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regulator: bd9571mwv: Document "backup_mode" sysfs file

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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>
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Geert Uytterhoeven 2018-07-16 17:30:52 +02:00 committed by Mark Brown
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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.