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

From: Jon Masters
Date: Sat May 06 2017 - 20:07:22 EST

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 SÃderlund 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.


Computer Architect