[PATCH 2/8] dt-bindings: mailbox: add binding doc for the ARM SMC mailbox
From: robh@kernel.org (Rob Herring)
Date: 2017-07-07 13:53:30
Also in:
linux-devicetree, lkml
On Fri, Jun 30, 2017 at 10:56:02AM +0100, Andre Przywara wrote:
quoted hunk ↗ jump to hunk
Add binding documentation for the generic ARM SMC mailbox. This is not describing hardware, but a firmware interface. Signed-off-by: Andre Przywara <andre.przywara@arm.com> --- .../devicetree/bindings/mailbox/arm-smc.txt | 61 ++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txtdiff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.txt b/Documentation/devicetree/bindings/mailbox/arm-smc.txt new file mode 100644 index 0000000..90c5926 --- /dev/null +++ b/Documentation/devicetree/bindings/mailbox/arm-smc.txt@@ -0,0 +1,61 @@ +ARM SMC Mailbox Driver
s/Driver/Interface/
+====================== + +This mailbox uses the ARM smc (secure monitor call) instruction to +trigger a mailbox-connected activity in firmware, executing on the very same +core as the caller. By nature this operation is synchronous and this +mailbox provides no way for asynchronous messages to be delivered the other +way round, from firmware to the OS. However the value of r0/w0/x0 the firmware +returns after the smc call is delivered as a received message to the +mailbox framework, so a synchronous communication can be established. + +One use case of this mailbox is the SCP interface, which uses shared memory +to transfer commands and parameters, and a mailbox to trigger a function +call. This allows SoCs without a separate management processor (or +when such a processor is not available or used) to use this standardized +interface anyway. + +This binding describes no hardware, but establishes a firmware interface. +The communication follows the ARM SMC calling convention[1]. +Any core which supports the SMC or HVC instruction can be used, as long as +a firmware component running in EL3 or EL2 is handling these calls. + +Mailbox Device Node: +====================
Please state this should be a child of /firmware node.
+
+Required properties:
+--------------------
+- compatible: Shall be "arm,smc-mbox"
+- #mbox-cells Shall be 1 - the index of the channel needed.
+- arm,smc-func-ids An array of 32-bit values specifying the function
+ IDs used by each mailbox channel. Those function IDs
+ follow the ARM SMC calling convention standard [1].
+ There is one identifier per channel and the number
+ of supported channels is determined by the length
+ of this array.
+
+Optional properties:
+--------------------
+- method: A string, either:
+ "hvc": if the driver shall use an HVC call, or
+ "smc": if the driver shall use an SMC call
+ If omitted, defaults to an SMC call.
+
+Example:
+--------
+
+ mailbox: smc_mbox {swap these. mailbox for the node name.
+ #mbox-cells = <1>;
+ compatible = "arm,smc-mbox";
+ identifiers = <0x82000001>, <0x82000002>;
+ };
+
+ scpi {
+ compatible = "arm,scpi";
+ mboxes = <&mailbox 0>;
+ shmem = <&cpu_scp_shmem>;
+ };
+
+
+[1]
+http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0028a/index.html
--
2.9.0