linux-kernel - Re: [RFC PATCH 0/4] Stop losing firmware-set DMA masks

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Date:   Tue, 10 Jul 2018 19:11:38 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     m.szyprowski@...sung.com, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        lorenzo.pieralisi@....com, hanjun.guo@...aro.org,
        sudeep.holla@....com, robh+dt@...nel.org, frowand.list@...il.com,
        gregkh@...uxfoundation.org, joro@...tes.org, x86@...nel.org,
        Palmer Dabbelt <palmer@...ive.com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [RFC PATCH 0/4] Stop losing firmware-set DMA masks

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.