linux-kernel - Re: [PATCH 2/2] iommu/io-pgtable-arm: use __dma_sync_single_for

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Message-ID: <20160509093540.GF19763@arm.com>
Date:	Mon, 9 May 2016 10:35:41 +0100
From:	Will Deacon <will.deacon@....com>
To:	Niklas Söderlund 
	<niklas.soderlund+renesas@...natech.se>
Cc:	linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux-foundation.org, dmaengine@...r.kernel.org,
	joro@...tes.org, linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, robin.murphy@....com
Subject: Re: [PATCH 2/2] iommu/io-pgtable-arm: use
 __dma_sync_single_for_device()

On Sun, May 08, 2016 at 12:59:56PM +0200, Niklas Söderlund wrote:
> The call to dma_sync_single_for_device() can be reached from
> dma_map_single(). If CONFIG_DMA_API_DEBUG is enabled this would result
> in a check that the mapping being synced is valid. Since the call to
> dma_map_single is not yet completed the mapping is not recorded in
> dma-debug and the check fails and a warning is printed. Avoid this
> warning by calling __dma_sync_single_for_device() which don't preform
> this check.

Hmm, I don't understand why this would trigger that warning. The memory
being sync'd here is the page table memory, not the buffer being mapped.
The page table memory is "mapped" using dma_map_single in
__arm_lpae_alloc_pages, so it sounds like the issue something else.

Will