linux-kernel - Re: [PATCH 2/2] acpi, x86: Use SPCR table for earlycon on x86

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Date:   Thu, 7 Dec 2017 14:03:20 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     Timur Tabi <timur@...eaurora.org>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-pm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        linux-doc@...r.kernel.org, Will Deacon <will.deacon@....com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Lv Zheng <lv.zheng@...el.com>, linux-serial@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>
Subject: Re: [PATCH 2/2] acpi, x86: Use SPCR table for earlycon on x86



On 12/07/2017 01:46 PM, Timur Tabi wrote:
> On Thu, Dec 7, 2017 at 11:29 AM, Prarit Bhargava <prarit@...hat.com> wrote:
>> -int __init acpi_parse_spcr(bool earlycon)
>> +int __init acpi_parse_spcr(bool earlycon, bool enable_console)
>>  {
>>         static char opts[ACPI_SPCR_OPTS_SIZE];
>>         static char uart[ACPI_SPCR_BUF_SIZE];
>> @@ -113,7 +113,8 @@ int __init acpi_parse_spcr(bool earlycon)
>>         if (earlycon)
>>                 setup_earlycon(opts);
>>
>> -       err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
>> +       if (enable_console)
>> +               err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
> 
> So if earlycon==true but enable_console==false, then you parse SPCR
> and use it for the early console, but not the primary console?  I'm
> not sure what that gives you.
> 

On arm64 the original SPCR code provides both early and primary consoles (as
you've pointed out).  IOW, if SPRC exists on arm64 a console will be
initialized.  That is still the case after my change.

The expected behaviour on x86 is that unless someone specifies 'earlycon' or
'console=' that no console should be initialized.  There are users (some IOT
boxes, etc.) that do NOT want a console.

The above code keeps the existing x86 behaviour.

P.