From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752609AbcLYJEr (ORCPT <rfc822;w@1wt.eu>);
        Sun, 25 Dec 2016 04:04:47 -0500
Received: from mout.gmx.net ([212.227.15.19]:52095 "EHLO mout.gmx.net"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751282AbcLYJEi (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Sun, 25 Dec 2016 04:04:38 -0500
From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Alistair Popple <apopple@au1.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Bharata B Rao <bharata@linux.vnet.ibm.com>,
        Frank Rowand <frowand.list@gmail.com>, Ingo Molnar <mingo@redhat.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nathan Fontenot <nfont@linux.vnet.ibm.com>,
        Paul Mackerras <paulus@samba.org>, Rob Herring <robh+dt@kernel.org>,
        Stewart Smith <stewart@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Heinrich Schuchardt <xypron.glpk@gmx.de>
Subject: Re: [PATCH v6 4/4] of/fdt: mark hotpluggable memory
Date: Sun, 25 Dec 2016 10:02:22 +0100
Message-Id: <20161225090222.3703-1-xypron.glpk@gmx.de>
X-Mailer: git-send-email 2.11.0
In-Reply-To: <1478562276-25539-5-git-send-email-arbab@linux.vnet.ibm.com>
References: <1478562276-25539-5-git-send-email-arbab@linux.vnet.ibm.com>
X-Provags-ID: V03:K0:Ikq5EOYcZmF773V4bbO+ngjIq3ygkDMhEiD8mrkRYkPvelqx8eG
 67Bs9ul9o668tjuzenTCG/r26XTd7jne1q22afVnEokjPolus/mzUxtyOKFKqC4VEMw9i6w
 2unAJezEcxc0/JifAxg3czwhIzOJQsQM0dQ2YgbBk9k4ZSjnkiUIZmhwWcQn+Tlh+J8RKP6
 W9ckYAC/G5Kunc8AwW16A==
X-UI-Out-Filterresults: notjunk:1;V01:K0:TeRdA3QvYqs=:IAMgHA+3e+Wzf39t1D5CSQ
 fIP1mHpTH2o0L8YAv9YCFmCk26TtSh2FUeydyqgb18FalceYN05xaunLWBUvZuABbeDdnAFdo
 1ev+lv4pdnzEF+nuq5G5aBX5YEz66p6XPdDvaba3NWqfQt2XLacpMWdkc0hhZGrZVIYZ7/yt/
 WyX3CcWTafPDBVAq5xghdYaptdKfO4dIVIDjhun8Ph32gmQ06TcMXMg+tG7iWyjJmHtUGgZ4v
 F+PriUL9u9xpVqCZfL1W0VbbltjQMKNLsWGjBRU3FN9XfsqImrVMKu93DARQv5MSivdDDiL0/
 dqmFB3SR3SQPGGQTzsXIsg41KpQ9eRBWBq6v2QTmtVichxXLVJnPhtu/X+vK1xqx30iAdeGsQ
 3azdS3KDW1FHSrO+BwXvN71WUYcViQ3uf1o/Lp2WBPsHLheCrbRNnuxPjjqhhul4oBgZOGSHf
 dla9pvWis0ntx2wgby0vUDZbF3neUWLyHuDwfgI2wh0yEdDOpeNr6rc20OvPKMZuqxLNZzrGX
 2z5YJkUdY+gdZKP3/ZEEkj4QnYry8oc9j9IT6vpYgKRPyUICCoxesjmeu7QZvW15S4YNFiR9N
 I5hSf9C4ZyvgHvXgg1USSFhoRemVc0lDQYp/E+7W+TK9hIMgQeoEa1UC4QfrKRPk7EaPUCJzE
 F1hZmgzvRAMvGe2s1dBxDwJu6g72b9SMQ4EJPQTru6YsjBDGUGS/hWBgRJIURPyh6DNVMLwWI
 RqB5UvCk9U44eFFlYasTW7T17H7wFIevpjEgY6xCr9OuaSV/DO26nLPhP6c=
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

The patch adds a new property "linux,hotpluggable" to memory nodes of the
device tree.

memory@0 {
	reg = <0x0 0x01000000 0x0 0x7f000000>;
	linux,hotpluggable;
}

Memory areas marked by this property can later be disabled using the hotplugging
API. Especially for virtual machines this is a very useful capability.

Unfortunately the notation chosen does not fit well with the concept of
devicetree overlays which allow to change the devicetree during runtime.

I suggest to use the following notation

memory@0 {
	compatible = "linux,hotpluggable-memory";
	reg = <0x0 0x01000000 0x0 0x7f000000>;
	status = "disabled";
}

This will allow us to write a device driver that can react to changes of the
devicetree made via devicetree overlays.

This driver could react to the change of the status between "okay" and
"disabled" and update the memory status accordingly.

Further we could use devicetree overlays to provide additional hotpluggable
memory.

The referenced patch has already been pulled for 4.10. But I hope it is not
too late for this design change.

Best regards

Heinrich Schuchardt