linux-kernel - Re: [PATCH v2 1/4] dt-bindings: rtc: ingenic: Rework compatible strings and add #clock-cells

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Message-Id: <WNUMKR.BWKAZLU4SGE52@crapouillou.net>
Date:   Mon, 31 Oct 2022 19:40:44 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Rob Herring <robh@...nel.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        od@...ndingux.net
Subject: Re: [PATCH v2 1/4] dt-bindings: rtc: ingenic: Rework compatible
 strings and add #clock-cells

Hi Rob,

Le lun. 31 oct. 2022 à 14:23:41 -0500, Rob Herring <robh@...nel.org> a 
écrit :
> On Fri, Oct 28, 2022 at 11:55:16PM +0100, Paul Cercueil wrote:
>>  The RTC in the JZ4770 is compatible with the JZ4760, but has an 
>> extra
>>  register that permits to configure the behaviour of the CLK32K pin. 
>> The
>>  same goes for the RTC in the JZ4780.
>> 
>>  Therefore, the ingenic,jz4770-rtc and ingenic,jz4780-rtc strings do 
>> not
>>  fall back anymore to ingenic,jz4760-rtc. The ingenic,jz4780-rtc 
>> string
>>  now falls back to the ingenic,jz4770-rtc string.
> 
> This is a compatibility mess. There is no driver support in v6.1-rc 
> for
> ingenic,jz4770-rtc, so a new DT would not work with existing kernels. 
> It
> sounds like you need 3 compatibles for 4780.

Do newer DTs need to work with older kernels? I always assumed the 
compatibility was only enforced for the other way around.

If that's the case though, I guess I can enforce 3 compatibles for 4780 
and 2 for 4770 like  you suggested.

Cheers,
-Paul

>> 
>>  Additionally, since the RTCs in the JZ4770 and JZ4780 support 
>> outputting
>>  the input oscillator's clock to the CLK32K pin, the RTC node is now 
>> also
>>  a clock provider on these SoCs, so a #clock-cells property is added.
>> 
>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>  ---
>> 
>>   v2: - add constraint on which SoCs can have the #clock-cells 
>> property
>>       - add JZ4780 example which has a #clock-cells
>> 
>>   .../devicetree/bindings/rtc/ingenic,rtc.yaml  | 32 
>> +++++++++++++++++--
>>   1 file changed, 30 insertions(+), 2 deletions(-)