Re: [RFC PATCH 2/5] DT: mailbox: add binding doc for the ARM SMC mailbox
From: Rob Herring <hidden>
Date: 2016-08-10 21:57:06
Also in:
linux-arm-kernel, lkml
On Tue, Aug 09, 2016 at 12:53:00PM +0100, Andre Przywara wrote:
quoted hunk ↗ jump to hunk
Signed-off-by: Andre Przywara <redacted> --- .../devicetree/bindings/mailbox/arm-smc.txt | 53 ++++++++++++++++++++++ 1 file changed, 53 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..9919a12 --- /dev/null +++ b/Documentation/devicetree/bindings/mailbox/arm-smc.txt@@ -0,0 +1,53 @@ +ARM SMC Mailbox Driver +====================== + +This mailbox driver uses the ARM smc (secure monitor call) instruction to +trigger a mailbox-connected activity in firmware running on the very same +core as the caller. By nature this operation is synchronous and this +driver provides no way for asynchronous messages to be delivered the other +way round, from firmware to the OS. However the value of r0/w0 the firmware +returns after the smc call is delivered as a received message to the +mailbox framework, so a synchronous communication can be established.
Clever
+ +One usecase of this mailbox is the SCP interface, which uses shared memory +to transfer commands and parameters and mailboxes to trigger a function +call. This driver allows SoC without a separate management processor (or +when such a processor is not available or used) to use this standardized +interface anyway. + +The driver requires no special hardware, any core which supports the SMC +instruction can be used. This requires firmware in monitor mode/EL3 to +handle the mailbox message. + +Mailbox Device Node: +==================== + +Required properties: +-------------------- +- compatible: Shall be "arm,smc-mbox" +- #mbox-cells Shall be 1 - the index of the channel needed. +- identifiers An array of 32-bit values specifying the function
Minimally, needs 'arm' prefix. 'identifiers' is pretty vague. Perhaps 'arm,smc-func-ids' to say exactly what they are.
+ 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.
+
+Example:
+--------
+
+ mailbox: smc_mbox {
+ #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
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