From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <benh@kernel.crashing.org>
Received: from gate.crashing.org (gate.crashing.org [63.228.1.57])
 (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
 (Client did not present a certificate)
 by ozlabs.org (Postfix) with ESMTPS id 7334F2C0095
 for <linuxppc-dev@lists.ozlabs.org>; Tue, 24 Jul 2012 13:08:48 +1000 (EST)
Message-ID: <1343099318.3715.0.camel@pasglop>
Subject: Re: [PATCH] powerpc/mm: add ZONE_NORMAL zone for 64 bit kernel
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Timur Tabi <timur@freescale.com>
Date: Tue, 24 Jul 2012 13:08:38 +1000
In-Reply-To: <500DDFF3.3000408@freescale.com>
References: <1342786906-12634-1-git-send-email-Shaohui.Xie@freescale.com>
 <1343023569.2957.19.camel@pasglop>	<500D7921.6060804@freescale.com>
 <1343082030.2957.38.camel@pasglop>
 <CAOZdJXXd6GuLAed_Z4zNMjDN+DBBXHdd0yVRHof+BJ_eiUMbqQ@mail.gmail.com>
 <1343085145.2957.44.camel@pasglop> <500DDB1B.9030900@freescale.com>
 <1343086186.2957.46.camel@pasglop> <500DDFF3.3000408@freescale.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Cc: Wood Scott-B07421 <B07421@freescale.com>,
 Hu Mingkai-B21284 <B21284@freescale.com>,
 "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
 Xie Shaohui-B21989 <B21989@freescale.com>,
 Chen Yuanquan-B41889 <B41889@freescale.com>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On Mon, 2012-07-23 at 18:36 -0500, Timur Tabi wrote:
> The DMA zone only kicks in if the DMA mask is set to a size smaller
> that
> available physical memory.  Sane HW should set the DMA mask to
> DMA_BIT_MASK(36).  And we have plenty of sane HW on our SOCs, but not
> every device is like that.
> 
> The whole point behind this patch is that some drivers are setting a
> DMA
> mask of 32, but still getting memory above 4GB.

Sure but I don't want to create the zones in the first place (and thus
introduce the added pressure on the memory management) on machines that
don't need it.

Cheers,
Ben.