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regulator: BD71847 support commonly used feedback connection 

The BD71847 buck output voltages are in a few cases scaled using external
connection which adds a pull-up to regulator feedback pin. This connection
will adjust output voltage from regulator in a deterministic way.

Add support for describing this HW connection so that driver can adjust
voltage ranges accordingly.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/9b6b3d8233071d478f7d1e93b498f5a2141941e6.1604994184.git.matti.vaittinen@fi.rohmeurope.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Matti Vaittinen 2020-11-10 10:19:58 +02:00 committed by Mark Brown
parent 1e908b2419
commit b54a27d810
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Documentation/devicetree/bindings/regulator/rohm,bd71847-regulator.yaml
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@ -99,6 +99,55 @@ patternProperties:
Enable/Disable control of this regulator must be left to the
PMIC hardware state machine.
type: boolean
# Setups where regulator (especially the buck8) output voltage is scaled
# by adding external connection where some other regulator output is
# connected to feedback-pin (over suitable resistors) is getting popular
# amongst users of BD71837. (This allows for example scaling down the
# buck8 voltages to suit lover GPU voltages for projects where buck8 is
# (ab)used to supply power for GPU.
#
# So we allow describing this external connection from DT and scale the
# voltages accordingly. This is what the connection should look like:
#
# |---------------|
# | buck 8 |-------+----->Vout
# | | |
# |---------------| |
# | |
# | |
# +-------+--R2----+
# |
# R1
# |
# V FB-pull-up
#
# Here the buck output is sifted according to formula:
#
# Vout_o = Vo - (Vpu - Vo)*R2/R1
# Linear_step = step_orig*(R1+R2)/R1
#
# where:
# Vout_o is adjusted voltage output at vsel reg value 0
# Vo is original voltage output at vsel reg value 0
# Vpu is the pull-up voltage V FB-pull-up in the picture
# R1 and R2 are resistor values.
rohm,fb-pull-up-microvolt:
description:
Feedback-pin has pull-up connection to adjust voltage range. This is
the used pull-up voltage before R1.
rohm,feedback-pull-up-r1-ohms:
description:
Feedback-pin has pull-up connection to adjust voltage range. This is
the used R1 resistor.
rohm,feedback-pull-up-r2-ohms:
description:
Feedback-pin has pull-up connection to adjust voltage range. This is
the used R2 resistor.
required:
- regulator-name