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

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Message-ID: <20170307191201.645d23b4@free-electrons.com>
Date:   Tue, 7 Mar 2017 19:12:01 +0100
From:   Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:     David Laight <David.Laight@...LAB.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

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?

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com