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>

1 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator b/Documentation/ABI/testing/sysfs-driver-bd9571mwv-regulator
new file mode 100644
index 000000000000..4d63a7904b94
--- /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.