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Message-ID: <1516100104.7000.1001.camel@linux.intel.com>
Subject: Re: [PATCH v1 4/6] x86/boot: Assume MMIO if serial base address
 supplied via earlyprintk
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Date: Tue, 16 Jan 2018 12:55:04 +0200
In-Reply-To: <20180116031342.bxczth3ylbzdvk2r@gmail.com>
References: <20180114143254.15429-1-andriy.shevchenko@linux.intel.com>
         <20180114143254.15429-4-andriy.shevchenko@linux.intel.com>
         <20180116031342.bxczth3ylbzdvk2r@gmail.com>
Organization: Intel Finland Oy
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On Tue, 2018-01-16 at 04:13 +0100, Ingo Molnar wrote:
> * Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> 
> > If user supplied serial base address via kernel command line and
> > value
> > is higher than IO space limit (64k boundary), assume for now that
> > MMIO
> > byte access is required.
> > 
> > Later we might expand or modify this if needed.
> 
> Is this a standard pattern for serial code configuration values?

I didn't get what you meant under "standard" here.

IO space limit comes from generic io.h header and AFAIU is a hardware
limitation (outN (%dx), ...; inX (%dx); dx is 16 bit register).

Using mmio8 out of the IO space is dictated by the (modern) x86
platforms with non-standard (okay, high speed) UART location in address
space.

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy