linux-kernel - Re: [PATCH] iommu/dma-iommu: properly respect configured address space size

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Message-ID: <20161110155938.GI2078@8bytes.org>
Date:   Thu, 10 Nov 2016 16:59:39 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] iommu/dma-iommu: properly respect configured address
 space size

On Tue, Nov 08, 2016 at 11:37:23AM +0000, Robin Murphy wrote:
> TBH I've been pondering ripping the size stuff out of dma-iommu, as it
> all stems from me originally failing to understand what dma_32bit_pfn is
> actually for.

The point of dma_32bit_pfn is to allocate dma-address below 4G by
default. This is a performance optimization so that even devices capable
of 64bit DMA are using SAC by default instead of DAC.

Since it is the goal to share a dma-iommu implemenation between
architectures, I would rather prefer not to rip this stuff out.

	Joerg