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

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  [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol Sudeep Holla <sudeep.holla@arm.com> - 2017-06-07 18:20 +0200
    Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System  Control and Management Interface(SCMI) protocol Rob Herring <robh@kernel.org> - 2017-06-09 16:20 +0200
      Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System  Control and Management Interface(SCMI) protocol Sudeep Holla <sudeep.holla@arm.com> - 2017-06-09 16:50 +0200
        Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System  Control and Management Interface(SCMI) protocol Rob Herring <robh@kernel.org> - 2017-06-09 17:50 +0200
          Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System  Control and Management Interface(SCMI) protocol Sudeep Holla <sudeep.holla@arm.com> - 2017-06-09 18:00 +0200
    Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System  Control and Management Interface(SCMI) protocol Sudeep Holla <sudeep.holla@arm.com> - 2017-06-12 19:40 +0200

#1659972 — [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

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@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.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"
+- 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"
+- 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.
+
+See Documentation/devicetree/bindings/mailbox/mailbox.txt for more details
+about the generic mailbox controller and client driver bindings.
+
+Each protocol supported shall have a sub-node with corresponding compatible
+as described in the following sections. If the platform supports dedicated
+communication channel for a particular protocol, the 3 properties namely:
+mboxes, mbox-names and shmem shall be present in the sub-node corresponding
+to that protocol.
+
+Clock/Performance bindings for the clocks/OPPs based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding uses the common clock binding[1].
+
+Required properties:
+- compatible : shall be "arm,scmi-clocks" or "arm,scmi-perf-domains"
+	arm,scmi-clocks:
+	       These clocks either provide an entire range of values
+	       between the limits or only discrete points each at fixed
+	       step size between the limits. The firmware provides
+	       mechanism to discover them.
+	arm,scmi-perf-domains:
+		These are OPPs(not just simple clocks), i.e. discrete
+		performance levels that are supported by the platform.
+		Again the firmware provides mechanism to discover the
+		performance and other attributes associated with the
+		levels.
+
+Other required properties for all clocks(all from common clock binding):
+- #clock-cells : Should be 1. Contains the Clock ID value used by SCMI commands.
+- clock-indices: The identifying number for the clocks(i.e.clock_id) in the
+	node. It can be non linear and hence provide the mapping of
+	identifiers.
+
+Power domain bindings for the power domains based on SCMI Message Protocol
+------------------------------------------------------------
+
+This binding uses the generic power domain binding[4].
+
+PM domain providers
+===================
+
+Required properties:
+ - #power-domain-cells : Should be 1. Contains the device or the power
+			 domain ID value used by SCMI commands.
+
+PM domain consumers
+===================
+
+Required properties:
+ - power-domains : A phandle and PM domain specifier as defined by bindings of
+                   the power controller specified by phandle.
+
+Sensor bindings for the sensors based on SCMI Message Protocol
+--------------------------------------------------------------
+SCMI provides an API to access the various sensors on the SoC.
+
+Required properties:
+- compatible : should be "arm,scmi-sensors".
+- #thermal-sensor-cells: should be set to 1. This property follows the
+			 thermal device tree bindings[2].
+
+			 Valid cell values are raw identifiers (Sensor ID)
+			 as used by the firmware. Refer to  platform details
+			 for your implementation for the IDs to use.
+
+SRAM and Shared Memory for SCMI
+-------------------------------
+
+A small area of SRAM is reserved for SCMI communication between application
+processors and SCP.
+
+The properties should follow the generic mmio-sram description found in [3]
+
+Each sub-node represents the reserved area for SCMI.
+
+Required sub-node properties:
+- reg : The base offset and size of the reserved area with the SRAM
+- compatible : should be "arm,scp-shmem" for Non-secure SRAM based
+	       shared memory
+
+[0] http://infocenter.arm.com/help/topic/com.arm.doc.den0056a/index.html
+[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
+[2] Documentation/devicetree/bindings/thermal/thermal.txt
+[3] Documentation/devicetree/bindings/sram/sram.txt
+[4] Documentation/devicetree/bindings/power/power_domain.txt
+
+Example:
+
+sram: sram@50000000 {
+	compatible = "arm,juno-sram-ns", "mmio-sram";
+	reg = <0x0 0x50000000 0x0 0x10000>;
+
+	#address-cells = <1>;
+	#size-cells = <1>;
+	ranges = <0 0x0 0x50000000 0x10000>;
+
+	cpu_scp_lpri: scp-shmem@0 {
+		compatible = "arm,juno-scp-shmem";
+		reg = <0x0 0x200>;
+	};
+
+	cpu_scp_hpri: scp-shmem@200 {
+		compatible = "arm,juno-scp-shmem";
+		reg = <0x200 0x200>;
+	};
+};
+
+mailbox: mailbox0@40000000 {
+	....
+	#mbox-cells = <1>;
+};
+
+scmi_protocol: scmi@2e000000 {
+	compatible = "arm,scmi";
+	mboxes = <&mailbox 0 &mailbox 1>;
+	shmem = <&cpu_scp_lpri &cpu_scp_hpri>;
+
+	scmi_dvfs: clocks@0 {
+		compatible = "arm,scmi-perf-domains";
+		#clock-cells = <1>;
+		clock-indices = <0>, <1>, <2>;
+	};
+	scmi_clk: clocks@3 {
+		compatible = "arm,scmi-clocks";
+		#clock-cells = <1>;
+		clock-indices = <3>, <4>;
+	};
+
+	scmi_sensors: sensors {
+		compatible = "arm,scmi-sensors";
+		#thermal-sensor-cells = <1>;
+	};
+
+	scmi_devpd: power-domains {
+		compatible = "arm,scmi-power-domains";
+		#power-domain-cells = <1>;
+	};
+};
+
+cpu@0 {
+	...
+	reg = <0 0>;
+	clocks = <&scmi_dvfs 0>;
+};
+
+hdlcd@7ff60000 {
+	...
+	reg = <0 0x7ff60000 0 0x1000>;
+	clocks = <&scmi_clk 4>;
+	power-domains = <&scmi_devpd 1>;
+};
+
+thermal-zones {
+	soc_thermal {
+		polling-delay-passive = <100>;
+		polling-delay = <1000>;
+
+				/* sensor         ID */
+		thermal-sensors = <&scmi_sensors0 3>;
+		...
+	};
+};
-- 
2.7.4

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#1662493 — Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

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@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.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.

> +- 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"

> +- 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?

> +
> +See Documentation/devicetree/bindings/mailbox/mailbox.txt for more details
> +about the generic mailbox controller and client driver bindings.
> +
> +Each protocol supported shall have a sub-node with corresponding compatible
> +as described in the following sections. If the platform supports dedicated
> +communication channel for a particular protocol, the 3 properties namely:
> +mboxes, mbox-names and shmem shall be present in the sub-node corresponding
> +to that protocol.
> +
> +Clock/Performance bindings for the clocks/OPPs based on SCMI Message Protocol
> +------------------------------------------------------------
> +
> +This binding uses the common clock binding[1].
> +
> +Required properties:
> +- compatible : shall be "arm,scmi-clocks" or "arm,scmi-perf-domains"
> +	arm,scmi-clocks:
> +	       These clocks either provide an entire range of values
> +	       between the limits or only discrete points each at fixed
> +	       step size between the limits. The firmware provides
> +	       mechanism to discover them.
> +	arm,scmi-perf-domains:
> +		These are OPPs(not just simple clocks), i.e. discrete
> +		performance levels that are supported by the platform.
> +		Again the firmware provides mechanism to discover the
> +		performance and other attributes associated with the
> +		levels.
> +
> +Other required properties for all clocks(all from common clock binding):
> +- #clock-cells : Should be 1. Contains the Clock ID value used by SCMI commands.
> +- clock-indices: The identifying number for the clocks(i.e.clock_id) in the
> +	node. It can be non linear and hence provide the mapping of
> +	identifiers.
> +
> +Power domain bindings for the power domains based on SCMI Message Protocol
> +------------------------------------------------------------
> +
> +This binding uses the generic power domain binding[4].
> +
> +PM domain providers
> +===================
> +
> +Required properties:
> + - #power-domain-cells : Should be 1. Contains the device or the power
> +			 domain ID value used by SCMI commands.
> +
> +PM domain consumers
> +===================
> +
> +Required properties:
> + - power-domains : A phandle and PM domain specifier as defined by bindings of
> +                   the power controller specified by phandle.
> +
> +Sensor bindings for the sensors based on SCMI Message Protocol
> +--------------------------------------------------------------
> +SCMI provides an API to access the various sensors on the SoC.
> +
> +Required properties:
> +- compatible : should be "arm,scmi-sensors".
> +- #thermal-sensor-cells: should be set to 1. This property follows the
> +			 thermal device tree bindings[2].
> +
> +			 Valid cell values are raw identifiers (Sensor ID)
> +			 as used by the firmware. Refer to  platform details
> +			 for your implementation for the IDs to use.
> +
> +SRAM and Shared Memory for SCMI
> +-------------------------------
> +
> +A small area of SRAM is reserved for SCMI communication between application
> +processors and SCP.
> +
> +The properties should follow the generic mmio-sram description found in [3]
> +
> +Each sub-node represents the reserved area for SCMI.
> +
> +Required sub-node properties:
> +- reg : The base offset and size of the reserved area with the SRAM
> +- compatible : should be "arm,scp-shmem" for Non-secure SRAM based
> +	       shared memory
> +
> +[0] http://infocenter.arm.com/help/topic/com.arm.doc.den0056a/index.html
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +[2] Documentation/devicetree/bindings/thermal/thermal.txt
> +[3] Documentation/devicetree/bindings/sram/sram.txt
> +[4] Documentation/devicetree/bindings/power/power_domain.txt
> +
> +Example:
> +
> +sram: sram@50000000 {
> +	compatible = "arm,juno-sram-ns", "mmio-sram";
> +	reg = <0x0 0x50000000 0x0 0x10000>;
> +
> +	#address-cells = <1>;
> +	#size-cells = <1>;
> +	ranges = <0 0x0 0x50000000 0x10000>;
> +
> +	cpu_scp_lpri: scp-shmem@0 {
> +		compatible = "arm,juno-scp-shmem";
> +		reg = <0x0 0x200>;
> +	};
> +
> +	cpu_scp_hpri: scp-shmem@200 {
> +		compatible = "arm,juno-scp-shmem";
> +		reg = <0x200 0x200>;
> +	};
> +};
> +
> +mailbox: mailbox0@40000000 {
> +	....
> +	#mbox-cells = <1>;
> +};
> +
> +scmi_protocol: scmi@2e000000 {
> +	compatible = "arm,scmi";
> +	mboxes = <&mailbox 0 &mailbox 1>;
> +	shmem = <&cpu_scp_lpri &cpu_scp_hpri>;
> +
> +	scmi_dvfs: clocks@0 {
> +		compatible = "arm,scmi-perf-domains";
> +		#clock-cells = <1>;
> +		clock-indices = <0>, <1>, <2>;
> +	};
> +	scmi_clk: clocks@3 {
> +		compatible = "arm,scmi-clocks";
> +		#clock-cells = <1>;
> +		clock-indices = <3>, <4>;
> +	};
> +
> +	scmi_sensors: sensors {
> +		compatible = "arm,scmi-sensors";
> +		#thermal-sensor-cells = <1>;
> +	};
> +
> +	scmi_devpd: power-domains {
> +		compatible = "arm,scmi-power-domains";
> +		#power-domain-cells = <1>;
> +	};
> +};
> +
> +cpu@0 {
> +	...
> +	reg = <0 0>;
> +	clocks = <&scmi_dvfs 0>;
> +};
> +
> +hdlcd@7ff60000 {
> +	...
> +	reg = <0 0x7ff60000 0 0x1000>;
> +	clocks = <&scmi_clk 4>;
> +	power-domains = <&scmi_devpd 1>;
> +};
> +
> +thermal-zones {
> +	soc_thermal {
> +		polling-delay-passive = <100>;
> +		polling-delay = <1000>;
> +
> +				/* sensor         ID */
> +		thermal-sensors = <&scmi_sensors0 3>;
> +		...
> +	};
> +};
> -- 
> 2.7.4
> 

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#1662531 — 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@kernel.org>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.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

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#1662572 — 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@arm.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@kernel.org>
>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.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

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#1662575 — Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

On 09/06/17 16:39, Rob Herring wrote:
> On Fri, Jun 9, 2017 at 9:47 AM, Sudeep Holla <sudeep.holla@arm.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@kernel.org>
>>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.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?
> 

Ah ok, it's discoverable and each protocol must implement
PROTOCOL_VERSION. We have specification version implemented, vendor id
and firmware implementation version all of which is mandatory.

>>>> +- 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.

Thanks, will do.

-- 
Regards,
Sudeep

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#1664110 — Re: [RFC PATCH 1/8] Documentation: add DT binding for ARM System Control and Management Interface(SCMI) protocol

Hi Matt,


Thanks for starting this discussion on the list.

On Fri, Jun 09, 2017 at 01:12:50PM -0500, Matt Sealey wrote:
> Hullo all,
> 
> This is a long one.. apologies for odd linefeeds and so on.
> 
> On Wed, Jun 7, 2017 at 11:10 AM, Sudeep Holla <sudeep.holla@arm.com> wrote:
> 
> > +Clock/Performance bindings for the clocks/OPPs based on SCMI Message
> Protocol
> > +------------------------------------------------------------
> > +
> > +This binding uses the common clock binding[1].
> > +
> > +Required properties:
> > +- compatible : shall be "arm,scmi-clocks" or "arm,scmi-perf-domains"
> 
> After a little thought, there are a couple objections to be made here.
> Firstly, the SCMI protocol families are  discoverable - you only really need
> to know that it is usable (and where to use it, mboxes etc.) - whether it
> supports the clock management, performance domains, power domains et al.
> protocols is a function of querying the base protocol for a list.
>
> These protocols are identified by a value, several of which are
> standardized, some being vendor extension numbers. All protocols must be
> able to be queried for information.
>

Agreed on most the above.

> As such, defining compatible properties for each protocol is treading that
> fine line of tying device trees to particular driver subsystems and giving
> operating systems an ability to ignore any discovery procedure. While I
> can't make a case for clock management (which should obviously conform with
> a particular clock management definition in DT, as already defined), there
> is plenty of past evidence of bindings for particular devices being mis-used
> or used in non-intended ways (regulators as reset GPIOs is the one that
> immediately came to mind) in lieu of a more fleshed out way of defining a
> particular class of device for a binding. The same would be true of tying a
> 'performance domain' to the concept of clock management.
>

As I mentioned in private, I reused clock for simplicity and most of the
platforms already do that. But yes, that's no valid argument to just
continue the legacy. I am fine to break clock and performance domains.
The main problem IMO is that it's not well defined either in theis
specification or architecture to an extent that we can define a standard
binding and live with it. We are/already have seen lost of churn around
this bindings and that's one of the reason I chose to reuse existing
bindings.

> From the point of view of being able to specify things against a particular
> binding (whatever that might be), one could imagine something that mapped
> protocols to those bindings without introducing compatible names. SCMI ids
> would be verbatim, and per-protocol. Things like clock-indices are therefore
> not relevant and defining which indices go with which protocol at the SCMI
> level isn't needed anymore. It is really up to the protocol how many cells
> it would need to define it's protocol behavior but for the purpose of some
> standardization, we could imagine a binding that defined protocols as such:
> 
> scmi: arm_scmi {
>         compatible = "arm,scmi,1.0";

I prefer v1.0 dropped based on the same argument that it's discoverable.
If we don't agree on that then the whole discussion falls apart. I
assume you agree on dropping versioning just to continue the discussion
here.

>         mboxes = <y>;
>         shmem = <x>;
>         protocols {
>               scmi_clocks: protocol@0x14 {
>                         #whatever-cells = 3;
>                };
>                foo_smic: protocol@0x89 {
>                         #foo-cells = 4;
>                         #bar-cells = 5;
>                 };
>         };
> };
> 
> uart: myuart@80000000 {
>         compatible = "arm,pl011";
>         clocks = <&foo_smic 3>;
> };
> 
> If you manage to get a device tree that specifies a clock but there is no
> protocol 0x89 then you're just as hosed as if you specified an
> arm,scmi-clocks node when the protocol was not supported by SCMI itself, so
> we don't gain any new dangers, but we do gain the ability to instantiate
> SCMI, discover protocols, and then load drivers against those protocols,
> without duplicating the discovery process with a hardcoded tree. Device
> trees, from my point of view, are a contract between the SoC & board
> designer and the OS (helped along by firmware, hopefully). They shouldn't be
> dictating the driver behavior to be applied at this kind of level. 

Agreed.

> Device trees need to be rock solid - agile development is fine but as soon
> as you ship, changing the device tree means cutting off support for existing
> software, or only working with augmented features on new software and
> severely reduced functionality on old software. That can be as simple as not
> being able to go to Turbo mode, or as bad as an inability to apply thermal
> limits and burning someone's board. If we define a specific binding of a
> specific protocol to a specific way of interacting with that device which is
> a purely software construct (like treating performance domain as an abstract
> clock interface with a particular number of cells or clock-like behavior),
> then you lock down protocols to *existing* OS subsystems. That means
> maintaining that subsystem and device tree specification to retain behavior,
> which is a lot of maintaining.

In total agreement with you.

> It shouldn't be necessary to actually define which protocols exist and what
> number of cells they use in the device tree binding, because this is
> actually documented elsewhere. Just as we do not create compatible
> properties for new devices which work the same as old ones, or redefine
> features which would otherwise be ascertained by some kind of discovery (PCI
> devices, USB devices, but even as simple just reading out an ID register
> from a device to determine if it has a particular feature), we shouldn't do
> this to lock down a further discovery model for activity types or
> programmers' models under those protocols.

Reasonable.

> Here's where I fall down: with a variable number of cells per protocol
> required (potentially) and no method to be able to assign a particular
> protocol's device or functionality to something else, discovery of what maps
> where has to be done as well. There's little of that in SCMI, that is to say
> it wouldn't be possible to infer that clock_id 20 in protocol 0x14 is the
> clock that goes with cpu@0. It is also, per the SCMI spec, a firmware table
> responsibility to define any dependencies on other parts of the protocol
> (for instance, clock trees). The best I can think of right now is that this
> would just have to be done on a global SCMI level:

> 
> scmi: arm_scmi {
>         compatible = "arm,scmi,1.0";
>         mboxes = <y>;
>         shmem = <x>;
>         disable-protocols = <0x87, 0x88>;
>	  // these are buggy, don't load drivers even if they're implemented
> 
>         #whatever-cells = 3;
>         required-whatever-prop;
> 
>         #foo-cells = 4;
> 
>         #bar-cells = 5;
>         optional-bar-prop = <5, 10, 15>;
> 
>         #clock-cells = 10;
> };
> 
> #define SCMI_PROTO_CLOCKMGMT 0x14
> #define SCMI_PROTO_VENDOR_CLOCKS 0x89
> uart: myuart {
>         compatible = "arm,pl011";
>         clocks = <&scmi SCMI_PROTO_CLOCKMGMT 3 0 0 0 0 0 0 0 0>, <&scmi
> SCMIU_PROTO_VENDOR_CLOCKS 3 4 7 99 0 0 0x9000 3>;
> };
> 

OK, I really don't like this. But if other's think this is better, then
I am fine with that. I prefer the first option you have present.

IMO we might collide with the property name soon i.e. 2 different
existing bindings having same property name.

> .. it is up to the driver to figure out what exactly this does in real
> life, without having to lock it to the clock et al. binding, but at least
> all drivers using protocols must be able to parse the number of cells
> defined. If a protocol only needs 3 cells, but another needs 10 cells for
> the same thing, then both protocols will by definition be defined as 10-cell
> groups. It implies hat any device that can be controlled or affected by SCMI
> can list the devices, and the protocol driver will be required to parse the
> remaining cells and ignore them. As long as the device tree can cover all
> cases in it's #foo-cells or other binding properties, it would be most
> flexible here.
>
> I don't like the lockdown of having to cover every binding that gets used
> whether it's truly for that device type or not, but it would be the most
> flexible within the current framework, without defeating discovery.

Sounds good, but as I said I am worried if we collide.

> We would do well to come up with a way of defining abstract interfaces to
> firmware or other processors that don't rely on there being a fixed binding
> that dictates what kind of device it is, where there isn't a way of defining
> that device type in a generic manner. There's no way of doing this right now
> and letting the driver in the OS know what's necessary - well, there is,
> things like RTAS support on CHRP got away with this in the old days, and
> PSCI does something very similar (which covers quite a lot of CPU management
> and also system domain activity), so it's not like we've come up against the
> issue before. But it's not been resolved when a device node would need to
> refer back to those abstraction interface nodes where there's not a
> reasonable way of binding the definition of the reference.

Exactly, I am trying to reuse existing bindings with minimum change to
provide the glue to SCMI interface. But I am open for any suggestions.

> RTAS had a property in every device node that depended on it and would be
> affected by it, "used-by-rtas". Perhaps we could augment devices with an
> "managed-by" property likewise to point to the protocol node.
> #protocol-cells might be a nice way of defining cell sizes generically
> (where protocol would be the name of the protocol - #scmi-cells perhaps -
> and the format of #scmi-cells would need to include the protocol number).
> Wrapping that up in a generic binding means each protocol then gets control
> of it's own world, and each device that is affected by that protocol would
> be able to realize this.

Interesting, I need more opinions here.

> If anyone comes up with a particular PSCI-like protocol for anything here
> that kind of adaptable binding for device/platform abstraction frameworks
> with non-discrete methods of working (i.e. it might not be able to be
> defined as "just a clock" or "just a power domain" or "just a thermal
> framework" or any combination without reducing functionality that would
> otherwise come from some built-in discovery system) would come in very
> handy.
>
> Just thoughts right now, though. I definitely don't have the whole story
> down, but it is definitely something to think about.

Sure, thanks again for such a detailed mail. Hope to see more
discussions if we need to make such drastic changes.

-- 
Regards,
Sudeep

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