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

[Guenter Roeck <linux@roeck-us.net>]

On 11/1/18 3:40 AM, Marco Felsch wrote:
> 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

Note that this isn't entirely correct: If the gpio pin doesn't support
interrupts, the driver would just report the state of the pin.

Guenter

> 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.
>