Document the "subordinate" sysfs attribute exposed by the PEF2256
driver.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 .../ABI/testing/sysfs-bus-platform-devices-pef2256   | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-platform-devices-pef2256

diff --git a/Documentation/ABI/testing/sysfs-bus-platform-devices-pef2256 b/Documentation/ABI/testing/sysfs-bus-platform-devices-pef2256
new file mode 100644
index 000000000000..95ba1ae55daf
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-platform-devices-pef2256
@@ -0,0 +1,12 @@
+What:		/sys/bus/platform/devices/*.pef2256/subordinate
+KernelVersion:	6.4
+Contact:	Herve Codina <herve.codina@bootlin.com>
+Description:
+		(RW) Controls whether the PEF2256 works as subordinate or main
+		device mode.
+
+		- 0: main device mode
+		- 1: subordinate mode
+
+		In subordinate device mode it synchronizes on line interface
+		clock signals. Otherwise, it synchronizes on internal clocks.
-- 
2.39.2