Re: [PATCH] dt-bindings: soc: imx8mp-media-blk-ctrl: Add LDB into DT example

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 30/06/2022 21:16, Marek Vasut wrote:
> On 6/30/22 21:11, Krzysztof Kozlowski wrote:
>> On 30/06/2022 19:39, Marek Vasut wrote:
>>> Document the LDB bridge subnode and add the subnode into the example.
>>> For the subnode to work, the block control must be compatible with
>>> simple-mfd in addition to the existing compatibles.
>>>
>>> Signed-off-by: Marek Vasut <marex@denx.de>
>>> Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>> Cc: Lucas Stach <l.stach@pengutronix.de>
>>> Cc: NXP Linux Team <linux-imx@nxp.com>
>>> Cc: Paul Elder <paul.elder@ideasonboard.com>
>>> Cc: Peng Fan <peng.fan@nxp.com>
>>> Cc: Rob Herring <robh+dt@kernel.org>
>>> Cc: devicetree@vger.kernel.org
>>> ---
>>>   .../soc/imx/fsl,imx8mp-media-blk-ctrl.yaml    | 54 ++++++++++++++++++-
>>>   1 file changed, 53 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.yaml b/Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.yaml
>>> index b246d8386ba4a..05a19d3229830 100644
>>> --- a/Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.yaml
>>> +++ b/Documentation/devicetree/bindings/soc/imx/fsl,imx8mp-media-blk-ctrl.yaml
>>> @@ -18,11 +18,18 @@ properties:
>>>     compatible:
>>>       items:
>>>         - const: fsl,imx8mp-media-blk-ctrl
>>> +      - const: simple-mfd
>>
>> Not really... simple-mfd means devices is really simple and you just use
>> it to instantiate children. However this is not simple - it's a power
>> domain controller with several clocks and power domains as input.
>>
>> It's not a simple MFD, but a regular device.
> 
> I don't understand this comment. The LDB bridge is literally two 
> registers with a few bits in this media block controller register area. 
> Can you expand on why the simple-mfd is unsuitable and what should it be 
> instead ?

Looking at the bindings you have there 10 power domains, 10 input clocks
and a domain provider. The driver is also not that simple which is
another argument that this is not simple-mfd. Simply, it is not simple.

What I meant, is that probably you should populate children from the
driver instead of adding simple-mfd compatible. Once you add simple-mfd,
you cannot remove it and children cannot use anything from the parent.

Best regards,
Krzysztof