dt-binding: pcf8523: add xtal load capacitance

The NXP pcf8523 supports two different xtal load capacitance
- 7000fF  (7pF)    HW default
- 12500fF (12.5pF) Minimum power consumption, driver default

To obtain a precise RTC the pcf8523 must be configured
with the correct capacitance load of the xtal.

Add a property to specify the xtal capacitance load.
The default value matches that of the current Linux driver.

With a dedicated binding remove the entry in rtc.txt

Signed-off-by: Søren Andersen <san@skov.dk>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
new file mode 100644
index 000000000000..0b1080c60f63
--- /dev/null
+++ b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
@@ -0,0 +1,18 @@
+* NXP PCF8523 Real Time Clock
+
+Required properties:
+- compatible: Should contain "nxp,pcf8523".
+- reg: I2C address for chip.
+
+Optional property:
+- quartz-load-femtofarads: The capacitive load of the quartz(x-tal),
+  expressed in femto Farad (fF). Valid values are 7000 and 12500.
+  Default value (if no value is specified) is 12500fF.
+
+Example:
+
+pcf8523: rtc@68 {
+	compatible = "nxp,pcf8523";
+	reg = <0x68>;
+	quartz-load-femtofarads = <7000>;
+};