[PATCH v3 1/3] dt-bindings: arm: fsl: add mu binding doc

[o.rempel@pengutronix.de (Oleksij Rempel)]

On 17.07.2018 08:50, A.s. Dong wrote:
>> -----Original Message-----
>> From: Oleksij Rempel [mailto:o.rempel at pengutronix.de]
>> Sent: Tuesday, July 17, 2018 2:32 PM
>> To: A.s. Dong <aisheng.dong@nxp.com>; Shawn Guo
>> <shawnguo@kernel.org>; Fabio Estevam <fabio.estevam@nxp.com>; Rob
>> Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>
>> Cc: devicetree at vger.kernel.org; kernel at pengutronix.de; linux-arm-
>> kernel at lists.infradead.org; dl-linux-imx <linux-imx@nxp.com>
>> Subject: Re: [PATCH v3 1/3] dt-bindings: arm: fsl: add mu binding doc
>>
>>
>>
>> On 17.07.2018 08:26, A.s. Dong wrote:
>>>> -----Original Message-----
>>>> From: Oleksij Rempel [mailto:o.rempel at pengutronix.de]
>>>> Sent: Tuesday, July 17, 2018 1:45 PM
>>>> To: A.s. Dong <aisheng.dong@nxp.com>; Shawn Guo
>>>> <shawnguo@kernel.org>; Fabio Estevam <fabio.estevam@nxp.com>;
>> Rob
>>>> Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>
>>>> Cc: devicetree at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
>>>> kernel at pengutronix.de; dl-linux-imx <linux-imx@nxp.com>
>>>> Subject: Re: [PATCH v3 1/3] dt-bindings: arm: fsl: add mu binding doc
>>>>
>>>>
>>>>
>>>> On 17.07.2018 07:00, A.s. Dong wrote:
>>>>>> -----Original Message-----
>>>>>> From: Oleksij Rempel [mailto:o.rempel at pengutronix.de]
>>>>>> Sent: Monday, July 16, 2018 7:42 PM
>>>>>> To: Shawn Guo <shawnguo@kernel.org>; Fabio Estevam
>>>>>> <fabio.estevam@nxp.com>; Rob Herring <robh+dt@kernel.org>; Mark
>>>>>> Rutland <mark.rutland@arm.com>; A.s. Dong
>> <aisheng.dong@nxp.com>
>>>>>> Cc: Oleksij Rempel <o.rempel@pengutronix.de>;
>>>>>> kernel at pengutronix.de; linux-arm-kernel at lists.infradead.org;
>>>>>> devicetree at vger.kernel.org;
>>>>>> dl-linux- imx <linux-imx@nxp.com>
>>>>>> Subject: [PATCH v3 1/3] dt-bindings: arm: fsl: add mu binding doc
>>>>>>
>>>>>> The Messaging Unit module enables two processors within the SoC to
>>>>>> communicate and coordinate by passing messages (e.g. data, status
>>>>>> and
>>>>>> control) through the MU interface.
>>>>>>
>>>>>> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
>>>>>> ---
>>>>>>  .../devicetree/bindings/mailbox/fsl,mu.txt    | 32
>>>> +++++++++++++++++++
>>>>>>  1 file changed, 32 insertions(+)
>>>>>>  create mode 100644
>>>>>> Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>>>> b/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>>>> new file mode 100644
>>>>>> index 000000000000..5d48dd75b98d
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>>>> @@ -0,0 +1,32 @@
>>>>>> +NXP i.MX Messaging Unit (MU)
>>>>>> +------------------------------------------------------------------
>>>>>> +--
>>>>>> +
>>>>>> +Required properties:
>>>>>> +-------------------
>>>>>> +- compatible :	should be "fsl,<chip>-mu", the supported chips
>>>> include:
>>>>>> +		imx6sx	- i.MX 6SoloX
>>>>>> +		imx7d	- i.MX 7Dual
>>>>>> +		imx7s	- i.MX 7Solo
>>>>>> +		imx7ulp	- i.MX 7ULP
>>>>>> +		imx8qm	- i.MX 8QM
>>>>>> +		imx8qxp	- i.MX 8QXP
>>>>>> +- reg :		Should contain the registers location and length
>>>>>> +- interrupts :	Interrupt number. The interrupt specifier format
>>>> depends
>>>>>> +		on the interrupt controller parent.
>>>>>> +- #mbox-cells:  Must be:
>>>>>> +		0 - for single channel mode. i.MX8* SCU protocol specific.
>>>>>> +		1 - for multichannel (generic) mode.
>>>>>> +
>>>>>> +Optional properties:
>>>>>> +-------------------
>>>>>> +- clocks :	phandle to the input clock.
>>>>>> +- fsl,mu-side-a : Should be set for side A MU.
>>>>>
>>>>> For this property, how about doing like:
>>>>> fsl,mu-side: An Integer represents the MU side.
>>>>
>>>> All this SoCs have MUs with only two sides. Why do we need explicit
>>>> annotation for both parts?
>>>>
>>>>> If missing this property, it's default to Side A
>>>>
>>>> So, why do we need optional integer, which is set by default as side A?
>>>> This is why I made it bool.
>>>
>>> Yes, A bool probably is better.
>>>
>>>>
>>>>> 	       which is mostly used by A core.
>>>>
>>>> And you will need to explicit set side=B for SCU. Correct?
>>>
>>> SCU is using side A. AFAIK all SoC A core is using side A by default.
>>> That's why I think it can be default one. User is free to specify both
>>> In device tree. Does it make sense to you?
>>
>> Ok.
> 
> My original assumption is we can specify the side explicitly in device tree
>  (default to side A if missing) like:
> mu0a: mailbox at 30aa0000 {
>         compatible = "fsl,imx7s-mu";
>         ...
>         fsl,mu-side = <0>;
> };
> 
> mu0b: mailbox at 30ab0000 {
>         compatible = "fsl,imx7s-mu";
>         ...
>         fsl,mu-side = <1>;
> };
> 
> But you're right it can be simply indicated by a bool as well.
> mu0a: mailbox at 30aa0000 {
>         compatible = "fsl,imx7s-mu";
>         ...
> };
> 
> mu0b: mailbox at 30ab0000 {
>         compatible = "fsl,imx7s-mu";
>         ...
>         fsl,mu-side-b; 
> };
> 
> I'm okay with both. You can prefer as you wish.

There are advantages and disadvantages in both cases:
- bool is using less space and limited to only needed part but mistakes
can happen and some will forget to add this line.
- int part is good only if it is not optional.

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