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    SubjectRe: [PATCH v2 1/3] dt-bindings: rtc: pcf8523: add DSM pm option for battery switch-over
    On Mon, Jul 27, 2020 at 03:33:17PM +0200, Jon Nettleton wrote:
    > On Mon, Jul 27, 2020 at 11:46 AM Russell King - ARM Linux admin
    > <linux@armlinux.org.uk> wrote:
    > >
    > > On Thu, Jul 23, 2020 at 09:57:55PM +0200, Alexandre Belloni wrote:
    > > > On 23/07/2020 11:49:05-0600, Rob Herring wrote:
    > > > > On Mon, Jul 20, 2020 at 12:23:59PM +0100, miguelborgesdefreitas@gmail.com wrote:
    > > > > > From: Miguel Borges de Freitas <miguelborgesdefreitas@gmail.com>
    > > > > >
    > > > > > This adds direct-switching mode as a configurable DT flag for
    > > > > > RTC modules supporting it (e.g. nxp pcf8523).
    > > > > > DSM switches the power source to the battery supply whenever the
    > > > > > VDD drops below VBAT. The option is recommended for hw designs
    > > > > > where VDD is always expected to be higher than VBAT.
    > > > > >
    > > > > > Signed-off-by: Miguel Borges de Freitas <miguelborgesdefreitas@gmail.com>
    > > > > > ---
    > > > > > Changes in v2:
    > > > > > - Added extended commit message for git history
    > > > > > - Separate dt bindings documentation into a single patch
    > > > > >
    > > > > > Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt | 7 ++++++-
    > > > > > Documentation/devicetree/bindings/rtc/rtc.yaml | 7 +++++++
    > > > > > 2 files changed, 13 insertions(+), 1 deletion(-)
    > > > > >
    > > > > > diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
    > > > > > index 0b1080c..f715a8f 100644
    > > > > > --- a/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
    > > > > > +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf8523.txt
    > > > > > @@ -4,10 +4,14 @@ Required properties:
    > > > > > - compatible: Should contain "nxp,pcf8523".
    > > > > > - reg: I2C address for chip.
    > > > > >
    > > > > > -Optional property:
    > > > > > +Optional properties:
    > > > > > - quartz-load-femtofarads: The capacitive load of the quartz(x-tal),
    > > > > > expressed in femto Farad (fF). Valid values are 7000 and 12500.
    > > > > > Default value (if no value is specified) is 12500fF.
    > > > > > +- pm-enable-dsm: battery switch-over function is enabled in direct
    > > > > > + switching mode. The power failure condition happens when VDD < VBAT,
    > > > > > + without requiring VDD to drop below Vth(sw)bat.
    > > > > > + Default value (if not provided) is the standard mode.
    > > > > >
    > > > > > Example:
    > > > > >
    > > > > > @@ -15,4 +19,5 @@ pcf8523: rtc@68 {
    > > > > > compatible = "nxp,pcf8523";
    > > > > > reg = <0x68>;
    > > > > > quartz-load-femtofarads = <7000>;
    > > > > > + pm-enable-dsm;
    > > > > > };
    > > > > > diff --git a/Documentation/devicetree/bindings/rtc/rtc.yaml b/Documentation/devicetree/bindings/rtc/rtc.yaml
    > > > > > index ee237b2..a0048f4 100644
    > > > > > --- a/Documentation/devicetree/bindings/rtc/rtc.yaml
    > > > > > +++ b/Documentation/devicetree/bindings/rtc/rtc.yaml
    > > > > > @@ -47,4 +47,11 @@ properties:
    > > > > > description:
    > > > > > Enables wake up of host system on alarm.
    > > > > >
    > > > > > + pm-enable-dsm:
    > > > > > + $ref: /schemas/types.yaml#/definitions/flag
    > > > > > + description:
    > > > > > + Enables the battery switch-over function in direct switching
    > > > > > + mode. Should be set in systems where VDD is higher than VBAT
    > > > > > + at all times.
    > > > >
    > > > > I'm all for common properties, but is this common across vendors?
    > > > >
    > > >
    > > > This is but this shouldn't be a DT property as it has to be changed
    > > > dynamically. I'm working on an ioctl interface to change this
    > > > configuration.
    > >
    > > Why does it need to be changed dynamically? If the hardware components
    > > are not fitted to allow the RTC to be safely used without DSM, then
    > > why should userspace be able to disable DSM?
    > >
    >
    > My presumption would be if you had a system that ran at different
    > system voltages depending if it is plugged in to mains or running on a
    > battery.

    Yes, but we're not talking about that case with the Cubox-i.

    Should a platform like the Cubox-i allow the user to disable DSM?

    There needs to be a way to block the ability to dynamically change
    this mode if the hardware is not up to operating without DSM.

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