Re: [v2 1/2] dt-bindings: Add bindings for aspeed pwm-tach and pwm.

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On 2021/4/15, 10:44 PM,Rob Herringwrote:

    >On Wed, Apr 14, 2021 at 10:44 PM Billy Tsai <billy_tsai@xxxxxxxxxxxxxx> wrote:
    >>
    >> Hi Rob,
    >>
    >> On 2021/4/15, 6:16 AM,Rob Herringwrote:
    >>
    >>     On Wed, Apr 14, 2021 at 06:49:38PM +0800, Billy Tsai wrote:
    >>     >> This patch adds device bindings for aspeed pwm-tach device which is a
    >>     >> multi-function device include pwn and tach function and pwm device which
    >>     >> should be the sub-node of pwm-tach device.
    >>     >>
    >>     >> Signed-off-by: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
    >>     >> Change-Id: I18d9dea14c3a04e1b7e38ffecd49d45917b9b545
    >>     >
    >>     >Drop
    >>     >
    >>     >> ---
    >>     >>  .../bindings/mfd/aspeed,ast2600-pwm-tach.yaml | 60 +++++++++++++++++++
    >>     >>  .../bindings/pwm/aspeed,ast2600-pwm.yaml      | 44 ++++++++++++++
    >>     >>  2 files changed, 104 insertions(+)
    >>     >>  create mode 100644 Documentation/devicetree/bindings/mfd/aspeed,ast2600-pwm-tach.yaml
    >>     >>  create mode 100644 Documentation/devicetree/bindings/pwm/aspeed,ast2600-pwm.yaml
    >>     >>
    >>     >> diff --git a/Documentation/devicetree/bindings/mfd/aspeed,ast2600-pwm-tach.yaml b/Documentation/devicetree/bindings/mfd/aspeed,ast2600-pwm-tach.yaml
    >>     >> new file mode 100644
    >>     >> index 000000000000..eaf8bdf8d44e
    >>     >> --- /dev/null
    >>     >> +++ b/Documentation/devicetree/bindings/mfd/aspeed,ast2600-pwm-tach.yaml
    >>     >> @@ -0,0 +1,60 @@
    >>     >> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
    >>     >> +# Copyright (C) 2021 ASPEED, Inc.
    >>     >> +%YAML 1.2
    >>     >> +---
    >>     >> +$id: http://devicetree.org/schemas/mfd/aspeed,ast2600-pwm-tach.yaml#
    >>     >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
    >>     >> +
    >>     >> +title: PWM Tach controller Device Tree Bindings
    >>     >> +
    >>     >> +description: |
    >>     >> +  The PWM Tach controller is represented as a multi-function device which
    >>     >> +  includes:
    >>     >> +    PWM
    >>     >> +    Tach
    >>
    >>     > But is it really? A PWM and tach sounds like a fan controller. Look at
    >>
    >> Our PWM is not only for fans but also used for the motor, led, buzzer, and so on.
    >> So I want to split the function into two devices with a multi-function device.
    >> One for PWM output and one for tach monitor.
    >>
    >>     > other existing PWM+tach bindings we have for fans.
    >>
    >> I didn't see the PWM+tach bindings can you give some example for me, thanks.
    >
    >Let me grep 'tach' for you:
    >
    >Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt
    >Documentation/devicetree/bindings/hwmon/npcm750-pwm-fan.txt
    >
    >Hey, look at that, there's already one for ASpeed. So the question is
    >how is the newer h/w different?
    >>
    >>     >> +
    >>     >> +maintainers:
    >>     >> +  - Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
    >>     >> +
    >>     >> +properties:
    >>     >> +  compatible:
    >>     >> +    items:
    >>     >> +      - enum:
    >>     >> +          - aspeed,ast2600-pwm-tach
    >>     >> +      - const: syscon
    >>     >> +      - const: simple-mfd
    >>     >> +  reg:
    >>     >> +    maxItems: 1
    >>     >> +  "#address-cells":
    >>     >> +    const: 1
    >>     >> +  "#size-cells":
    >>     >> +    const: 1
    >>     >> +
    >>     >> +required:
    >>     >> +  - compatible
    >>     >> +  - reg
    >>     >> +  - "#address-cells"
    >>     >> +  - "#size-cells"
    >>     >> +
    >>     >> +additionalProperties:
    >>     >> +  type: object
    >>
    >>     > As you know the 2 node names, they should be documented. However, see
    >>     > below.
    >>
    >>     >> +
    >>     >> +examples:
    >>     >> +  - |
    >>     >> +    pwm_tach: pwm_tach@1e610000 {
    >>     >> +      compatible = "aspeed,ast2600-pwm-tach", "syscon", "simple-mfd";
    >>     >> +      #address-cells = <1>;
    >>     >> +      #size-cells = <1>;
    >>     >> +      reg = <0x1e610000 0x100>;
    >>     >> +
    >>     >> +      pwm: pwm@0 {
    >>     >> +        compatible = "aspeed,ast2600-pwm";
    >>     >> +        #pwm-cells = <3>;
    >>     >> +        reg = <0x0 0x100>;
    >>     >> +      };
    >>     >> +
    >>     >> +      tach: tach@1 {
    >>     >> +        compatible = "aspeed,ast2600-tach";
    >>     >> +        reg = <0x0 0x100>;
    >>
    >>     > You have 2 nodes at the same address. Not valid.
    >>
    >> Our pwm and tach is used the same base address and the offset is like below:
    >>
    >> PWM0 used 0x0 0x4, Tach0 used 0x8 0xc
    >> PWM1 used 0x10 0x14, Tach1 used 0x18 0x1c
    >> ...
    >>
    >> I will remove the reg property from pwm and tach node and remove the "#address-cells" and
    >> "#size-cells" from the parent node.
    >
    >That's not really the solution...
    >
    >>
    >>     >> +      };
    >>
    >>     > There's no real need for 2 child nodes. The parent node can be a PWM
    >>     > provider.
    >>
    >> However, In our usage, the parent node is a mfd, not a simple PWM device only. I don't want to
    >> combine the different functions with the one device node.
    >
    >Looks like a single h/w block to me. If you want to divide that up
    >into multiple drivers, then that's an OS problem. A single node can be
    >multiple providers. For example, on the existing aspeed binding, just
    >add '#pwm-cells' to the node if you want to also expose it as a PWM
    >provider.
    >
    >Rob

I don't think the pwm/tach should be a single h/w block. 
See the kontron,sl28cpld.yaml:
hwmon@b {
        compatible = "kontron,sl28cpld-fan";
        reg = <0xb>;
};

pwm@c {
        compatible = "kontron,sl28cpld-pwm";
        reg = <0xc>;
        #pwm-cells = <2>;
};
They can be the different function from the dts.

Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt
Documentation/devicetree/bindings/hwmon/npcm750-pwm-fan.txt

These two devices are specific to the used for fan like
Documentation/devicetree/bindings/hwmon/pwm-fan.txt, but with our usage,
it doesn't just for the fan. In our scenario, the customer wants to
create a pwm-beeper, so he needs one pwm input and he doesn't need the
tach function. If I used the pwm-fan as the beeper's pwm input, it look
weird.
Therefore, I want to split these two functions into different devices.

If my thinking is wrong, please let me know.

Very appreciate.





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