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Subject: Re: [RFC PATCH 0/4] Stop losing firmware-set DMA masks
To:     Christoph Hellwig <hch@lst.de>
Cc:     m.szyprowski@samsung.com, iommu@lists.linux-foundation.org,
        linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        lorenzo.pieralisi@arm.com, hanjun.guo@linaro.org,
        sudeep.holla@arm.com, robh+dt@kernel.org, frowand.list@gmail.com,
        gregkh@linuxfoundation.org, joro@8bytes.org, x86@kernel.org,
        Palmer Dabbelt <palmer@sifive.com>,
        linux-riscv@lists.infradead.org
References: <cover.1531239284.git.robin.murphy@arm.com>
 <20180710180232.GA26285@lst.de>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <89365af4-19fa-1dc2-27d0-37e9145134af@arm.com>
Date:   Tue, 10 Jul 2018 19:11:38 +0100
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On 10/07/18 19:02, Christoph Hellwig wrote:
>> These patches attempt to deal with this in the simplest way possible by
>> generalising the specific quirk for 32-bit bridges into an arbitrary
>> mask which can then also be plumbed into the firmware code. In the
>> interest of being minimally invasive, I've only included a point fix
>> for the IOMMU issue as seen on arm64 - there may be further tweaks
>> needed in DMA ops to catch all possible incarnations of this problem,
>> but this initial RFC is mostly about the impact beyond the dma-mapping
>> subsystem itself.
> 
> Thanks, this looks very nice to me.
> 
> In fact it probably solves the RISC-V/Xiling problem as well if we can
> just add the dma-ranges property to the device tree for the affected
> systems.  Palmer, do you know how easily the DT could be updated for
> that case?

That would indeed be nice, but beware that the way PCI devices are 
bodged through of_dma_configure() only actually works for dma-coherent 
and is busted WRT parsing dma-ranges correctly. Fixing that is my next 
step after getting these basics done ;)

Robin.