From owner-freebsd-hackers@freebsd.org  Wed Sep 16 03:59:15 2015
Return-Path: <owner-freebsd-hackers@freebsd.org>
Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id A5E8A9CD7F4;
 Wed, 16 Sep 2015 03:59:15 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1])
 (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 3973E187B;
 Wed, 16 Sep 2015 03:59:15 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from tom.home (kostik@localhost [127.0.0.1])
 by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id t8G3x4iA061706
 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO);
 Wed, 16 Sep 2015 06:59:05 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua t8G3x4iA061706
Received: (from kostik@localhost)
 by tom.home (8.15.2/8.15.2/Submit) id t8G3x4Rj061705;
 Wed, 16 Sep 2015 06:59:04 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com
 using -f
Date: Wed, 16 Sep 2015 06:59:04 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Andriy Gapon <avg@FreeBSD.org>
Cc: Dieter BSD <dieterbsd@gmail.com>, freebsd-hardware@FreeBSD.org,
 freebsd-hackers@FreeBSD.org
Subject: Re: ECC support
Message-ID: <20150916035904.GE67105@kib.kiev.ua>
References: <CAA3ZYrBXZn1WpHWYGJYWJDPsk7iDahCas8RhnHC4w+abf4w4hA@mail.gmail.com>
 <55F88A18.6090504@FreeBSD.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <55F88A18.6090504@FreeBSD.org>
User-Agent: Mutt/1.5.24 (2015-08-30)
X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00,
 DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no
 autolearn_force=no version=3.4.1
X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.20
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 16 Sep 2015 03:59:15 -0000

On Wed, Sep 16, 2015 at 12:14:00AM +0300, Andriy Gapon wrote:
> On 15/09/2015 23:53, Dieter BSD wrote:
> > Assuming that a board does have the necessary connections but
> > the firmware does not have ECC support, is there some reason that
> > ECC support could not be added to the OS instead of the firmware?
> 
> Yes, there is.  The memory controller is programmed by the code that runs from
> ROM and uses no RAM (or the CPU cache is used as the RAM).  Once the real RAM
> gets used it's too late to reprogram the DRAM controller.  This is true at least
> for most or all of the modern day x86 hardware.

For modern Intel hardware, the IMC config is locked before BIOS passes
the control to the user code, i.e. OS loader. It does not help much that
the documentation for IMC is not provided even under NDA.