linux-kernel - Re: [PATCH] acpi, spcr: Make SPCR available to x86

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Message-ID: <20180212145652.GM25181@hirez.programming.kicks-ass.net>
Date:   Mon, 12 Feb 2018 15:56:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, linux-serial@...r.kernel.org,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Lv Zheng <lv.zheng@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Timur Tabi <timur@...eaurora.org>, graeme.gregory@...aro.org,
        mark.salter@...hat.com
Subject: Re: [PATCH] acpi, spcr: Make SPCR available to x86

On Mon, Feb 12, 2018 at 08:47:57AM -0500, Prarit Bhargava wrote:
> 
> 
> On 02/12/2018 08:34 AM, Peter Zijlstra wrote:
> > On Thu, Jan 18, 2018 at 10:09:51AM -0500, Prarit Bhargava wrote:
> >>  config ACPI_SPCR_TABLE
> >> +	bool "ACPI Serial Port Console Redirection Support"
> >> +	default y if X86
> >> +	help
> >> +	  Enable support for Serial Port Console Redirection (SPCR) Table.
> >> +	  This table provides information about the configuration of the
> >> +	  earlycon console.
> > 
> > I just got asked this by oldconfig, which left me rather puzzled, WTF
> > does this do?
> 
> Odd -- I thought I had taken care of that :(  My apologies Peter.
> 
> ACPI SPCR is used by a vendor to define the serial console for a system.  If
> SPCR exists a user can add kernel parameter "earlycon" (no extra kernel
> parameters) and the console will work out-of-the-box.
> 
> The serial console configuration varies from vendor to vendor.  This takes the
> guess-work out of defining a serial console.

But when I specify "earlyprintk=serial,ttyS0,115200" this SPCR crud will
not interfere?