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From:   Saravana Kannan <saravanak@google.com>
Date:   Tue, 27 Apr 2021 09:28:16 -0700
Message-ID: <CAGETcx9rcrdzt0QqSNDEsMN4Gfay8kryNjTktAuyBEQX74S9Vg@mail.gmail.com>
Subject: Re: [PATCH v1 3/3] Revert "Revert "driver core: Set fw_devlink=on by default""
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     Sudeep Holla <sudeep.holla@arm.com>,
        Cristian Marussi <cristian.marussi@arm.com>,
        Jim Quinlan <james.quinlan@broadcom.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Al Cooper <alcooperx@gmail.com>,
        Michael Walle <michael@walle.cc>,
        Jon Hunter <jonathanh@nvidia.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Android Kernel Team <kernel-team@android.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Apr 27, 2021 at 9:25 AM Florian Fainelli <f.fainelli@gmail.com> wrote:
>
>
>
> On 4/27/2021 8:10 AM, Sudeep Holla wrote:
> > On Tue, Apr 27, 2021 at 03:11:16PM +0100, Cristian Marussi wrote:
> >> On Tue, Apr 27, 2021 at 09:33:31AM -0400, Jim Quinlan wrote:
> > [...]
> >>>>
> >>> I believe that the brcmstb-mbox node is in our DT for backwards
> >>> compatibility with our older Linux only.   Note that  we use the compatible
> >>> string '"arm,scmi-smc", "arm,scmi"'; the former chooses SMC transport and
> >>> ignores custom  mailboxes such as brcmstb-mbox.
> >>>
> >>
> >> Right..so it is even more wrong that it is waiting for the mailboxes...but
> >> looking at the DT:
> >>
> >> brcm_scmi_mailbox@0 {
> >>                 #mbox-cells = <0x01>;
> >>                 compatible = "brcm,brcmstb-mbox";
> >>                 status = "disabled";
> >>                 linux,phandle = <0x04>;
> >>                 phandle = <0x04>;
> >>         };
> >>
> >> brcm_scmi@0 {
> >>                 compatible = "arm,scmi-smc\0arm,scmi";
> >>                 mboxes = <0x04 0x00 0x04 0x01>;
> >>                 mbox-names = "tx\0rx";
> >>                 shmem = <0x05>;
> >>                 status = "disabled";
> >>                 arm,smc-id = <0x83000400>;
> >>                 interrupt-names = "a2p";
> >>                 #address-cells = <0x01>;
> >>                 #size-cells = <0x00>;
> >>
> >> it seems to me that even though you declare an SMC based transport (and in fact
> >> you define the smc-id too) you also still define mboxes (as a fallback I suppose)
> >> referring to the brcm_scmi_mailbox phandle, and while this is ignored by the SCMI
> >> driver (because you have selected a compatible SMC transport) I imagine this dep
> >> is picked up by fw_devlink which in fact says:
> >>
> >>> [    0.300086] platform brcm_scmi@0: Linked as a consumer to brcm_scmi_mailbox@0
> >>
> >> and stalls waiting for it. (but I'm not really familiar on how fw_devlink
> >> internals works really...so I maybe off in these regards)
> >>
> >
> > I was about to mention/ask the same when I saw Jim's reply. I see you have
> > already asked that. Couple of my opinions based on my very limited knowledge
> > on fw_devlink and how it works.
> >
> > 1. Since we have different compatible for SMC and mailbox, I am not sure
> >    if it correct to leave mailbox information in scmi node. Once we have
> >    proper yaml scheme, we must flag that error IMO.
>
> This is a self inflicted problem that we have in that the bootloader
> provides a Device Tree to the kernel which is massaged in different ways
> and intends to stay backwards compatible as much as possible. And indeed
> after removing the 'mboxes' property gets us going with fw_devlink=on.

I'm sure you'll see my other email and reply to it, so I'll not
respond to this part.

>
> >
> > 2. IIUC, the fw_devlink might use information from DT to establish the
> >    dependency and having mailbox information in this context may be
> >    considered wrong as there is no dependency if it is using SMC.
>
> Right, unfortunately, short of having some special casing for SCMI and
> checking that if we have both an "arm,smc-id" and "mboxes" phandle we
> should prefer the former, there is not probably much that can be done
> here. Do we want to do that?

Definite no for special casing per device nodes in fw_devlink code :)

-Saravana