linux-kernel - Re: [[PATCH v2] 1/9] dt-bindings: pwm: Document Synopsys DesignWare snps,pwm

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Date:   Wed, 27 Jul 2022 14:02:26 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Ben Dooks <ben.dooks@...ive.com>, linux-pwm@...r.kernel.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>,
        u.kleine-koenig@...gutronix.de,
        Thierry Reding <thierry.reding@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Greentime Hu <greentime.hu@...ive.com>
Subject: Re: [[PATCH v2] 1/9] dt-bindings: pwm: Document Synopsys DesignWare
 snps,pwm

On 27/07/2022 12:32, Ben Dooks wrote:
> On 26/07/2022 12:05, Krzysztof Kozlowski wrote:
>> On 26/07/2022 12:12, Ben Dooks wrote:
>>> On 26/07/2022 11:05, Krzysztof Kozlowski wrote:
>>>> On 25/07/2022 23:21, Ben Dooks wrote:
>>>>> Add documentation for the bindings for Synopsys' DesignWare PWM block
>>>>> as we will be adding DT/platform support to the Linux driver soon.
>>>>>
>>>>> Signed-off-by: Ben Dooks <ben.dooks@...ive.com>
>>>>> --
>>>>
>>>> This is not proper delimiter and causes the changelog to end up in commit.
>>>>
>>>> Correct also wrong formatting of subject PATCH.
>>>
>>> I realised that once sent and forgot the cover letter.
>>> Maybe I'll try some more post covid recovery.
>>>
>>>>> v2:
>>>>> - fix #pwm-cells to be 3
>>>>> - fix indentation and ordering issues
>>>>> ---
>>>>>    .../devicetree/bindings/pwm/snps,pwm.yaml     | 40 +++++++++++++++++++
>>>>>    1 file changed, 40 insertions(+)
>>>>>    create mode 100644 Documentation/devicetree/bindings/pwm/snps,pwm.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/pwm/snps,pwm.yaml b/Documentation/devicetree/bindings/pwm/snps,pwm.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..594085e5e26f
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/pwm/snps,pwm.yaml
>>>>> @@ -0,0 +1,40 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>> +# Copyright (C) 2022 SiFive, Inc.
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: http://devicetree.org/schemas/pwm/snps,pwm.yaml#
>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>> +
>>>>> +title: Synopsys PWM controller
>>>>> +
>>>>> +maintainers:
>>>>> +  - Ben Dooks <ben.dooks@...ive.com>
>>>>> +
>>>>> +allOf:
>>>>> +  - $ref: pwm.yaml#
>>>>> +
>>>>> +properties:
>>>>> +  compatible:
>>>>> +    const: snps,pwm
>>>>
>>>> This is very generic compatible. I doubt that you cover here all
>>>> Synopsys PWM designs, past and future. You need a specific compatible.
>>>
>>>   From what I can get from the documentation (2.13a) there hasn't been
>>> a huge external interface change and what has been added is all part
>>> of synthesis time options.
>>
>> But you have some specific version, right? Usually these blocks are
>> versioned, so you must include it. I would even argue that such generic
>> compatible should not be used as fallback at all, because it is simply
>> to generic (PWM is not some model name but common acronym),
> 
> I suppose dw-apb-timers is the actual document name, but that's already
> been used for the timer mode in a number of SoCs so probably isn't going
> to be useful. dw-apb-timers-pwm might be a better prefix if snps,pwm is
> not going to be acceptable. (Yes, the block can be built as either a
> PWM or a generic interrupt generating timer at IP generation time)
> 
> As for the version numbers, we could have the -v.vv suffix for these
> blocks, but the v2.xx log has 22 entries already and only one feature
> for programming (which is also a configurable one so can't be just
> enabled by default - it's the 0/100 mode flag in the control registers).
> 
> I'm not sure what the v1.xx timers had, but I don't have access to this
> information and we're getting these documents as second-generation so I
> am not sure if we can get a v1.xx at-all (I suspect this is also going
> to have a number of revisions and about 1 useful register api change
> which would be the "new mode" double counter method which we currently
> rely on having being implicitly enabled by the IP builder (again this
> feature is still something that can be configured on IP genaration))

But why would you need v1.xx documentation?

> 
> Given the configurability of the core, the version numbers might be
> usable at some point, but it does seem to be a lot of churn for what
> currently can be described by one boolean for the 0/100 feature that
> might-be available. Is there a way of saying the compatible string
> can be dw-apb-timers-pwm-2.[0-9][0-9][a-z] ?

I don't understand why. Aren't you documenting here only v2.13a version?

Best regards,
Krzysztof