regulator: bd9571mwv: Document "backup_mode" sysfs file

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator b/Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator
new file mode 100644 (file)
index 0000000..4d63a79
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator
@@ -0,0 +1,27 @@
+What:          /sys/bus/i2c/devices/.../bd9571mwv-regulator.*.auto/backup_mode
+Date:          Jul 2018
+KernelVersion: 4.19
+Contact:       Geert Uytterhoeven <geert+renesas@glider.be>
+Description:   Read/write the current state of DDR Backup Mode, which controls
+               if DDR power rails will be kept powered during system suspend.
+               ("on"/"1" = enabled, "off"/"0" = disabled).
+               Two types of power switches (or control signals) can be used:
+                 A. With a momentary power switch (or pulse signal), DDR
+                    Backup Mode is enabled by default when available, as the
+                    PMIC will be configured only during system suspend.
+                 B. With a toggle power switch (or level signal), the
+                    following steps must be followed exactly:
+                      1. Configure PMIC for backup mode, to change the role of
+                         the accessory power switch from a power switch to a
+                         wake-up switch,
+                      2. Switch accessory power switch off, to prepare for
+                         system suspend, which is a manual step not controlled
+                         by software,
+                      3. Suspend system,
+                      4. Switch accessory power switch on, to resume the
+                         system.
+                    DDR Backup Mode must be explicitly enabled by the user,
+                    to invoke step 1.
+               See also Documentation/devicetree/bindings/mfd/bd9571mwv.txt.
+Users:         User space applications for embedded boards equipped with a
+               BD9571MWV PMIC.