netdev - RE: [PATCHv3 net-next 21/22] net: mvpp2: set dma mask and coherent dma mask on PPv2.2

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Date:   Wed, 8 Mar 2017 11:00:10 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Thomas Petazzoni' <thomas.petazzoni@...e-electrons.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Pawel Moll <pawel.moll@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        Kumar Gala <galak@...eaurora.org>,
        "Nadav Haklai" <nadavh@...vell.com>,
        Hanna Hawa <hannah@...vell.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Stefan Chulski <stefanc@...vell.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Russell King <linux@....linux.org.uk>
Subject: RE: [PATCHv3 net-next 21/22] net: mvpp2: set dma mask and coherent
 dma mask on PPv2.2

From: Thomas Petazzoni
> Sent: 07 March 2017 18:12
> Hello,
> 
> On Tue, 7 Mar 2017 17:24:21 +0000, David Laight wrote:
> 
> > Are the coherent mappings just used for ring structures?
> > If it might be reasonable to allocate them as a single entity,
> > thus guaranteeing they all reside in a single 4G region.
> 
> Do we have the guarantee that a DMA coherent allocation will not span a
> 4G boundary?

I'm pretty sure they are guaranteed not to cross any boundary they don't have to.
So a 16k buffer won't cross a 16k boundary.

	David