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