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

[Rob Herring]

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