linux-kernel - Re: [PATCH 0/2] Fix incorrect warning from dma-debug

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Message-ID: <477ded30-eef2-3598-3a8d-95d206e11efb@jonmasters.org>
Date:   Sat, 6 May 2017 20:06:46 -0400
From:   Jon Masters <jcm@...masters.org>
To:     Robin Murphy <robin.murphy@....com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, dmaengine@...r.kernel.org
Cc:     linux-renesas-soc@...r.kernel.org, will.deacon@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fix incorrect warning from dma-debug

On 05/09/2016 06:00 AM, Robin Murphy wrote:
> On 09/05/16 10:37, Robin Murphy wrote:
>> Hi Niklas,
>>
>> On 08/05/16 11:59, Niklas Söderlund wrote:
>>> Hi,
>>>
>>> While using CONFIG_DMA_API_DEBUG i came across this warning which I
>>> think is a false positive. As shown dma_sync_single_for_device() are
>>> called from the dma_map_single() call path. This triggers the warning
>>> since the dma-debug code have not yet been made aware of the mapping.
>>
>> Almost right ;) The thing being mapped (the SPI device's buffer) and the
>> thing being synced (the IOMMU's PTE) are entirely unrelated. Due to the
>> current of_iommu_init() setup, the IOMMU is probed long before
>> dma_debug_init() gets called, therefore DMA debug is missing entries for
>> some of the initial page table mappings and gets confused when we update
>> them later.

What was the eventual followup/fix for this? We're seeing similar traces
to this during internal testing of 4.11 kernels.

Jon.

-- 
Computer Architect