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

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Message-ID: <CAHp75VehhNv6pPrRiM9jBAK9FsqZ2Defo8HKhutwn+GPnCFp3w@mail.gmail.com>
Date:   Wed, 14 Mar 2018 18:38:38 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Daniel Kurtz <djkurtz@...omium.org>
Cc:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
        Aaron Durbin <adurbin@...omium.org>,
        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 Wed, Mar 14, 2018 at 6:29 PM, Daniel Kurtz <djkurtz@...omium.org> wrote:
> On Wed, Mar 14, 2018 at 4:54 AM Ricardo Ribalda Delgado <
> ricardo.ribalda@...il.com> wrote:
>> On Wed, Mar 14, 2018 at 1:36 AM, Daniel Kurtz <djkurtz@...omium.org>
> wrote:

> In fact, the recommended way is to have firmware specify an ACPI SPCR table
> with OEMID="AMDCZ " (see https://patchwork.kernel.org/patch/10281307/) to
> configure proper access and address.

Hmm... I was thinking it's already there. And thus, this is just a
quirk for *existing* firmware that doesn't correctly configured
hardware.
(Yes, I'm aware about one nuance in SPCR specification I'm trying to
address via official ways)

>  With an SPCR table in place,  the
> kernel command line just becomes "earlycon", with no parameters.

SPCR *provides* an address of UART (required by specification).

-- 
With Best Regards,
Andy Shevchenko