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

[Jassi Brar <jassisinghbrar@gmail.com>]

On Fri, Aug 2, 2019 at 5:41 AM Morten Borup Petersen <morten_bp@live.dk> wrote:
>
>
>
> On 7/31/19 9:31 AM, Jassi Brar wrote:
> > On Sun, Jul 28, 2019 at 4:28 PM Morten Borup Petersen <morten_bp@live.dk> wrote:
> >>
> >>
> >>
> >> On 7/25/19 7:49 AM, Jassi Brar wrote:
> >>> On Sun, Jul 21, 2019 at 4:58 PM Jassi Brar <jassisinghbrar@gmail.com> 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?
> >>>>
> >>> Thinking about it, IMO, the mbox-cell should carry a 128 (4x32) bit
> >>> mask specifying the set of windows (corresponding to the bits set in
> >>> the mask) associated with the channel.
> >>> And the controller driver should see any channel as associated with
> >>> variable number of windows 'N', where N is [0,124]
> >>>
> >>> mhu_client1: proto1@2e000000 {
> >>>        .....
> >>>        mboxes = <&mbox 0x0 0x0 0x0 0x1>
> >>> }
> >>>
> >>> mhu_client2: proto2@2f000000 {
> >>>        .....
> >>>        mboxes = <&mbox 0x0 0x0 0x0 0x6>
> >>> }
> >>>
> >>> Cheers!
> >>>
> >>
> >> As mentioned in the response to your initial comment, the driver does
> >> not currently support mixing protocols.
> >>
> > Thanks for acknowledging that limitation. But lets also address it.
> >
>
> We are hesitant to dedicate time to developing mixing protocols given
> that we don't have any current usecase nor any current platform which
> would support this.
>
Can you please share the client code against which you tested this driver?
>From my past experience, I realise it is much more efficient to tidyup
the code myself, than endlessly trying to explain the benefits.

Thanks