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

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Message-ID: <20240920163851.GA385919@e130802.arm.com>
Date: Fri, 20 Sep 2024 17:38:51 +0100
From: Abdellatif El Khlifi <abdellatif.elkhlifi@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>
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

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.

The external system registers (described by the remoteproc node) are part
of the parent device (the Host Base System Control register area) described
by syscon.

In case of the external system 0 , its registers are located at offset 0x310
(physical address: 0x1a010310)

When instantiating the devices without @address, the DTC compiler
detects 2 nodes with the same name (remoteproc).

syscon@...10000 {
    ...

    remoteproc {
        compatible = "arm,sse710-extsys0";
        ...
    }

    remoteproc {
        compatible = "arm,sse710-extsys1";
        ...
    }

Cheers
Abdellatif