linux-kernel - Re: [PATCH v4 1/2] dt-bindings: Add bindings for BrcmSTB SCMI mailbox driver

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Date:   Thu, 5 Nov 2020 09:13:00 -0600
From:   Rob Herring <robh@...nel.org>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] dt-bindings: Add bindings for BrcmSTB SCMI mailbox driver

On Wed, Nov 4, 2020 at 4:04 PM Jim Quinlan <james.quinlan@...adcom.com> wrote:
>
> On Wed, Nov 4, 2020 at 4:50 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Oct 29, 2020 at 03:59:06PM -0400, Jim Quinlan wrote:
> > > Bindings are added.  Only one interrupt is needed because
> > > we do not yet employ the SCMI p2a channel.
> >
> > I still don't understand what this is. To repeat from v1: I thought SCMI
> > was a mailbox consumer, not provider?
>
> Hi Rob,
>
> I'm not sure where I am implying that SCMI is a mailbox provider?
> Should I not mention "SCMI" in the subject line?
>
> This is just a mailbox driver, "consumed" by SCMI.    Our SCMI DT node
> looks like this:
>
> brcm_scmi_mailbox: brcm_scmi_mailbox@0 {
>         #mbox-cells = <1>;
>         compatible = "brcm,brcmstb-mbox";
> };
>
> brcm_scmi@0 {
>         compatible = "arm,scmi";
>         mboxes = <&brcm_scmi_mailbox 0>;;
>         mbox-names = "tx";
>         shmem = <&NWMBOX>;
>         /* ... */
> };

Okay, that makes more sense. Though it seems like this is just adding
a pointless level of indirection to turn an interrupt into a mailbox.
There's nothing more to 'the mailbox' is there? So why not either
allow SCMI to have an interrupt directly or have a generic irq mailbox
driver?

Rob