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Date: Fri, 12 Jan 2024 19:53:48 -0600
From: Rob Herring <robh@...nel.org>
To: Billy Tsai <billy_tsai@...eedtech.com>
Cc: "jdelvare@...e.com" <jdelvare@...e.com>, "linux@...ck-us.net" <linux@...ck-us.net>,
"krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>, "joel@....id.au" <joel@....id.au>,
"andrew@...id.au" <andrew@...id.au>, "corbet@....net" <corbet@....net>,
"thierry.reding@...il.com" <thierry.reding@...il.com>,
"u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
"naresh.solanki@...ements.com" <naresh.solanki@...ements.com>,
"linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>, BMC-SW <BMC-SW@...eedtech.com>,
"patrick@...cx.xyz" <patrick@...cx.xyz>
Subject: Re: [PATCH RESEND v10 2/3] dt-bindings: hwmon: Support Aspeed g6 PWM
TACH Control
On Sun, Nov 26, 2023 at 11:45 PM Billy Tsai <billy_tsai@...eedtech.com> wrote:
>
> > > > > Document the compatible for aspeed,ast2600-pwm-tach device, which can
> > > > > support up to 16 PWM outputs and 16 fan tach input.
> > > > >
> > > > > Signed-off-by: Billy Tsai <billy_tsai@...eedtech.com>
> > > > > ---
> > > > > .../bindings/hwmon/aspeed,g6-pwm-tach.yaml | 69 +++++++++++++++++++
> > > > > 1 file changed, 69 insertions(+)
> > > > > create mode 100644 Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml b/Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml
> > > > > new file mode 100644
> > > > > index 000000000000..c615fb10705c
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml
> > > > > @@ -0,0 +1,69 @@
> > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > +# Copyright (C) 2023 Aspeed, Inc.
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id: http://devicetree.org/schemas/hwmon/aspeed,g6-pwm-tach.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: ASPEED G6 PWM and Fan Tach controller
> > > > > +
> > > > > +maintainers:
> > > > > + - Billy Tsai <billy_tsai@...eedtech.com>
> > > > > +
> > > > > +description: |
> > > > > + The ASPEED PWM controller can support up to 16 PWM outputs.
> > > > > + The ASPEED Fan Tacho controller can support up to 16 fan tach input.
> > > > > + They are independent hardware blocks, which are different from the
> > > > > + previous version of the ASPEED chip.
> > > > > +
> > > > > +properties:
> > > > > + compatible:
> > > > > + enum:
> > > > > + - aspeed,ast2600-pwm-tach
> > > > > +
> > > > > + reg:
> > > > > + maxItems: 1
> > > > > +
> > > > > + clocks:
> > > > > + maxItems: 1
> > > > > +
> > > > > + resets:
> > > > > + maxItems: 1
> > > > > +
> > > > > + "#pwm-cells":
> > > > > + const: 3
> > > > > +
> > > > > +patternProperties:
> > > > > + "^fan-[0-9]+$":
> > > > > + $ref: fan-common.yaml#
> > > > > + unevaluatedProperties: false
> > > > > + required:
> > > > > + - tach-ch
> > > > > +
> > > > > +required:
> > > > > + - reg
> > > > > + - clocks
> > > > > + - resets
> > > > > + - "#pwm-cells"
> > > > > + - compatible
> > > > > +
> > > > > +additionalProperties: false
> > > > > +
> > > > > +examples:
> > > > > + - |
> > > > > + #include <dt-bindings/clock/aspeed-clock.h>
> > > > > + pwm_tach: pwm-tach-controller@...10000 {
> > > > > + compatible = "aspeed,ast2600-pwm-tach";
> > > > > + reg = <0x1e610000 0x100>;
> > > > > + clocks = <&syscon ASPEED_CLK_AHB>;
> > > > > + resets = <&syscon ASPEED_RESET_PWM>;
> > > > > + #pwm-cells = <3>;
> > > > > +
> > > > > + fan-0 {
> > >
> > > > I assume there's a PWM connection here? How do you know which PWM? You
> > > > said the tach channel is independent, so it is not that.
> > >
> > > > It should not be 0 from 'fan-0' because that's just a meaningless index.
> > >
> > > > You either need 'pwms' here or you can use 'reg' and the reg value is
> > > > the PWM channel.
> > >
> > > Hi Rob, this binding is used to export the PWM provider and the Fan monitor (i.e., Tach).
> > > If the user wants to add the PWM connection for the fan, it can be done as follows:
> > >
> > > fan0: pwm-fan0 {
> > > compatible = "pwm-fan";
> > > pwms = <&pwm_tach 0 40000 0>;
> > > cooling-min-state = <0>;
> > > cooling-max-state = <3>;
> > > #cooling-cells = <2>;
> > > cooling-levels = <0 15 128 255>;
> > > };
> > >
> > > This will reuse the existing PWM fan driver (e.g., pwm-fan.c).
>
> > I'm confused now. So what are the child nodes you have? You are
> > defining the fan in 2 places? The "pwm-fan" driver supports a tach via
> > an interrupt, so how would this work in your case?
>
> Hi Rob,
>
> The tach interrupt for the pwm-fan is option. In our case, the dts just reuse the pwm control function
> of the pwm-fan, and the part of the tach monitor will be created by our fan child nodes.
> So the dts will like followings:
>
> // Use to declare the tach monitor for fan.
> &pwm_tach {
> fan-0 {
> tach-ch = /bits/ 8 <0x0>;
> };
> fan-1 {
> tach-ch = /bits/ 8 <0x1>;
> };
> ...
> }
>
> // Reuse the pwm-fan.c to control the behavior of the PWM for fan.
> fan0: pwm-fan0 {
> compatible = "pwm-fan";
> pwms = <&pwm_tach 0 40000 0>; /* Target freq:25 kHz */
> cooling-min-state = <0>;
> cooling-max-state = <3>;
> #cooling-cells = <2>;
> cooling-levels = <0 15 128 255>;
> };
No, you can't have a fan described by 2 different nodes. Can't you
just merge everything from the pwm-fan0 node into the fan-0 node?
Rob
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