_clk_register(&pcf85063->rtc->dev, &pcf85063->clkout_hw);
 
-- 
2.55.0