Re: [PATCH V2] dt-bindings: mailbox: add doorbell support to ARM MHU

[Rob Herring <robh+dt@kernel.org>]

On Wed, Sep 9, 2020 at 12:19 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> From: Sudeep Holla <sudeep.holla@arm.com>
>
> The ARM MHU's reference manual states following:
>
> "The MHU drives the signal using a 32-bit register, with all 32 bits
> logically ORed together. The MHU provides a set of registers to enable
> software to set, clear, and check the status of each of the bits of this
> register independently.  The use of 32 bits for each interrupt line
> enables software to provide more information about the source of the
> interrupt. For example, each bit of the register can be associated with
> a type of event that can contribute to raising the interrupt."
>
> This patch thus extends the MHU controller's DT binding to add support
> for doorbell mode.
>
> Though the same MHU hardware controller is used in the two modes, A new
> compatible string is added here to represent the combination of the MHU
> hardware and the firmware sitting on the other side (which expects each
> bit to represent a different signal now).
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Co-developed-by: Viresh Kumar <viresh.kumar@linaro.org>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> V2:
> - New compatible string and minor reformatting.

Fine with me despite whatever I may have said in the past. Whatever
puts this to rest finally.

> - Not sending as RFC anymore.
>
>  .../devicetree/bindings/mailbox/arm-mhu.txt   | 44 +++++++++++++++++--
>  1 file changed, 41 insertions(+), 3 deletions(-)

I'd really like this converted to schema first given it's more than a
minor change, but I don't want to hold things up. (Though, where's the
new driver?)

> diff --git a/Documentation/devicetree/bindings/mailbox/arm-mhu.txt b/Documentation/devicetree/bindings/mailbox/arm-mhu.txt
> index 4971f03f0b33..1adc441a2c63 100644
> --- a/Documentation/devicetree/bindings/mailbox/arm-mhu.txt
> +++ b/Documentation/devicetree/bindings/mailbox/arm-mhu.txt
> @@ -10,21 +10,41 @@ STAT register and the remote clears it after having read the data.
>  The last channel is specified to be a 'Secure' resource, hence can't be
>  used by Linux running NS.
>
> +Doorbell mode: The MHU drives the interrupt signal using a 32-bit
> +register, with all 32-bits logically ORed together. It provides a set of
> +registers to enable software to set, clear and check the status of each
> +of the bits of this register independently. The use of 32 bits per
> +interrupt line enables software to provide more information about the
> +source of the interrupt. For example, each bit of the register can be
> +associated with a type of event that can contribute to raising the
> +interrupt. Each of the 32-bits can be used as "doorbell" to alert the
> +remote processor.
> +
>  Mailbox Device Node:
>  ====================
>
>  Required properties:
>  --------------------
> -- compatible:          Shall be "arm,mhu" & "arm,primecell"
> +- compatible:          Shall be "arm,mhu" (in data transfer mode) or
> +                       "arm,mhu-doorbell" (in doorbell mode) and
> +                       "arm,primecell".
>  - reg:                 Contains the mailbox register address range (base
>                         address and length)
> -- #mbox-cells          Shall be 1 - the index of the channel needed.
> +- #mbox-cells          Shall be 1 - the index of the channel needed,
> +                       when used in data transfer mode.
> +                       Shall be 2 - the index of the channel needed, and
> +                       the index of the doorbell bit within the
> +                       channel, when used in doorbell mode.
>  - interrupts:          Contains the interrupt information corresponding to
> -                       each of the 3 links of MHU.
> +                       each of the 3 physical channels of MHU namely low
> +                       priority non-secure, high priority non-secure and
> +                       secure channels.
>
>  Example:
>  --------
>
> +1. In data transfer mode
> +
>         mhu: mailbox@2b1f0000 {
>                 #mbox-cells = <1>;
>                 compatible = "arm,mhu", "arm,primecell";
> @@ -41,3 +61,21 @@ used by Linux running NS.
>                 reg = <0 0x2e000000 0x4000>;
>                 mboxes = <&mhu 1>; /* HP-NonSecure */
>         };
> +
> +2. In doorbell mode
> +
> +       mhu: mailbox@2b1f0000 {
> +               #mbox-cells = <2>;
> +               compatible = "arm,mhu-doorbell", "arm,primecell";
> +               reg = <0 0x2b1f0000 0x1000>;
> +               interrupts = <0 36 4>, /* LP-NonSecure */
> +                            <0 35 4>; /* HP-NonSecure */

The binding says there are 3 interrupts.

> +               clocks = <&clock 0 2 1>;
> +               clock-names = "apb_pclk";
> +       };
> +
> +       mhu_client: scb@2e000000 {
> +               compatible = "arm,scpi";
> +               reg = <0 0x2e000000 0x200>;
> +               mboxes = <&mhu 1 4>; /* HP-NonSecure 5th doorbell bit */
> +       };
> --
> 2.25.0.rc1.19.g042ed3e048af
>