Re: [PATCH v2 2/2] hwmon: add generic GPIO brownout support

Marco Felsch
2018-11-01T10:40:59Z

On 18-10-30 13:11, Guenter Roeck wrote:
> On Tue, Oct 30, 2018 at 07:34:11PM +0000, Trent Piepho wrote:
> > On Tue, 2018-10-30 at 18:00 +0100, Marco Felsch wrote:
> > > On 18-10-30 06:13, Guenter Roeck wrote:
> > > > On 10/30/18 3:47 AM, Marco Felsch wrote:
> > > > >
> > > hwmon-gpio-simple sounds ok for me.
> > >
> > > > The most difficult part of such a driver would probably be to define acceptable
> > > > devicetree properties.
> > >
> > > That's true! One possible solution could be:
> > >
> > > hwmon_dev {
> > > compatible = "hwmon-gpio-simple";
> > > name = "gpio-generic-hwmon";
> > > update-interval-ms = 100;
> > >
> > > hwmon-gpio-simple,dev@0 {
> > > reg = <0>;
> > > gpio = <gpio3 15 GPIO_ACTIVE_LOW>;
> > > hwmon-gpio-simple,type = "in";
> > > hwmon-gpio-simple,report = "crit_alarm";
> > > };
> > >
> > > hwmon-gpio-simple,dev@1 {
> > > reg = <1>;
> > > gpio = <gpio3 19 GPIO_ACTIVE_LOW>;
> > > hwmon-gpio-simple,type = "temp";
> > > hwmon-gpio-simple,report = "alarm";
> > > };
> > > };
> >
> > Here's some options:
> >
> > hwmon_dev {
> > /* Orthogonal to existing "gpio-fan" binding. */
> > compatible = "gpio-alarm";
> > /* Standard DT property for GPIO users is [<name>-]gpios */
> > alarm-gpios = <&gpio3 15 GPIO_ACTIVE_LOW>,
> > <&gpio3 19 GPIO_ACTIVE_LOW>;
> > /* A <prop>-names property is also a DT standard */
> > alarm-gpios-names = "in0", "temp0";
>
> temp1, and it would have to specify which alarm, but, yes, that would
> be better.
>
> > };
> >
> > The driver can create hwmon alarm attribute(s) based on the name(s). I
> > used "alarm" as it seemed to fit the pattern established by the "fan"
> > driver. Both the gpio-fan and gpio-alarm driver use gpios, but I think
> > considering them one driver for that reason does not make sense.
> >
> > The names are very Linuxy, something that is not liked in DT bindings.
> > It also doesn't extend well if you need to add more attributes to each
> > alarm. Here's something that's more like what I did for the gpio-leds
> > binding.
> >
> > hwmon_dev {
> > compatible = "gpio-alarm";
> > voltage@0 {
> > label = "Battery Voltage Low";
> > type = "voltage";
> > alarm-gpios = <&gpio3 15 GPIO_ACTIVE_LOW>;
> > };
> > cputemp@0 {
> > label = "CPU Temperature Critical";
> > type = "temperature";
> > interrupt-parent = <&gpio3>;
> > interrupts = <19 IRQ_TYPE_LEVEL_LOW>;
> > };
>
> Even better, though the type of alarm (generic, min, max, lcrit, crit,
> cap, emergency, fault) is still needed. That needs to be specified by
> some explicit means, not with a label (though having a label is ok).

Thanks for your ideas, looks quite nice.

> There could also be more than one alarm per sensor (eg in0_lcrit_alarm,
> in0_min_alarm, in0_max_alarm, in0_crit_alarm), all of which would share
> a single label. Something like
>
> #define GPIO_ALARM_GENERIC 0
> #define GPIO_ALARM_MIN 1
> ...
>
> voltage@0 {

reg = <0>;

I remember that we have to add a reg property if we want to use xyz@0.

> label = "Battery Voltage";
> type = "voltage";
> alarm-type = <GPIO_ALARM_LCRIT, GPIO_ALARM_CRIT>;
> alarm-gpios = <&gpio3 15 GPIO_ACTIVE_LOW
> &gpio3 16 GPIO_ACTIVE_LOW>;
> };
>
> with some better (acceptable) values for "alarm-type" and the actual fields.

Should we use the @<reg> suffix to map it to in<reg>_*_alarm or should
we do something like that:

hwmon_dev {
compatible = "gpio-alarm";

voltage {
bat@0 {
reg = <0>;

label = "Battery Pack1 Voltage";
alarm-type = <GPIO_ALARM_LCRIT, GPIO_ALARM_CRIT>;
interrupt-parent = <&gpio3>;
interrupts = <15 IRQ_TYPE_LEVEL_LOW>,
<16 IRQ_TYPE_EDGE_RISING>;

};

bat@1 {
reg = <1>;

label = "Battery Pack2 Voltage";
alarm-type = <GPIO_ALARM_LCRIT, GPIO_ALARM_CRIT>;
interrupts-extended = <&gpio3 17 IRQ_TYPE_EDGE_FALLING>,
<&gpio4 18 IRQ_TYPE_EDGE_FALLING>;

};
};

temperature {
cputemp {
label = "CPU Temperature Critical";
alarm-type = <GPIO_ALARM_CRIT>;
interrupt-parent = <&gpio3>;
interrupts = <20 IRQ_TYPE_EDGE_FALLING>;
};
};
};

Now the subnodes imply the type. Since the hwmon-gpio-simple should
work interrupt driven all the time we should replace the alarm-gpios by
the interrupt property, so we can use the already existing EDGE
flags, as Trent mentoined. Otherwise we have to asume if
the gpio is low-active then the interrupt should be triggered on a
falling edge.

Marco

> Guenter
>
> > };
> >
> > Supporting interrupts instead of just a gpio would allow for edge
> > triggering.
> >
> > I can also see that someone might want to create some kind of time
> > based hysteresis for circuits that don't have that. While it would be
> > very easy to add a "linux,debounce = <1000>;" property, I imagine that
> > would be rejected as configuration in the DT binding.