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    Subject[PATCH V3] dt-bindings: mailbox: arm,mhuv2: Add bindings
    Date
    This patch adds device tree binding for ARM Message Handling Unit (MHU)
    controller version 2.

    Based on earlier work by Morten Borup Petersen.

    Co-developed-by: Tushar Khandelwal <tushar.khandelwal@arm.com>
    Signed-off-by: Tushar Khandelwal <tushar.khandelwal@arm.com>
    Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

    ---
    V2->V3:

    - compatible is changed to arm-mhuv2-tx/rx. Later version of MHUv2
    have an interrupt in the sender mode as well and we can't find if a
    mailbox is sender or receiver just based on an interrupt anymore. We
    needed a better way.

    - arm-mhuv2-mode is renamed to arm,mhuv2-protocols to fit the purpose
    better.

    - Minor formatting otherwise.

    - No longer an RFC.

    Morten: Please let me know if you want me to add your sign-off here from
    some other email id as you no longer work with ARM.
    ---
    .../bindings/mailbox/arm,mhuv2.yaml | 194 ++++++++++++++++++
    1 file changed, 194 insertions(+)
    create mode 100644 Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml

    diff --git a/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml
    new file mode 100644
    index 000000000000..a2b8ecd639c7
    --- /dev/null
    +++ b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml
    @@ -0,0 +1,194 @@
    +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
    +%YAML 1.2
    +---
    +$id: http://devicetree.org/schemas/mailbox/arm,mhuv2.yaml#
    +$schema: http://devicetree.org/meta-schemas/core.yaml#
    +
    +title: ARM MHUv2 Mailbox Controller
    +
    +maintainers:
    + - Tushar Khandelwal <tushar.khandelwal@arm.com>
    + - Viresh Kumar <viresh.kumar@linaro.org>
    +
    +description: |
    + The Arm Message Handling Unit (MHU) Version 2 is a mailbox controller that has
    + between 1 and 124 channel windows (each 32-bit wide) to provide unidirectional
    + communication with remote processor(s), where the number of channel windows
    + are implementation dependent.
    +
    + Given the unidirectional nature of the controller, an MHUv2 mailbox may only
    + be written to or read from. If a pair of MHU controllers is implemented
    + between two processing elements to provide bidirectional communication, these
    + must be specified as two separate mailboxes.
    +
    + If the interrupts property is present in device tree node, then its treated as
    + a "receiver" mailbox, otherwise a "sender".
    +
    + An MHU controller must be specified along with the supported transport
    + protocols. The transport protocols determine the method of data transmission
    + as well as the number of provided mailbox channels.
    +
    + Following are the possible transport protocols.
    +
    + - Doorbell: Each transfer is made up of single bit flag, using any one of the
    + bits in a channel window. A channel window can support up to 32 doorbells
    + and the entire window shall be used in doorbell protocol. Optionally, data
    + may be transmitted through a shared memory region, wherein the MHU is used
    + strictly as an interrupt generation mechanism but that is out of the scope
    + of these bindings.
    +
    + - Single-word: Each transfer is single word, using a single Channel window.
    +
    + - Multi-word: Each transfer is made of two or more words, using two or more
    + channel windows.
    +
    +# We need a select here so we don't match all nodes with 'arm,primecell'
    +select:
    + properties:
    + compatible:
    + contains:
    + enum:
    + - arm,mhuv2-tx
    + - arm,mhuv2-rx
    + required:
    + - compatible
    +
    +properties:
    + compatible:
    + oneOf:
    + - description: Sender mode
    + items:
    + - const: arm,mhuv2-tx
    + - const: arm,primecell
    +
    + - description: Receiver-mode
    + items:
    + - const: arm,mhuv2-rx
    + - const: arm,primecell
    +
    + reg:
    + maxItems: 1
    +
    + interrupts:
    + description: |
    + The MHUv2 controller always implements an interrupt in the "receiver"
    + mode, while the interrupt in the "sender" mode was not available in the
    + version MHUv2.0, but the later versions do have it.
    + maxItems: 1
    +
    + clocks:
    + maxItems: 1
    +
    + clock-names:
    + maxItems: 1
    +
    + arm,mhuv2-protocols:
    + $ref: /schemas/types.yaml#/definitions/uint32-matrix
    + description: |
    + The MHUv2 controller may contain up to 124 channel windows (each 32-bit
    + wide). The hardware and the DT bindings allows any combination of those to
    + be used for various transport protocols.
    +
    + This property allows a platform to describe how these channel windows are
    + used in various transport protocols. The entries in this property shall be
    + present as an array of tuples, where each tuple describes details about
    + one of the transport protocol being implemented over some channel
    + window(s).
    +
    + The first field of a tuple signifies the transfer protocol, 0 is reserved
    + for doorbell protocol, 1 is reserved for single-word protocol and 2 is
    + reserved for multi-word protocol. Using any other value in the first field
    + of a tuple makes it invalid.
    +
    + The second field of a tuple signifies the number of channel windows where
    + the protocol would be used. For doorbell protocol this field signifies the
    + number of 32-bit channel windows that implement the doorbell protocol. For
    + single-word protocol this field signifies the number of 32-bit channel
    + windows that implement separate single-word protocol mailbox channels. For
    + multi-word protocol this field signifies the number of channel windows
    + used for a multi-word protocol, it should be 2 or more.
    +
    + The total number of channel windows specified here shouldn't be more than
    + the ones implemented by the platform, though one can specify lesser number
    + of windows here than what the platform implements.
    +
    + mhu: mailbox@2b1f0000 {
    + ...
    +
    + arm,mhuv2-protocols = <0 2>, <1 3>, <2 5>, <2 7>;
    + }
    +
    + The above example defines the protocols of an ARM MHUv2 mailbox
    + controller, where a total of 17 channel windows are used. The first two
    + windows are used in doorbell protocol (64 doorbells), the next 3 windows
    + are (separately) used in single-word protocol, and the last two mailbox
    + channels are used in multi-word protocol of length 5 and 7 channel
    + windows.
    +
    + '#mbox-cells':
    + description: |
    + It contains two fields, the first field represents the channel number,
    + which may be used in doorbell, single-word, or multi-word protocol, and
    + the second field (only relevant in doorbell protocol, should be 0
    + otherwise) represents the doorbell number within the 32 bit wide channel
    + window.
    +
    + From the example given above for the arm,mhuv2-protocols, here is how a
    + client node can reference them.
    +
    + mboxes = <&mhu 0 5>; // Mailbox channel 0, doorbell 5.
    + mboxes = <&mhu 1 7>; // Mailbox channel 1, doorbell 7.
    + mboxes = <&mhu 2 0>; // Mailbox channel 2, single-word protocol.
    + mboxes = <&mhu 4 0>; // Mailbox channel 4, single-word protocol.
    + mboxes = <&mhu 6 0>; // Mailbox channel 6, multi-word protocol with 7 windows.
    +
    + const: 2
    +
    +required:
    + - compatible
    + - reg
    + - '#mbox-cells'
    + - arm,mhuv2-protocols
    +
    +additionalProperties: false
    +
    +examples:
    + # Multiple transport protocols implemented by the mailbox controllers
    + - |
    + soc {
    + #address-cells = <2>;
    + #size-cells = <2>;
    +
    + mhu_tx: mailbox-tx@2b1f0000 {
    + #mbox-cells = <2>;
    + compatible = "arm,mhuv2-tx", "arm,primecell";
    + reg = <0 0x2b1f0000 0 0x1000>;
    + clocks = <&clock 0>;
    + clock-names = "apb_pclk";
    + arm,mhuv2-protocols = <1 5>, <2 2>, <2 5>, <2 7>, <0 2>;
    + };
    +
    + mhu_rx: mailbox-rx@2b1f1000 {
    + #mbox-cells = <2>;
    + compatible = "arm,mhuv2-rx", "arm,primecell";
    + reg = <0 0x2b1f1000 0 0x1000>;
    + clocks = <&clock 0>;
    + clock-names = "apb_pclk";
    + arm,mhuv2-protocols = <1 5>, <2 7>, <0 2>;
    + };
    +
    + mhu_client: scb@2e000000 {
    + compatible = "fujitsu,mb86s70-scb-1.0";
    + reg = <0 0x2e000000 0 0x4000>;
    +
    + mboxes =
    + //single-word protocol channel 0, mhu-rx
    + <&mhu_rx 0 0>,
    + //single-word protocol channel 4, mhu-tx
    + <&mhu_tx 4 0>,
    + //multi-word protocol channel 6 with 5 windows, mhu-tx
    + <&mhu_tx 6 0>,
    + //doorbell protocol channel 9, doorbell 27, mhu-tx
    + <&mhu_tx 9 27>;
    + };
    + };
    --
    2.25.0.rc1.19.g042ed3e048af
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