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

On Wed, Apr 14, 2021 at 10:44 PM Billy Tsai [off-list ref] 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 [off-list ref]
    >> 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 [off-list ref]
    >> +
    >> +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 at 1e610000 {
    >> +      compatible = "aspeed,ast2600-pwm-tach", "syscon", "simple-mfd";
    >> +      #address-cells = <1>;
    >> +      #size-cells = <1>;
    >> +      reg = <0x1e610000 0x100>;
    >> +
    >> +      pwm: pwm at 0 {
    >> +        compatible = "aspeed,ast2600-pwm";
    >> +        #pwm-cells = <3>;
    >> +        reg = <0x0 0x100>;
    >> +      };
    >> +
    >> +      tach: tach at 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