Re: [PATCH v7 4/6] dt-bindings: mailbox: imx-mu: add i.MX6SX and i.MX7S SoCs.

[Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>]

On 07/26/2018 02:15 PM, Jassi Brar wrote:
> On Thu, Jul 26, 2018 at 4:11 PM, Lucas Stach <l.stach@pengutronix.de> wrote:
>> Hi Jassi,
>>
>> Am Donnerstag, den 26.07.2018, 15:25 +0530 schrieb Jassi Brar:
>>> On Thu, Jul 26, 2018 at 12:23 PM, Oleksij Rempel
>>>> <o.rempel@pengutronix.de> wrote:
>>>> This are currently tested SoCs with imx-mailbox driver.
>>>>
>>>>>> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
>>>> ---
>>>>  Documentation/devicetree/bindings/mailbox/fsl,mu.txt | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mailbox/fsl,mu.txt b/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>> index 113d6ab931ef..5616d2afca45 100644
>>>> --- a/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>> +++ b/Documentation/devicetree/bindings/mailbox/fsl,mu.txt
>>>> @@ -18,7 +18,7 @@ Messaging Unit Device Node:
>>>>  Required properties:
>>>>  -------------------
>>>>  - compatible : should be "fsl,<chip>-mu", the supported chips include
>>>> -               imx8qxp, imx8qm.
>>>> +               imx6sx, imx7s, imx8qxp, imx8qm.
>>>>
>>>
>>> This is not scalable. Do we add every new SoC that contains the same controller?
>>
>> Yes, we do. This is a policy direction from the DT maintainers.
>>
> I would love to read the post/documentation.

Some notes are found in Documentation/devicetree/bindings/ABI.txt

To guarantee "a stable binding" of a compatible property, to avoid
unintentionally added incompatibilities and to fix a list of supported
compatibles in the device driver code there should be a SoC specific
compatible value in the list of 'compatible' property elements.

> Consider the same h/w - controller and platforms, but only the the MU
> chapter said the controller name is, say, 'MU121'. I am sure now you
> will see it correct to call it "fsl,mu121" compatible.
> What changed? just the name, right?
> 
> 
>> If we
>> ever going to want to validate DTs against the binding, all compatibles
>> used in the DTs must be specified in the binding.
>>
>> As we can't really tell if the controller is exactly the same or even
>> has some SoC integration bugs, we generally add a new compatible for
>> each SoC to key off any workarounds necessary in the driver without the
>> need to change the DTs, breaking compatibility.
>>
> I think if the h/w resources and behaviour remain the same and the
> documentation does not call it by a different name -- it is safe to
> assume its the same IP. Especially when the driver is absolutely
> indifferent to the 5 SoC names.
> 
> If/when we find the controller changes, we could revisit the binding
> and add another compatible option and modify the driver to catch that
> and adapt.
> 

Unfortunately it does not work well this way due to limited possibilities
to distinugush different device IPs on different SoCs, if identical
compatibles are given in both cases, and often it is not obvious that
two IPs are different.

--
Best wishes,
Vladimir