[RFC,0/3] regulator: bd718x7: support voltage scaling

RFC for adding a support for typical voltage scaling connection

In few occasions there has been a need to scale the voltage output
from bucks on BD71837. Usually this is done when buck8 is used to
power specific GPU which can utilize voltages down to 0.7V. As lowest
the buck8 on BD71837 can go is 0.8V, and external connection is used to
scale the voltages.

The BD71837, BD71847 and BD71850 bucks can be adjusted by pulling up the
feedback pin using suitable voltage/resistors.

	|---------------|
	|       buck 8  |-------+----->Vout
	|               |       |
	|---------------|       |
	       |                |
	       |                |
	       +-------+--R2----+
	               |
	               R1
	               |
	       V FB-pull-up


This will scale the voltage as follows:
 - 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.

From HW point of view this does not need to be limited to buck 8. This
connection can be used to adjust output from any of the bucks on
BD71837/47/50.

As this seems to be a 'de-facto' way to scale the voltages on BD71837 it
might be a good idea to support computing the new voltage ranges for
bucks based on the V-pull-up and resistor R1/R2 values given from
device-tree. This allows describing the external HW connection using DT
to correctly scale the voltages.

This RFC uses "rohm,feedback-pull-up-r1-ohms" and
"rohm,feedback-pull-up-r2-ohms" to provide the resistor values - but
these names (without the picture) might not be too descriptive. I am
grateful for all suggestions as better and more descriptive names.

This patch series is an RFC because this connection feels somewhat
"hacky". OTOH - when hack becomes widely used, it is less of an hack and
more of a standard - and occasionally supporting HW hacks using SW may
benefit us all, right? :)

The other thing some projects do is allowing the change of BD71837 buck8
voltages when buck8 is enabled. This however will introduce voltage
spikes as buck8 was not originally designed for this. The specific HW
platform must be evaluated to be able to tolerate these spikes. Thus
this patch series does not support buck8 voltage changes when buck8 is
enabled. I wonder if this should be allowed per some config option(?) I
don't want to help people frying their boards... Opinions? Is there
suggested way of allowing this type of features at own risk? Config or
even Some #ifdef which is not listed in Kconfig? Device-tree property?
 If you have (good) suggestions I could add the optional (non default)
DVS support for non DVS bucks on BD71837.


Matti Vaittinen (3):
  dt-bindings: regulator: BD71837 support commonly used feedback
    connection
  dt-bindings: regulator: BD71847 support commonly used feedback
    connection
  regulator: bd718x7: Support external connection to scale voltages

 .../regulator/rohm,bd71837-regulator.yaml     |  48 +++++
 .../regulator/rohm,bd71847-regulator.yaml     |  49 ++++++
 drivers/regulator/bd718x7-regulator.c         | 164 +++++++++++++++++-
 3 files changed, 254 insertions(+), 7 deletions(-)


base-commit: 3cea11cd5e3b00d91caf0b4730194039b45c5891

On Tue, 10 Nov 2020 10:19:16 +0200, Matti Vaittinen wrote:
> RFC for adding a support for typical voltage scaling connection
> 
> In few occasions there has been a need to scale the voltage output
> from bucks on BD71837. Usually this is done when buck8 is used to
> power specific GPU which can utilize voltages down to 0.7V. As lowest
> the buck8 on BD71837 can go is 0.8V, and external connection is used to
> scale the voltages.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next

Thanks!

[1/3] regulator: BD71837 support commonly used feedback connection
      commit: 1e908b2419ea828dfad9819e5c01322a93665356
[2/3] regulator: BD71847 support commonly used feedback connection
      commit: b54a27d8109fc8f18cec3e0663f8e81ea727e3c6
[3/3] regulator: bd718x7: Support external connection to scale voltages
      commit: d2ad981151b3a812e961c8ee0ffd7e349b4027d6

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark