linux-kernel - Re: [RFC PATCH 6/6] sparc64: Enable 64-bit DMA

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Date:   Fri, 7 Oct 2016 01:09:15 -0700
From:   tndave <tushar.n.dave@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     davem@...emloft.net, chris.hyser@...cle.com,
        sowmini.varadhan@...cle.com, vgupta@...opsys.com,
        robin.murphy@....com, jroedel@...e.de, egtvedt@...fundet.no,
        krzk@...nel.org, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 6/6] sparc64: Enable 64-bit DMA



On 10/07/2016 12:32 AM, Christoph Hellwig wrote:
> On Thu, Oct 06, 2016 at 04:33:36PM -0700, Tushar Dave wrote:
>> ATU 64bit addressing allows PCIe devices with 64bit DMA capabilities
>> to use ATU for 64bit DMA.
>
> Any chance to always enable this?  Last I checked sparc was the only
> architecture still using a 32-bit dma_addr_t, leading to some fun
> breakage in things like the software RDMA drivers that abuse it to
> store a kernel pointer..
With change made by patch 6/6, dma_addr_t is always 64-bit, no matter if
device DMA mask is 32-bit (i.e. using existing IOMMU) or 64-bit (i.e
using ATU)

-Tushar

>