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

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Message-ID: <20201105190534.jnbbnquihkryxnup@bogus>
Date:   Thu, 5 Nov 2020 19:05:34 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     Rob Herring <robh@...nel.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Sudeep Holla <sudeep.holla@....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 Thu, Nov 05, 2020 at 01:57:07PM -0500, Jim Quinlan wrote:
> On Thu, Nov 5, 2020 at 1:27 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Thu, Nov 05, 2020 at 10:28:25AM -0500, Jim Quinlan wrote:
> > > On Thu, Nov 5, 2020 at 10:13 AM Rob Herring <robh@...nel.org> wrote:
> > > >
> > > > 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?
> > >
> > > Correct.  Although you can see that it uses both interrupts and SMC
> > > calls to get the job done.
> > >
> >
> > I was against having 2 separate solutions and would have raised my concern
> > again. As I mentioned earlier, either extend what we have or move the
> > existing SMC solution into this mailbox driver. Having 2 different solution
> > for this just because you have extra interrupt to deal with is definite
> > NACK from me as I had previously mentioned.
> >
> > > > So why not either
> > > > allow SCMI to have an interrupt directly
> > > Not sure here -- perhaps the SCMI folks have an answer?
> > >
> >
> > I did ask why can't you extend the existing SCMI/SMC binding to add this
> > as optional feature ?
> Hi Sudeep,
> 
> Looking at the email you said, "In that case any reason why you can't
> reuse the existing smc transport for SCMI." ,  and I replied with the
> reason.  I did not interpret your statement  above as what you are
> clearly saying now: "either extend what we have or move the existing
> SMC solution into this mailbox driver. "
>

No, you are right. I didn't mention that explicitly. I wanted to, but
thought I will wait until this driver got traction to ask you to merge
them. Sorry for that. Anyways I am against having existing solution and
a mailbox for SMC, they need to be merged at any cost. Where the final
solution will be doesn't matter much to me, I am fine either way.

--
Regards,
Sudeep