linux-kernel - Re: [PATCH RESEND v2] dt-bindings: pwm: mediatek: Add compatible for MT7986

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Date:   Thu, 24 Nov 2022 14:33:35 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-pwm@...r.kernel.or,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Fabien Parent <fparent@...libre.com>,
        Zhi Mao <zhi.mao@...iatek.com>,
        Sam Shih <sam.shih@...iatek.com>
Subject: Re: [PATCH RESEND v2] dt-bindings: pwm: mediatek: Add compatible for
 MT7986

On 24/11/2022 13:11, Daniel Golle wrote:
> On Thu, Nov 24, 2022 at 12:30:44PM +0100, Krzysztof Kozlowski wrote:
>> On 24/11/2022 12:03, Daniel Golle wrote:
>>> Add new compatible string for MT7986 PWM and list compatible units for
>>> existing entries. Also make sure the number of pwm1-X clocks is listed
>>> for all supported units.
>>>
>>> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
>>> ---
>>> Changes since v1: list compatibles, fix pwm1-n clocks for all SoCs
>>>
>>> Rebased on linux-next and re-run scripts/get_maintainers.pl on patch to
>>> makes sure dt maintainers are included. This has been requested by
>>> Krzysztof Kozlowski.
>>>
>>>  .../devicetree/bindings/pwm/pwm-mediatek.txt  | 20 +++++++++++--------
>>>  1 file changed, 12 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/pwm/pwm-mediatek.txt b/Documentation/devicetree/bindings/pwm/pwm-mediatek.txt
>>> index 554c96b6d0c3..952a338e06e7 100644
>>> --- a/Documentation/devicetree/bindings/pwm/pwm-mediatek.txt
>>> +++ b/Documentation/devicetree/bindings/pwm/pwm-mediatek.txt
>>> @@ -2,14 +2,15 @@ MediaTek PWM controller
>>>  
>>>  Required properties:
>>>   - compatible: should be "mediatek,<name>-pwm":
>>> -   - "mediatek,mt2712-pwm": found on mt2712 SoC.
>>> +   - "mediatek,mt2712-pwm", "mediatek,mt6795-pwm": found on mt2712 SoC.
>>>     - "mediatek,mt6795-pwm": found on mt6795 SoC.
>>> -   - "mediatek,mt7622-pwm": found on mt7622 SoC.
>>> -   - "mediatek,mt7623-pwm": found on mt7623 SoC.
>>> +   - "mediatek,mt7622-pwm", "mediatek,mt8195-pwm", "mediatek,mt8183-pwm", "mediatek,mt7986-pwm": found on mt7622 SoC.
>>
>> This does not look right. What you are saying is mt7622 is compatible
>> with mt8195, which is compatible with mt8183, which is compatible with
>> mt7986. It could be true, but I feel you wanted to say something else -
>> mt7622 is compatible with one SoC which is generic and common to all
>> other implementations.
> 
> MT7622 has 6 PWM channels, it does have CK_26M_SEL register and does
> not need pwm45_fixup. Hence, when using a driver made for MT8195, only
> 4 out of 6 channels woukd work. MT8183 PWM is identical to MT8195,
> hence also compatible. When using driver for MT7986, only 2 channels
> would work, but otherwise it is also compatible.
> 
> So unfortunately, that one generic implementation ("common ancestor")
> does not exist and development of the PWM unit found in MediaTek SoCs
> did not necessarily increase features in more recent iterations, but
> rather just reduce or increase the number of PWM channels available.
> Ironically, the unit with least features (only 2 channels) is found in
> the most recent SoC (MT7986).

None of these explain listing four compatibles.

> 
>>
>>> +   - "mediatek,mt7623-pwm", "mediatek,mt7628-pwm": found on mt7623 SoC.
>>>     - "mediatek,mt7628-pwm": found on mt7628 SoC.
>>>     - "mediatek,mt7629-pwm": found on mt7629 SoC.
>>> -   - "mediatek,mt8183-pwm": found on mt8183 SoC.
>>> -   - "mediatek,mt8195-pwm", "mediatek,mt8183-pwm": found on mt8195 SoC.
>>> +   - "mediatek,mt7986-pwm": found on mt7986 SoC.
>>> +   - "mediatek,mt8183-pwm", "mediatek,mt7986-pwm": found on mt8183 SoC.
>>> +   - "mediatek,mt8195-pwm", "mediatek,mt8183-pwm", "mediatek,mt7986-pwm": found on mt8195 SoC.
>>
>> This as well looks excessive.
> 
> I agree. But it's difficult to say which one should be ommitted.

Best regards,
Krzysztof