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: <063D6719AE5E284EB5DD2968C1650D6DCFE79D2E@AcuExch.aculab.com>
Date:   Tue, 7 Mar 2017 17:24:21 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Thomas Petazzoni' <thomas.petazzoni@...e-electrons.com>,
        "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>
CC:     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 15:53
> On PPv2.2, the streaming mappings can be anywhere in the first 40 bits
> of the physical address space. However, for the coherent mappings, we
> still need them to be in the first 32 bits of the address space,
> because all BM pools share a single register to store the high 32 bits
> of the BM pool address, which means all BM pools must be allocated in
> the same 4GB memory area.

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.

	David