Re: [PATCH 1/4] mailbox: arm_mhuv2: add device tree binding documentation

[Tushar K <tushar.2nov@gmail.com>]

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Please ignore the disclaimers in the previous replies. This is a problem
with the server which I am looking into.

On Wed, 7 Aug 2019 at 12:17, Tushar Khandelwal <Tushar.Khandelwal@arm.com>
wrote:

>
>
> On 02/08/2019, 11:59, "Sudeep Holla" <sudeep.holla@arm.com> wrote:
>
>     On Sun, Jul 21, 2019 at 04:58:04PM -0500, Jassi Brar wrote:
>     > On Wed, Jul 17, 2019 at 2:26 PM Tushar Khandelwal
>     > <tushar.khandelwal@arm.com> wrote:
>     >
>     > > diff --git
> a/Documentation/devicetree/bindings/mailbox/arm,mhuv2.txt
> b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.txt
>     > > new file mode 100644
>     > > index 000000000000..3a05593414bc
>     > > --- /dev/null
>     > > +++ b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.txt
>     > > @@ -0,0 +1,108 @@
>     > > +Arm MHUv2 Mailbox Driver
>     > > +========================
>     > > +
>     > > +The Arm Message-Handling-Unit (MHU) Version 2 is a mailbox
> controller that has
>     > > +between 1 and 124 channel windows to provide unidirectional
> communication with
>     > > +remote processor(s).
>     > > +
>     > > +Given the unidirectional nature of the device, an MHUv2 mailbox
> may only be
>     > > +written to or read from. If a pair of MHU devices is implemented
> between two
>     > > +processing elements to provide bidirectional communication, these
> must be
>     > > +specified as two separate mailboxes.
>     > > +
>     > > +A device tree node for an Arm MHUv2 device must specify either a
> receiver frame
>     > > +or a sender frame, indicating which end of the unidirectional MHU
> device which
>     > > +the device node entry describes.
>     > > +
>     > > +An MHU device must be specified with a transport protocol. The
> transport
>     > > +protocol of an MHU device determines the method of data
> transmission as well as
>     > > +the number of provided mailboxes.
>     > > +Following are the possible transport protocol types:
>     > > +- Single-word: An MHU device implements as many mailboxes as it
>     > > +               provides channel windows. Data is transmitted
> through
>     > > +               the MHU registers.
>     > > +- Multi-word:  An MHU device implements a single mailbox. All
> channel windows
>     > > +               will be used during transmission. Data is
> transmitted through
>     > > +               the MHU registers.
>     > > +- Doorbell:    An MHU device implements as many mailboxes as
> there are flag
>     > > +               bits available in its channel windows. Optionally,
> data may
>     > > +               be transmitted through a shared memory region,
> wherein the MHU
>     > > +               is used strictly as an interrupt generation
> mechanism.
>     > > +
>     > > +Mailbox Device Node:
>     > > +====================
>     > > +
>     > > +Required properties:
>     > > +--------------------
>     > > +- compatible:  Shall be "arm,mhuv2" & "arm,primecell"
>     > > +- reg:         Contains the mailbox register address range (base
>     > > +               address and length)
>     > > +- #mbox-cells  Shall be 1 - the index of the channel needed.
>     > > +- mhu-frame    Frame type of the device.
>     > > +               Shall be either "sender" or "receiver"
>     > > +- mhu-protocol Transport protocol of the device. Shall be one of
> the
>     > > +               following: "single-word", "multi-word", "doorbell"
>     > > +
>     > > +Required properties (receiver frame):
>     > > +-------------------------------------
>     > > +- interrupts:  Contains the interrupt information corresponding
> to the
>     > > +               combined interrupt of the receiver frame
>     > > +
>     > > +Example:
>     > > +--------
>     > > +
>     > > +       mbox_mw_tx: mhu@10000000 {
>     > > +               compatible = "arm,mhuv2","arm,primecell";
>     > > +               reg = <0x10000000 0x1000>;
>     > > +               clocks = <&refclk100mhz>;
>     > > +               clock-names = "apb_pclk";
>     > > +               #mbox-cells = <1>;
>     > > +               mhu-protocol = "multi-word";
>     > > +               mhu-frame = "sender";
>     > > +       };
>     > > +
>     > > +       mbox_sw_tx: mhu@10000000 {
>     > > +               compatible = "arm,mhuv2","arm,primecell";
>     > > +               reg = <0x11000000 0x1000>;
>     > > +               clocks = <&refclk100mhz>;
>     > > +               clock-names = "apb_pclk";
>     > > +               #mbox-cells = <1>;
>     > > +               mhu-protocol = "single-word";
>     > > +               mhu-frame = "sender";
>     > > +       };
>     > > +
>     > > +       mbox_db_rx: mhu@10000000 {
>     > > +               compatible = "arm,mhuv2","arm,primecell";
>     > > +               reg = <0x12000000 0x1000>;
>     > > +               clocks = <&refclk100mhz>;
>     > > +               clock-names = "apb_pclk";
>     > > +               #mbox-cells = <1>;
>     > > +               interrupts = <0 45 4>;
>     > > +               interrupt-names = "mhu_rx";
>     > > +               mhu-protocol = "doorbell";
>     > > +               mhu-frame = "receiver";
>     > > +       };
>     > > +
>     > > +       mhu_client: scb@2e000000 {
>     > > +       compatible = "fujitsu,mb86s70-scb-1.0";
>     > > +       reg = <0 0x2e000000 0x4000>;
>     > > +       mboxes =
>     > > +               // For multi-word frames, client may only
> instantiate a single
>     > > +               // mailbox for a mailbox controller
>     > > +               <&mbox_mw_tx 0>,
>     > > +
>     > > +               // For single-word frames, client may instantiate
> as many
>     > > +               // mailboxes as there are channel windows in the
> MHU
>     > > +                <&mbox_sw_tx 0>,
>     > > +                <&mbox_sw_tx 1>,
>     > > +                <&mbox_sw_tx 2>,
>     > > +                <&mbox_sw_tx 3>,
>     > > +
>     > > +               // For doorbell frames, client may instantiate as
> many mailboxes
>     > > +               // as there are bits available in the combined
> number of channel
>     > > +               // windows ((channel windows * 32) mailboxes)
>     > > +                <mbox_db_rx 0>,
>     > > +                <mbox_db_rx 1>,
>     > > +                ...
>     > > +                <mbox_db_rx 17>;
>     > > +       };
>     >
>     > If the mhuv2 instance implements, say, 3 channel windows between
>     > sender (linux) and receiver (firmware), and Linux runs two protocols
>     > each requiring 1 and 2-word sized messages respectively. The hardware
>     > supports that by assigning windows [0] and [1,2] to each protocol.
>     > However, I don't think the driver can support that. Or does it?
>     >
>
>     FWIW, the IP is designed to cover wide range of usecase from IoT to
> servers
>     with variable window length. I don't see the need to complicate the
> driver
>     supporting mix-n-match at the cost of latency. Each platform choose one
>     transport protocol for all it's use.
>
> The driver design is to address the most probable scenarios and not all.
> Single-word : Client gets one 32-bit window
> Doorbell : Client gets 32 data pointers (arm_message)
> Multi-word: Client gets all channels available in the platform.
>
> --Tushar
>     --
>     Regards,
>     Sudeep
>
>
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