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

From: Billy Tsai
Date: Fri Apr 16 2021 - 04:44:59 EST


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.