linux-kernel - Re: [PATCH v1 3/3] Revert "Revert "driver core: Set fw

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Date:   Tue, 27 Apr 2021 17:39:13 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Cristian Marussi <cristian.marussi@....com>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Al Cooper <alcooperx@...il.com>,
        Michael Walle <michael@...le.cc>,
        Jon Hunter <jonathanh@...dia.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/3] Revert "Revert "driver core: Set fw_devlink=on by
 default""

On Tue, Apr 27, 2021 at 09:24:55AM -0700, Florian Fainelli wrote:

[...]

> 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 assume the bootloader checks the presence of SMC support and modifies
the DT node accordingly. Can't it remove the mbox properties as it make
no sense with SMC compatible ? However ...

> >
> > 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?

I *think* we could do that in the SCMI drivers, but:
1. I am not sure if that helps fw_devlinks if they are deriving the info
   purely based on DT
2. I am also afraid that someone might come up with exactly opposite
   requirement that let us prefer mailbox over SMC as they would use
   SMC only if h/w lacks proper mailbox support. I fear that we will get
   into rabbit hole trying to do something like that.

--
Regards,
Sudeep