[PATCH v3 1/2] dt-bindings: mailbox: arm,mhuv3: Add bindings

Cristian Marussi
2024-04-04T06:25:17Z

Add bindings for the ARM MHUv3 Mailbox controller.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v2 -> v3
- fixed spurious tabs in dt_binding_check
v1 -> v2
- clarified extension descriptions around configurability and discoverability
- removed unused labels from the example
- using pattern properties to define interrupt-names
- bumped interrupt maxItems to 74 (allowing uo to 8 channels per extension)
---
.../bindings/mailbox/arm,mhuv3.yaml | 217 ++++++++++++++++++
1 file changed, 217 insertions(+)
create mode 100644 Documentation/devicetree/bindings/mailbox/arm,mhuv3.yaml

diff --git a/Documentation/devicetree/bindings/mailbox/arm,mhuv3.yaml b/Documentation/devicetree/bindings/mailbox/arm,mhuv3.yaml
new file mode 100644
index 000000000000..32a8bb711464
--- /dev/null
+++ b/Documentation/devicetree/bindings/mailbox/arm,mhuv3.yaml
@@ -0,0 +1,217 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/arm,mhuv3.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ARM MHUv3 Mailbox Controller
+
+maintainers:
+ - Sudeep Holla <sudeep.holla@arm.com>
+ - Cristian Marussi <cristian.marussi@arm.com>
+
+description: |
+ The Arm Message Handling Unit (MHU) Version 3 is a mailbox controller that
+ enables unidirectional communications with remote processors through various
+ possible transport protocols.
+ The controller can optionally support a varying number of extensions that, in
+ turn, enable different kinds of transport to be used for communication.
+ Number, type and characteristics of each supported extension can be discovered
+ dynamically at runtime.
+
+ Given the unidirectional nature of the controller, an MHUv3 mailbox controller
+ is composed of a MHU Sender (MHUS) containing a PostBox (PBX) block and a MHU
+ Receiver (MHUR) containing a MailBox (MBX) block, where
+
+ PBX is used to
+ - Configure the MHU
+ - Send Transfers to the Receiver
+ - Optionally receive acknowledgment of a Transfer from the Receiver
+
+ MBX is used to
+ - Configure the MHU
+ - Receive Transfers from the Sender
+ - Optionally acknowledge Transfers sent by the Sender
+
+ Both PBX and MBX need to be present and defined in the DT description if you
+ need to establish a bidirectional communication, since you will have to
+ acquire two distinct unidirectional channels, one for each block.
+
+ As a consequence both blocks needs to be represented separately and specified
+ as distinct DT nodes in order to properly describe their resources.
+
+ Note that, though, thanks to the runtime discoverability, there is no need to
+ identify the type of blocks with distinct compatibles.
+
+ Following are the MHUv3 possible extensions.
+
+ - Doorbell Extension (DBE): DBE defines a type of channel called a Doorbell
+ Channel (DBCH). DBCH enables a single bit Transfer to be sent from the
+ Sender to Receiver. The Transfer indicates that an event has occurred.
+ When DBE is implemented, the number of DBCHs that an implementation of the
+ MHU can support is between 1 and 128, numbered starting from 0 in ascending
+ order and discoverable at run-time.
+ Each DBCH contains 32 individual fields, referred to as flags, each of which
+ can be used independently. It is possible for the Sender to send multiple
+ Transfers at once using a single DBCH, so long as each Transfer uses
+ a different flag in the DBCH.
+ Optionally, data may be transmitted through an out-of-band shared memory
+ region, wherein the MHU Doorbell is used strictly as an interrupt generation
+ mechanism, but this is out of the scope of these bindings.
+
+ - FastChannel Extension (FCE): FCE defines a type of channel called a Fast
+ Channel (FCH). FCH is intended for lower overhead communication between
+ Sender and Receiver at the expense of determinism. An FCH allows the Sender
+ to update the channel value at any time, regardless of whether the previous
+ value has been seen by the Receiver. When the Receiver reads the channel's
+ content it gets the last value written to the channel.
+ FCH is considered lossy in nature, and means that the Sender has no way of
+ knowing if, or when, the Receiver will act on the Transfer.
+ FCHs are expected to behave as RAM which generates interrupts when writes
+ occur to the locations within the RAM.
+ When FCE is implemented, the number of FCHs that an implementation of the
+ MHU can support is between 1-1024, if the FastChannel word-size is 32-bits,
+ or between 1-512, when the FastChannel word-size is 64-bits.
+ FCHs are numbered from 0 in ascending order.
+ Note that the number of FCHs and the word-size are implementation defined,
+ not configurable but discoverable at run-time.
+ Optionally, data may be transmitted through an out-of-band shared memory
+ region, wherein the MHU FastChannel is used as an interrupt generation
+ mechanism which carries also a pointer to such out-of-band data, but this
+ is out of the scope of these bindings.
+
+ - FIFO Extension (FE): FE defines a Channel type called a FIFO Channel (FFCH).
+ FFCH allows a Sender to send
+ - Multiple Transfers to the Receiver without having to wait for the
+ previous Transfer to be acknowledged by the Receiver, as long as the
+ FIFO has room for the Transfer.
+ - Transfers which require the Receiver to provide acknowledgment.
+ - Transfers which have in-band payload.
+ In all cases, the data is guaranteed to be observed by the Receiver in the
+ same order which the Sender sent it.
+ When FE is implemented, the number of FFCHs that an implementation of the
+ MHU can support is between 1 and 64, numbered starting from 0 in ascending
+ order. The number of FFCHs, their depth (same for all implemented FFCHs) and
+ the access-granularity are implementation defined, not configurable but
+ discoverable at run-time.
+ Optionally, additional data may be transmitted through an out-of-band shared
+ memory region, wherein the MHU FIFO is used to transmit, in order, a small
+ part of the payload (like a header) and a reference to the shared memory
+ area holding the remaining, bigger, chunk of the payload, but this is out of
+ the scope of these bindings.
+
+properties:
+ compatible:
+ const: arm,mhuv3
+
+ reg:
+ maxItems: 1
+
+ interrupts:
+ minItems: 1
+ maxItems: 74
+
+ interrupt-names:
+ description: |
+ The MHUv3 controller generates a number of events some of which are used
+ to generate interrupts; as a consequence it can expose a varying number of
+ optional PBX/MBX interrupts, representing the events generated during the
+ operation of the various transport protocols associated with different
+ extensions. All interrupts of the MHU are level-sensitive.
+ Some of these optional interrupts are defined per-channel, where the
+ number of channels effectively available is implementation defined and
+ run-time discoverable.
+ In the following names are enumerated using patterns, with per-channel
+ interrupts implicitly capped at the maximum channels allowed by the
+ specification for each extension type.
+ For the sake of simplicity maxItems is anyway capped to a most plausible
+ number, assuming way less channels would be implemented than actually
+ possible.
+
+ The only mandatory interrupts on the MHU are:
+ - combined
+ - mbx-fch-xfer-<N> but only if mbx-fcgrp-xfer-<N> is not implemented.
+
+ minItems: 1
+ maxItems: 74
+ items:
+ oneOf:
+ - const: combined
+ description: PBX/MBX Combined interrupt
+ - const: combined-ffch
+ description: PBX/MBX FIFO Combined interrupt
+ - pattern: '^ffch-low-tide-[0-9]+$'
+ description: PBX/MBX FIFO Channel <N> Low Tide interrupt
+ - pattern: '^ffch-high-tide-[0-9]+$'
+ description: PBX/MBX FIFO Channel <N> High Tide interrupt
+ - pattern: '^ffch-flush-[0-9]+$'
+ description: PBX/MBX FIFO Channel <N> Flush interrupt
+ - pattern: '^mbx-dbch-xfer-[0-9]+$'
+ description: MBX Doorbell Channel <N> Transfer interrupt
+ - pattern: '^mbx-fch-xfer-[0-9]+$'
+ description: MBX FastChannel <N> Transfer interrupt
+ - pattern: '^mbx-fchgrp-xfer-[0-9]+$'
+ description: MBX FastChannel <N> Group Transfer interrupt
+ - pattern: '^mbx-ffch-xfer-[0-9]+$'
+ description: MBX FIFO Channel <N> Transfer interrupt
+ - pattern: '^pbx-dbch-xfer-ack-[0-9]+$'
+ description: PBX Doorbell Channel <N> Transfer Ack interrupt
+ - pattern: '^pbx-ffch-xfer-ack-[0-9]+$'
+ description: PBX FIFO Channel <N> Transfer Ack interrupt
+
+ '#mbox-cells':
+ description: |
+ The first argument in the consumers 'mboxes' property represents the
+ extension type, the second is for the channel number while the third
+ depends on extension type.
+
+ Extension type for DBE is 0 and the third parameter represents the
+ doorbell flag number to use.
+ Extension type for FCE is 1, third parameter unused.
+ Extension type for FE is 2, third parameter unused.
+
+ mboxes = <&mhu 0 0 5>; // DBE, Doorbell Channel Window 0, doorbell flag 5.
+ mboxes = <&mhu 0 1 7>; // DBE, Doorbell Channel Window 1, doorbell flag 7.
+ mboxes = <&mhu 1 0 0>; // FCE, FastChannel Window 0.
+ mboxes = <&mhu 1 3 0>; // FCE, FastChannel Window 3.
+ mboxes = <&mhu 2 1 0>; // FE, FIFO Channel Window 1.
+ mboxes = <&mhu 2 7 0>; // FE, FIFO Channel Window 7.
+ const: 3
+
+ clocks:
+ maxItems: 1
+
+required:
+ - compatible
+ - reg
+ - interrupts
+ - interrupt-names
+ - '#mbox-cells'
+
+additionalProperties: false
+
+examples:
+ - |
+ soc {
+ #address-cells = <2>;
+ #size-cells = <2>;
+
+ mailbox@2aaa0000 {
+ compatible = "arm,mhuv3";
+ #mbox-cells = <3>;
+ reg = <0 0x2aaa0000 0 0x10000>;
+ clocks = <&clock 0>;
+ interrupt-names = "combined", "pbx-dbch-xfer-ack-1",
+ "ffch-high-tide-0";
+ interrupts = <0 36 4>, <0 37 4>;
+ };
+
+ mailbox@2ab00000 {
+ compatible = "arm,mhuv3";
+ #mbox-cells = <3>;
+ reg = <0 0x2aab0000 0 0x10000>;
+ clocks = <&clock 0>;
+ interrupt-names = "combined", "mbx-dbch-xfer-1", "ffch-low-tide-0";
+ interrupts = <0 35 4>, <0 38 4>, <0 39 4>;
+ };
+ };
--
2.34.1