linux-kernel - Re: [PATCH 1/3] firmware: of: populate /firmware/ node during init

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Date:   Fri, 11 Aug 2017 10:05:43 -0500
From:   Rob Herring <robh@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh@...nel.org>,
        Andy Gross <andy.gross@...aro.org>,
        Jens Wiklander <jens.wiklander@...aro.org>
Subject: Re: [PATCH 1/3] firmware: of: populate /firmware/ node during init

On Fri, Aug 11, 2017 at 9:37 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Aug 11, 2017 at 3:30 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>> Since "/firmware" does not have its own "compatible" property as it's
>> just collection of nodes representing firmware interface, it's sub-nodes
>> are not populated during system initialization.
>>
>> Currently different firmware drivers search the /firmware/ node and
>> populate the sub-node devices selectively. Instead we can populate
>> the /firmware/ node during init to avoid more drivers continuing to
>> populate the devices selectively.
>>
>> This patch adds initcall to achieve the same.
>
> Hmm, I'm a bit skeptical whether representing anything under /firmware
> as a platform device is a good idea. Having a more structured way to
> probe those seems like a good idea, but maybe a different subsystem
> would be more appropriate.
>
> I do realize that a 'platform_device' has become a rather generic abstraction
> for almost anything, but at some point we might want to draw the line
> of what is a platform_device.

I guess the question how are they different? Most of what's under
drivers/firmware/ are platform drivers. I think they are mostly either
smc calls or mailbox interfaces. Would there be any advantage to
creating an smc bus or mailbox bus?

It's easier to convert from a platform driver to some new bus_type
than convert from a non-driver if we decide to do that later.

The other approach would be to do a whitelist of compatibles. That's
what's being done for /reserved-memory (currently there's one
(ramoops) and a 2nd is being added).

Rob