linux-kernel - Re: [PATCH 1/3] serial: 8250_early: Add earlycon support for AMD Carrizo / Stoneyridge

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Message-ID: <CAE2855tmMwbOWDOs-iJS7i35=Y7gt0xun4ApfhZyY9Kr5N3NJA@mail.gmail.com>
Date:   Sun, 1 Apr 2018 11:54:41 -0700
From:   Aaron Durbin <adurbin@...omium.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Aaron Durbin <adurbin@...omium.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        Doug Anderson <dianders@...omium.org>,
        Matt Redfearn <matt.redfearn@...s.com>,
        Jeffy <jeffy.chen@...k-chips.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] serial: 8250_early: Add earlycon support for AMD
 Carrizo / Stoneyridge

On Thu, Mar 29, 2018 at 6:34 AM, Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
> On Mon, 26 Mar 2018 20:56:45 -0600
> Aaron Durbin <adurbin@...omium.org> wrote:
>
>> On Mon, Mar 26, 2018 at 12:24 PM, Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
>> >> Sadly, this situation
>> >> is not unique to this hardware. There is hardware all over that does
>> >> not meet the current assumptions being made in the early uart drivers
>> >> within the kernel.
>> >
>> > Is there any fundamental reason you can't just embed dt entries in the
>> > ACPI table to describe the other features you need. I appreciate it
>> > doesn't solve the generic PC case but it ought to help for anything where
>> > the firmware cares about Linux ?
>>
>> What's the method for doing that? Using _DSD methods? Or have a
>> pointer to examples? Sorry, I haven't spelunked into the current state
>> of bridging ACPI and devicetree in a while.
>
> ACPI 5.1 adds an _DSD method UUID for device properties.
>
> The kernel device_property_* interface will pick them up just as if they
> came from DT tables etc.

But we don't have the full ACPI interpreter up in the early part of
the kernel. All these 'early' devices have their own setup/config
which is the source of the issue. Or maybe I am wrong about the full
interpreter and the early drivers are just not taking advantage of the
ACPI device binding?

-Aaron