linux-kernel - Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

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Message-ID: <CAL_JsqJK9Wkr-x2RbgGfqSDfK7b21MQAaWwONfVwQV8eHAm+qg@mail.gmail.com>
Date:   Fri, 9 Jun 2017 10:39:39 -0500
From:   Rob Herring <robh@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Roy Franz <roy.franz@...ium.com>,
        Harb Abdulhamid <harba@...eaurora.org>,
        Nishanth Menon <nm@...com>, Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System
 Control and Management Interface(SCMI) protocol

On Fri, Jun 9, 2017 at 9:47 AM, Sudeep Holla <sudeep.holla@....com> wrote:
>
>
> On 09/06/17 15:16, Rob Herring wrote:
>> On Wed, Jun 07, 2017 at 05:10:05PM +0100, Sudeep Holla wrote:
>>> This patch adds devicetree binding for System Control and Management
>>> Interface (SCMI) Message Protocol used between the Application Cores(AP)
>>> and the System Control Processor(SCP). The MHU peripheral provides a
>>> mechanism for inter-processor communication between SCP's M3 processor
>>> and AP.
>>>
>>> SCP offers control and management of the core/cluster power states,
>>> various power domain DVFS including the core/cluster, certain system
>>> clocks configuration, thermal sensors and many others.
>>>
>>> SCMI protocol is developed as better replacement to the existing SCPI
>>> which is not flexible and easily extensible.
>>>
>>> Cc: Rob Herring <robh+dt@...nel.org>
>>> Cc: Mark Rutland <mark.rutland@....com>
>>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
>>> ---
>>>  Documentation/devicetree/bindings/arm/arm,scmi.txt | 193 +++++++++++++++++++++
>>>  1 file changed, 193 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/arm/arm,scmi.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/arm/arm,scmi.txt b/Documentation/devicetree/bindings/arm/arm,scmi.txt
>>> new file mode 100644
>>> index 000000000000..d6e4b7eff199
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/arm/arm,scmi.txt
>>> @@ -0,0 +1,193 @@
>>> +System Control and Management Interface (SCMI) Message Protocol
>>> +----------------------------------------------------------
>>> +
>>> +The SCMI is intended to allow agents such as OSPM to manage various functions
>>> +that are provided by the hardware platform it is running on, including power
>>> +and performance functions.
>>> +
>>> +This binding is intended to define the interface the firmware implementing
>>> +the SCMI as described in ARM document number ARM DUI 0922B ("ARM System Control
>>> +and Management Interface Platform Design Document")[0] provide for OSPM in
>>> +the device tree.
>>> +
>>> +Required properties:
>>> +
>>> +- compatible : shall be "arm,scmi"
>>
>> Convince me that this genericish string is specific enough.
>>
>
> Now that you raised this point, I think we generate so many 4 letter
> acronyms that it can collide. How about "arm,sys-ctl-mgmt-if"

I was more concerned about needing versioning or vendor specific
compatible strings that we needed with SCPI. Is there a spec version
or is that discoverable?

>>> +- method : The method of calling the SCMI firmware. Only permitted value
>>> +       currently is:
>>> +       "mailbox-doorbell" : When mailbox doorbell is used as a mechanism
>>> +                            to alert the presence of a messages and/or
>>> +                            notification
>>> +- mboxes: List of phandle and mailbox channel specifiers. It should contain
>>> +      exactly one or two mailboxes, one for transmitting messages("tx")
>>> +      and another optional for receiving the notifications("rx") if
>>> +      supported.
>>> +- mbox-names: shall be "tx" or "rx"
>>
>> ...and optionally "rx"
>>
>
> OK
>
>>> +- shmem : List of phandle pointing to the shared memory(SHM) area between the
>>> +      processors using these mailboxes for IPC, one for each mailbox
>>> +      SHM can be any memory reserved for the purpose of this communication
>>> +      between the processors.
>>
>> Maybe the mailbox binding should have a standard property for this?
>>
>
> Do you mean as part of it's client binding ? If so, agreed. I can come
> up with that proposal.

Yes.

Rob