linux-kernel - Re: [PATCH v2 1/5] dt-bindings: remoteproc: sse710: Add the External Systems remote processors

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Message-ID: <7784248d-4372-4cf1-a01a-5b731b3f6b96@kernel.org>
Date: Fri, 20 Sep 2024 16:56:24 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Abdellatif El Khlifi <abdellatif.elkhlifi@....com>
Cc: mathieu.poirier@...aro.org, Adam.Johnston@....com,
 Hugues.KambaMpiana@....com, Drew.Reed@....com, andersson@...nel.org,
 conor+dt@...nel.org, devicetree@...r.kernel.org,
 krzysztof.kozlowski+dt@...aro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
 liviu.dudau@....com, lpieralisi@...nel.org, robh@...nel.org,
 sudeep.holla@....com, robin.murphy@....com
Subject: Re: [PATCH v2 1/5] dt-bindings: remoteproc: sse710: Add the External
 Systems remote processors

On 20/09/2024 16:19, Abdellatif El Khlifi wrote:
> Hi Krzysztof,
> 
>>>>>>> +  '#extsys-id':
>>>>>>
>>>>>> '#' is not correct for sure, that's not a cell specifier.
>>>>>>
>>>>>> But anyway, we do not accept in general instance IDs.
>>>>>
>>>>> I'm happy to replace the instance ID with  another solution.
>>>>> In our case the remoteproc instance does not have a base address
>>>>> to use. So, we can't put remoteproc@...ress
>>>>>
>>>>> What do you recommend in this case please ?
>>>>
>>>> Waiting one month to respond is a great way to drop all context from my
>>>> memory. The emails are not even available for me - gone from inbox.
>>>>
>>>> Bus addressing could note it. Or you have different devices, so
>>>> different compatibles. Tricky to say, because you did not describe the
>>>> hardware really and it's one month later...
>>>>
>>>
>>> Sorry for waiting. I was in holidays.
>>>
>>> I'll add more documentation about the external system for more clarity [1].
>>>
>>> Basically, Linux runs on the Cortex-A35. The External system is a
>>> Cortex-M core. The Cortex-A35 can not access the memory of the Cortex-M.
>>> It can only control Cortex-M core using the reset control and status registers mapped
>>> in the memory space of the Cortex-A35.
>>
>> That's pretty standard.
>>
>> It does not explain me why bus addressing or different compatible are
>> not sufficient here.
> 
> Using an instance ID was a design choice.
> I'm happy to replace it with the use of compatible and match data (WIP).
> 
> The match data will be pointing to a data structure containing the right offsets
> to be used with regmap APIs.
> 
> syscon node is used to represent the Host Base System Control register area [1]
> where the external system reset registers are mapped (EXT_SYS*).
> 
> The nodes will look like this:
> 
> syscon@...10000 {
>         compatible = "arm,sse710-host-base-sysctrl", "simple-mfd", "syscon";
>         reg = <0x1a010000 0x1000>;
> 
>         #address-cells = <1>;
>         #size-cells = <1>;
> 
>         remoteproc@310 {
>             compatible = "arm,sse710-extsys0";
>             reg = <0x310 4>;

Uh, why do you create device nodes for one word? This really suggests it
is part of parent device and your split is artificial.

Best regards,
Krzysztof