linux-kernel - Re: [RFC PATCH v3 4/6] dt-bindings: clock: meson: document A1 SoC audio clock controller driver

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Message-ID: <7f8b3916-ddc1-42e1-a2e5-b5ed42010120@salutedevices.com>
Date: Mon, 22 Apr 2024 00:03:28 +0300
From: Jan Dakinevich <jan.dakinevich@...utedevices.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Rob Herring <robh@...nel.org>
CC: Neil Armstrong <neil.armstrong@...aro.org>, Jerome Brunet
	<jbrunet@...libre.com>, Michael Turquette <mturquette@...libre.com>, Stephen
 Boyd <sboyd@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, Kevin Hilman <khilman@...libre.com>, Martin
 Blumenstingl <martin.blumenstingl@...glemail.com>, Philipp Zabel
	<p.zabel@...gutronix.de>, Jiucheng Xu <jiucheng.xu@...ogic.com>,
	<linux-amlogic@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v3 4/6] dt-bindings: clock: meson: document A1 SoC
 audio clock controller driver



On 4/21/24 21:14, Krzysztof Kozlowski wrote:
> On 20/04/2024 18:15, Jan Dakinevich wrote:
>>
>>
>> On 4/20/24 00:09, Rob Herring wrote:
>>> On Fri, Apr 19, 2024 at 03:58:10PM +0300, Jan Dakinevich wrote:
>>>> Add device tree bindings for A1 SoC audio clock and reset controllers.
>>>>
>>>> Signed-off-by: Jan Dakinevich <jan.dakinevich@...utedevices.com>
>>>> ---
>>>>
>>>> This controller has 6 mandatory and up to 20 optional clocks. To describe
>>>> this, I use 'additionalItems'. It produces correct processed-schema.json:
>>>>
>>>>   "clock-names": {
>>>>       "maxItems": 26,
>>>>       "items": [
>>>>           {
>>>>               "const": "pclk"
>>>>           },
>>>>           {
>>>>               "const": "dds_in"
>>>>           },
>>>>           {
>>>>               "const": "fclk_div2"
>>>>           },
>>>>           {
>>>>               "const": "fclk_div3"
>>>>           },
>>>>           {
>>>>               "const": "hifi_pll"
>>>>           },
>>>>           {
>>>>               "const": "xtal"
>>>>           }
>>>>       ],
>>>>       "additionalItems": {
>>>>           "oneOf": [
>>>>               {
>>>>                   "pattern": "^slv_sclk[0-9]$"
>>>>               },
>>>>               {
>>>>                   "pattern": "^slv_lrclk[0-9]$"
>>>>               }
>>>>           ]
>>>>       },
>>>>       "type": "array",
>>>>       "minItems": 6
>>>>   },
>>>>
>>>> and it behaves as expected. However, the checking is followed by
>>>> complaints like this:
>>>>
>>>>   Documentation/devicetree/bindings/clock/amlogic,a1-audio-clkc.yaml: properties:clock-names:additionalItems: {'oneOf': [{'pattern': '^slv_sclk[0-9]$'}, {'pattern': '^slv_lrclk[0-9]$'}]} is not of type 'boolean'
>>>>
>>>> And indeed, 'additionalItems' has boolean type in meta-schema. So, how to
>>>> do it right?
>>>
>>> The meta-schemas are written both to prevent nonsense that json-schema 
>>> allows by default (e.g additionalitems (wrong case)) and constraints to 
>>> follow the patterns we expect. I'm happy to loosen the latter case if 
>>> there's really a need. 
>>>
>>> Generally, most bindings shouldn't be using 'additionalItems' at all as 
>>> all entries should be defined, but there's a few exceptions. Here, the 
>>> only reasoning I see is 26 entries is a lot to write out, but that 
>>> wouldn't really justify it. 
>>
>> Writing a lot of entries don't scary me too much, but the reason is that
>> the existence of optional clock sources depends on schematics. Also, we
> 
> Aren't you documenting SoC component, not a board? 

Yes, I'm documenting SoC component. And the feature of this component is
that its external clock inputs are not mandatory.

> So how exactly it
> depends on schematics? SoC is done or not done...
> 

Schematics determines which external clock sources exist.

>> unable to declare dt-nodes for 'clocks' array in any generic way,
>> because their declaration would depends on that what is actually
>> connected to the SoC (dt-node could be "fixed-clock" with specific rate
>> or something else).
> 
> So these are clock inputs to the SoC?
> 

Yes, these are clock inputs to the SoC, and external hardware could be
connected to them.

>>
>> By the way, I don't know any example (neither for A1 SoC nor for other
>> Amlogic's SoCs) where these optional clocks are used, but they are
>> allowed by hw.
>>
>> This is my understanding of this controller. I hope, Jerome Brunet will
>> clarify how it actually works.
> 
> Best regards,
> Krzysztof
> 

-- 
Best regards
Jan Dakinevich