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

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Date:   Tue, 10 Jul 2018 11:12:07 -0700
From:   Atish Patra <atish.patra@....com>
To:     Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        "hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "frowand.list@...il.com" <frowand.list@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>
Subject: Re: [RFC PATCH 0/4] Stop losing firmware-set DMA masks

On 7/10/18 11:01 AM, 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?
> 
Hi Chris,
I have a PR in riscv-pk that can modify the DT in bbl easily. In fact, 
that's how I added the timer node for the interrupt patch.

https://github.com/riscv/riscv-pk/pull/112

Obviously, the best approach would be to update the firmware but that 
may be time consuming sometime.

Regards,
Atish
>>
>> Robin.
>>
>>
>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/580804.html
>> [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-December/474443.html
>>
>> Robin Murphy (4):
>>    dma-mapping: Generalise dma_32bit_limit flag
>>    ACPI/IORT: Set bus DMA mask as appropriate
>>    of/device: Set bus DMA mask as appropriate
>>    iommu/dma: Respect bus DMA limit for IOVAs
>>
>>   arch/x86/kernel/pci-dma.c | 2 +-
>>   drivers/acpi/arm64/iort.c | 1 +
>>   drivers/iommu/dma-iommu.c | 3 +++
>>   drivers/of/device.c       | 1 +
>>   include/linux/device.h    | 6 +++---
>>   kernel/dma/direct.c       | 2 +-
>>   6 files changed, 10 insertions(+), 5 deletions(-)
>>
>> -- 
>> 2.17.1.dirty
> ---end quoted text---
> 
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