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Date:   Wed, 28 Mar 2018 13:23:21 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Tim Harvey <tharvey@gateworks.com>
Cc:     Lee Jones <lee.jones@linaro.org>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Wim Van Sebroeck <wim@iguana.be>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-hwmon@vger.kernel.org,
        linux-input@vger.kernel.org, linux-watchdog@vger.kernel.org
Subject: Re: [PATCH v3 1/4] dt-bindings: mfd: Add Gateworks System Controller
 bindings
Message-ID: <20180328202321.GA21664@roeck-us.net>
References: <1522250043-8065-1-git-send-email-tharvey@gateworks.com>
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 <20180328162416.GB25325@roeck-us.net>
 <CAJ+vNU2aUN4ME3+RA3DNPO75O6vPBcQpuRSfQJ4_Ns_zQAtCCQ@mail.gmail.com>
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On Wed, Mar 28, 2018 at 12:17:34PM -0700, Tim Harvey wrote:
> On Wed, Mar 28, 2018 at 9:24 AM, Guenter Roeck <linux@roeck-us.net> wrote:
> > On Wed, Mar 28, 2018 at 08:14:00AM -0700, Tim Harvey wrote:
> >> This patch adds documentation of device-tree bindings for the
> >> Gateworks System Controller (GSC).
> >>
> >> Signed-off-by: Tim Harvey <tharvey@gateworks.com>
> >> ---
> >> v3:
> >>  - replaced _ with -
> >>  - remove input bindings
> >>  - added full description of hwmon
> >>  - fix unit address of hwmon child nodes
> >>
> >> ---
> >>  .../devicetree/bindings/mfd/gateworks-gsc.txt      | 135 +++++++++++++++++++++
> >>  1 file changed, 135 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/mfd/gateworks-gsc.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/mfd/gateworks-gsc.txt b/Documentation/devicetree/bindings/mfd/gateworks-gsc.txt
> >> new file mode 100644
> >> index 0000000..8f530ed
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/mfd/gateworks-gsc.txt
> >> @@ -0,0 +1,135 @@
> >> +Gateworks System Controller multi-function device
> >> +
> >> +The GSC is a Multifunction I2C slave device with the following submodules:
> >> +- WDT
> >> +- GPIO
> >> +- Pushbutton controller
> >> +- HWMON
> >> +
> >> +Required properties:
> >> +- compatible : Must be "gw,gsc"
> >> +- reg: I2C address of the device
> >> +- interrupts: interrupt triggered by GSC_IRQ# signal
> >> +- interrupt-parent: Interrupt controller GSC is connected to
> >> +- #interrupt-cells: should be <1>, index of the interrupt within the
> >> +  controller, in accordance with the "one cell" variant of
> >> +  <devicetree/bindings/interrupt-controller/interrupt.txt>
> >> +
> >> +Optional nodes:
> >> +* watchdog:
> >> +The GSC provides a Watchdog monitor which can power cycle the board's
> >> +primary power supply on most board models when tripped.
> >> +
> >> +Required watchdog properties:
> >> +- compatible: must be "gw,gsc-watchdog"
> >> +
> >> +* hwmon:
> >> +The GSC provides a set of Analog to Digitcal Converter (ADC) pins used for
> >> +temperature and/or voltage monitoring.
> >> +
> >> +Required hwmon properties:
> >> +- compatible: must be "gw,gsc-hwmon"
> >> +
> >
> > "hwmon" is a very Linux specific term. It might make sense to find a more
> > generic term.
> 
> The 'hwmon' driver supports child nodes that fall into the following category:
>  - temperature sensor (GSC internal temperature sensor - i2c registers
> returns value in C*10)
>  - voltage rails (two types here; cooked: i2c registers return
> pre-scaled value in mV), raw: i2c registers return a raw ADC value
> that must be scaled based on ADC internal ref voltage and resolution
> and adjusted for a voltage divider to convert to mV
>  - fan setpoints (I'll explain these below)
> 
> I called the node 'gw,gsc-hwmon' because the driver fits into the
> 'hwmon' API. Isn't that appropriate here for the driver compatible
> string?
> 

Devicetree properties are supposed to be OS independent.

> >
> >> +Optional hwmon properties:
> >> +- gw,reference-voltage: ADC reference voltage (mV) used in scaling raw ADCs
> >
> > AFAIK devicetree likes to specify voltages in uV.
> 
> There are currently plenty of dt props specified in mV (grep -r mV
> Documentation/devicetree/bindings/).
> 

"But so many others are speeding, why do I get a ticket ?"

Please discuss with Rob.

> >
> >> +- gw,resolution: ADC resolution (ie 4096) used in scaling raw ADCs
> >> +
> >
> > 4096 what ?
> 
> reference-voltage and resolution are used to scale the values from the
> nodes that report a raw ADC value:
> 
> V = Vadc * (reference-voltage / resolution)
> 
> I can provide that in bits if it makes more sense? I can also hard

Yes, I think that would make more sense, and please describe what it means.

> code both the resolution and the vref in the hwmon driver and remove
> it from dt as currently the only GSC that uses raw ADC values is 12bit
> with 2.5V ref.
> 

That would be even better.

> >
> >> +Each hwmon child node defines an ADC input on the chip which the GSC may
> >> +report cooked values (ie temperature sensor based on thermister), raw values,
> >> +(ie voltage rail with a pre-scaling resistor divider), or a fan controller
> >> +setpoint.
> >> +
> >> +Required hwmon child properties:
> >> +- type: one of the following ADC types:
> >> +  "gw,hwmon-temperature" - reports temperature in C*10
> >> +  "gw,hwmon-voltage" - reports a pre-scaled voltage value
> >> +  "gw,hwmon-voltage-raw" - reports a raw ADC that is scaled with
> >> +       vreference, resolution, and optional resistor divider
> >> +  "gw,hwmon-fan" - a fan temperature setpoint in C*10
> >
> > What is a "fan temperature setpoint" ?
> >
> 
> The GSC supports a fan controller which drives a PWM signal to vary
> the speed of a fan based on the GSC internal temperature sensor. The
> FAN controller has 6 setpoints each having a fixed PWM duty-cycle but
> the temperature at which those setpoints kick in can be varies via
> registers at the 0x29 slave address (same slave address as the
> temperature sensor and voltage inputs which is why I have it in the
> hwmon driver):
> 
> fan0_point - 50% PWM (default 300)
> fan1_point - 60% PWM (default 330)
> fan2_point - 70% PWM (default 360)
> fan3_point - 80% PWM (default 390)
> fan4_point - 90% PWM (default 420)
> fan5_point - 100% PWM (default 450)
> 
> The values are C/10 thus if the internal GSC temp sensor is below 30C
> the fan output will be 0% duty cycle and if it hits 30C it will go to
> 50% until it hits 60% at 33C etc.
> 
Please do not define your own scaling factors. pwm values are 0..255,
and temperatures are in milli-degrees C.

> That is the hardware implementation that I'm trying to abstract and
> define here. You pointed out the fact that the fan*_input ABI is
> read-only fan PWM and I see that now. What do you suggest I use for

No, it isn't. It is the fan speed in RPM.

> this feature I'm trying to implement driver support for?
> 

pwm[1-*]_auto_point[1-*]_pwm
pwm[1-*]_auto_point[1-*]_temp
pwm[1-*]_auto_point[1-*]_temp_hyst

may be relevant. From the context, something like

pwm1_auto_point1_pwm	read-only, set to 128
pwm1_auto_point1_temp	30000
pwm1_auto_point2_pwm	read-only, set to 153
pwm1_auto_point2_temp	33000
pwm1_auto_point3_pwm	read-only, set to 179
pwm1_auto_point3_temp	36000
pwm1_auto_point4_pwm	read-only, set to 204
pwm1_auto_point4_temp	39000
pwm1_auto_point5_pwm	read-only, set to 230
pwm1_auto_point5_temp	42000
pwm1_auto_point6_pwm	read-only, set to 255
pwm1_auto_point6_temp	45000

might make sense.

> I did notice that nouveau_hwmon.c has a single temperature setpoint
> similar to this that they support with SENSOR_DEVICE_ATTR:
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_hwmon.c#L63
> 
Whatever nouveau_hwmon.c does is, for all practical purposes, absolutely
irrelevant. This code has never been reviewed by a hwmon maintainer.
It may (or may not) be complete junk. Please do not use anything outside
drivers/hwmon as example.

> >> +- reg: offset of the ADC register
> >> +- label: name of the ADC input or FAN setpoint
> >> +
> >> +Optional hwmon child properties:
> >> +- gw,voltage-divider: An array of two integers containing the resistor
> >> +  values R1 and R2 of the optinal resistor divider on a raw ADC
> >> +- gw,voltage-offset: a mV voltage offset to apply to a raw ADC (ie to
> >> +  compensate for a diode drop)
> >> +
> >> +Example:
> >> +
> >> +     gsc: gsc@20 {
> >> +             compatible = "gw,gsc";
> >> +             reg = <0x20>;
> >> +             interrupt-parent = <&gpio1>;
> >> +             interrupts = <4 GPIO_ACTIVE_LOW>;
> >> +             interrupt-controller;
> >> +             #interrupt-cells = <1>;
> >> +
> >> +             watchdog {
> >> +                     compatible = "gw,gsc-watchdog";
> >> +             };
> >> +
> >> +             hwmon {
> >> +                     compatible = "gw,gsc-hwmon";
> >> +                     #address-cells = <1>;
> >> +                     #size-cells = <0>;
> >> +                     gw,reference-voltage = <2500>;
> >> +                     gw,resolution = <4096>;
> >> +
> >> +                     hwmon@0 { /* A0: Board Temperature */
> >> +                             type = "gw,hwmon-temperature";
> >> +                             reg = <0x00>;
> >> +                             label = "temp";
> >> +                     };
> >> +
> >> +                     hwmon@2 { /* A1: Input Voltage (raw ADC) */
> >> +                             type = "gw,hwmon-voltage-raw";
> >> +                             reg = <0x02>;
> >> +                             label = "vdd_vin";
> >> +                             gw,voltage-divider = <22100 1000>;
> >> +                             gw,voltage-offset = <800>;
> >> +                     };
> >> +
> >> +                     hwmon@b { /* A2: Battery voltage */
> >> +                             type = "gw,hwmon-voltage";
> >> +                             reg = <0x0b>;
> >> +                             label = "vdd_bat";
> >> +                     };
> >> +
> >> +                     hwmon@2c { /* fan temperature setpoint for 50% duty */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x2c>;
> >> +                             label = "fan_50p";
> >> +                     };
> >> +
> >> +                     hwmon@2e { /* fan1 */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x2e>;
> >> +                             label = "fan_60p";
> >> +                     };
> >> +
> >> +                     hwmon@30 { /* fan2 */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x30>;
> >> +                             label = "fan_70p";
> >> +                     };
> >> +
> >> +                     hwmon@32 { /* fan3 */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x32>;
> >> +                             label = "fan_80p";
> >> +                     };
> >> +
> >> +                     hwmon@34 { /* fan4 */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x34>;
> >> +                             label = "fan_90p";
> >> +                     };
> >> +
> >> +                     hwmon@36 { /* fan5 */
> >> +                             type = "gw,hwmon-fan";
> >> +                             reg = <0x36>;
> >> +                             label = "fan_100p";
> >> +                     };
> >
> > No idea what this is supposed to be doing, but whatever it is,
> > it appears to be wrong. I'll comment more on it in the hwmon driver.
> >
> 
> ok - I'll respond to that thread.
> 
> Thanks for the review!
> 
> Tim