[PATCH 1/2] dt-bindings: mailbox: arm,mhuv3: Add bindings
Cristian Marussi
cristian.marussi at arm.com
Tue Mar 26 03:26:01 PDT 2024
On Mon, Mar 25, 2024 at 08:44:24AM -0500, Rob Herring wrote:
> On Mon, Mar 25, 2024 at 4:28 AM Cristian Marussi
> <cristian.marussi at arm.com> wrote:
> >
> > Add bindings for the ARM MHUv3 Mailbox controller.
> >
Hi Rob,
thanks for having a look.
> > Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>
> > ---
> > .../bindings/mailbox/arm,mhuv3.yaml | 239 ++++++++++++++++++
> > 1 file changed, 239 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..bfb8ec341d26
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mailbox/arm,mhuv3.yaml
> > @@ -0,0 +1,239 @@
> > +# 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 at arm.com>
> > + - Cristian Marussi <cristian.marussi at 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 implemented is between 1 and
> > + 128, numbered starting from 0 in ascending order.
> > + 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 FCH that an implementation of the MHU
> > + can support is between 1-1024, if the Fast Channel word-size is 32-bits, or
> > + between 1-512, when the Fast Channel word-size is 64-bits.
>
> Be consistent: FastChannel
>
I'll fix.
> > + FCHs are numbered from 0 in ascending order.
> > + Note that Fast Channel word-size is 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 Transfer to the Receiver without having to wait for a 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 FFCH an implementation of the MHU can
> > + support is between 1 and 64, numbered starting from the 0 in ascending
> > + order. The FIFO size is implementation defined and not configurable.
>
> Size is discoverable or opaque to s/w?
>
FIFOs depth is the same across all of the implemented FIFO channels (between 1 and
1024 bytes) AND it is actually discoverable at runtime...I forgot to mention that here,
I'll fix.
> > + 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: 38
> > +
> > + 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, for sake of simplicity, only a limited number of
> > + per-channel interrupt names are enumerated, out of all the possible
> > + channels allowed by the specification for each extension type.
> > +
> > + - "combined": PBX/MBX Combined interrupt
> > + - "combined-ffch": PBX/MBX FIFO Combined interrupt
> > + - "ffch-low-tide-<N>": PBX/MBX FIFO Channel <N> Low Tide interrupt
> > + - "ffch-high-tide-<N>": PBX/MBX FIFO Channel <N> High Tide interrupt
> > + - "ffch-flush-<N>": PBX/MBX FIFO Channel <N> Flush interrupt
> > + - "mbx-dbch-xfer-<N>": MBX Doorbell Channel <N> Transfer interrupt
> > + - "mbx-fch-xfer-<N>": MBX Fast Channel <N> Transfer interrupt
> > + - "mbx-fchgrp-xfer-<N>": MBX Fast Channel <N> Group Transfer interrupt
> > + - "mbx-ffch-xfer-<N>": MBX FIFO Channel <N> Transfer interrupt
> > + - "pbx-dbch-xfer-ack-<N>": PBX Doorbell Channel <N> Transfer Ack interrupt
> > + - "pbx-ffch-xfer-ack-<N>": PBX FIFO Channel <N> Transfer Ack interrupt
>
> It would be better to not define these strings twice. You can do
> something like this:
>
> items:
> oneOf:
> - const: combined
> description: ...
> - pattern: '^ffch-low-tide-[0-9]+$'
> description: ...
>
> And so on.
>
Thanks, I'll give it a go.
> > +
> > + 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: 38
>
> Perhaps a comment on where 38 comes from. AIUI, this is a "should be
> enough for now" value.
>
Yes, I'll add and explanation to justify this.
> > + items:
> > + enum:
> > + - combined
> > + - combined-ffch
> > + - ffch-low-tide-0
> > + - ffch-low-tide-1
> > + - ffch-low-tide-2
> > + - ffch-low-tide-3
> > + - ffch-high-tide-0
> > + - ffch-high-tide-1
> > + - ffch-high-tide-2
> > + - ffch-high-tide-3
> > + - ffch-flush-0
> > + - ffch-flush-1
> > + - ffch-flush-2
> > + - ffch-flush-3
> > + - mbx-dbch-xfer-0
> > + - mbx-dbch-xfer-1
> > + - mbx-dbch-xfer-2
> > + - mbx-dbch-xfer-3
> > + - mbx-fch-xfer-0
> > + - mbx-fch-xfer-1
> > + - mbx-fch-xfer-2
> > + - mbx-fch-xfer-3
> > + - mbx-fchgrp-xfer-0
> > + - mbx-fchgrp-xfer-1
> > + - mbx-fchgrp-xfer-2
> > + - mbx-fchgrp-xfer-3
> > + - mbx-ffch-xfer-0
> > + - mbx-ffch-xfer-1
> > + - mbx-ffch-xfer-2
> > + - mbx-ffch-xfer-3
> > + - pbx-dbch-xfer-ack-0
> > + - pbx-dbch-xfer-ack-1
> > + - pbx-dbch-xfer-ack-2
> > + - pbx-dbch-xfer-ack-3
> > + - pbx-ffch-xfer-ack-0
> > + - pbx-ffch-xfer-ack-1
> > + - pbx-ffch-xfer-ack-2
> > + - pbx-ffch-xfer-ack-3
> > +
> > + '#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, Fast Channel Window 0.
> > + mboxes = <&mhu 1 3 0>; // FCE, Fast Channel 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>;
> > +
> > + mhu_tx: mailbox at 2aaa0000 {
>
> Drop unused labels.
>
Ok.
Thanks,
Cristian
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