linux-kernel - Re: [PATCH 4/5] firmware: Add coreboot device tree binding documentation

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Date:   Fri, 24 Mar 2017 12:33:34 -0700
From:   Julius Werner <jwerner@...omium.org>
To:     Julius Werner <jwerner@...omium.org>
Cc:     Brian Norris <briannorris@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Olof Johansson <olof@...om.net>,
        Stephen Warren <swarren@...dia.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 4/5] firmware: Add coreboot device tree binding documentation

...and again in plaintext, sorry about that.

On Fri, Mar 24, 2017 at 12:32 PM, Julius Werner <jwerner@...omium.org> wrote:
>> > Devicetree bindings should be in vendor,prefix format. This doesn't
>> > represent every aspect of coreboot, so it needs a more descriptive
>> > string.
>>
>> Any particular suggestion? I suppose this is Google's interpretation of
>> coreboot tables, so "google,coreboot"?
>
>
> No. This binding is for the coreboot project in general and has nothing to
> do with Google. coreboot is both the vendor and the product, so I think
> "coreboot" would look better than "coreboot,coreboot". And yes, it is
> supposed to represent every aspect of coreboot (right now the "coreboot
> tables" are already sort of a catch-all data structure used by coreboot to
> pass on any sort of info it wants later stages to know... and if we ever
> have any additional things we'd like to pass on, we'd probably want to add
> them to this binding as well).
>
>>
>> > > + - reg: Address and length of the following two memory regions, in
>> > > order:
>> > > +   1.) The coreboot table. This is a list of variable-sized
>> > > descriptors
>> > > +   that contain various compile- and run-time generated firmware
>> > > +   parameters. It is identified by the magic string "LBIO" in its
>> > > first
>> > > +   four bytes.
>> > > +   See coreboot's src/commonlib/include/commonlib/coreboot_tables.h
>> > > for
>> > > +   details.
>> >
>> > Given this is a memory region, it should be described under the
>> > reserved-memory node.
>>
>> We've painted this bikeshed before. I guess the result was either to use
>> /reserved-memory or /memreserve/. I believe we've been using
>> /memreserve/. I suppose we could document a method to use either, but
>> the main "agreement" was to use the /firmware/coreboot path instead of
>> /reserved-memory/coreboot.
>
>
> See the old thread Brian linked for some arguments for and against this. I
> think particularly because we want this node to represent every aspect of
> coreboot (which I think makes more sense than spreading stuff all over the
> place), treating it as reserved memory would not work well if we might later
> add other fields.
>
> Also, since we didn't get any more responses the last time we tried to
> upstream this and had schedules to keep, we had to go ahead with what we
> had. So right now there are already millions of devices shipped with this
> binding in firmware, and the only question we still have left to decide is
> whether Linux wants to support them upstream or not.