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: <8d17f317-510c-b98e-4c42-c4ad2a8f0c63@arm.com>
Date:   Fri, 9 Jun 2017 15:47:59 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Rob Herring <robh@...nel.org>
Cc:     Sudeep Holla <sudeep.holla@....com>, linux-kernel@...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 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"

>> +- 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.

-- 
Regards,
Sudeep