Date: Thu, 22 Jul 2010 09:28:20 -0700
From: Zach Pfeffer <zpfeffer@codeaurora.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>, ebiederm@xmission.com,
        linux-arch@vger.kernel.org, dwalker@codeaurora.org, mel@csn.ul.ie,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, andi@firstfloor.org, linux-omap@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device
 memory management
Message-ID: <20100722162818.GD10255@codeaurora.org>
References: <20100715014148.GC2239@codeaurora.org>
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 <20100720221959.GC12250@codeaurora.org>
 <20100721104356S.fujita.tomonori@lab.ntt.co.jp>
 <20100722043034.GC22559@codeaurora.org>
 <20100722073917.GC6802@n2100.arm.linux.org.uk>
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On Thu, Jul 22, 2010 at 08:39:17AM +0100, Russell King - ARM Linux wrote:
> On Wed, Jul 21, 2010 at 09:30:34PM -0700, Zach Pfeffer wrote:
> > This goes to the nub of the issue. We need a lot of 1 MB physically
> > contiguous chunks. The system is going to fragment and we'll never get
> > our 12 1 MB chunks that we'll need, since the DMA API allocator uses
> > the system pool it will never succeed.
> 
> By the "DMA API allocator" I assume you mean the coherent DMA interface,
> The DMA coherent API and DMA streaming APIs are two separate sub-interfaces
> of the DMA API and are not dependent on each other.

I didn't know that, but yes. As far as I can tell they both allocate
memory from the VM. We'd need a way to hook in our our own minimized
mapping allocator.
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