linux-kernel - Re: [PATCH] MIPS: Fix `dma_alloc_coherent' returning a non-coherent allocation

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Date:   Thu, 1 Nov 2018 09:33:46 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:     Christoph Hellwig <hch@....de>, Paul Burton <paul.burton@...s.com>,
        iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] MIPS: Fix `dma_alloc_coherent' returning a
 non-coherent allocation

On Thu, Nov 01, 2018 at 07:54:24AM +0000, Maciej W. Rozycki wrote:
> Fix a MIPS `dma_alloc_coherent' regression from commit bc3ec75de545 
> ("dma-mapping: merge direct and noncoherent ops") that causes a cached 
> allocation to be returned on noncoherent cache systems.
> 
> This is due to an inverted check now used in the MIPS implementation of 
> `arch_dma_alloc' on the result from `dma_direct_alloc_pages' before 
> doing the cached-to-uncached mapping of the allocation address obtained.  
> The mapping has to be done for a non-NULL rather than NULL result, 
> because a NULL result means the allocation has failed.
> 
> Invert the check for correct operation then.
> 
> Signed-off-by: Maciej W. Rozycki <macro@...ux-mips.org>
> Fixes: bc3ec75de545 ("dma-mapping: merge direct and noncoherent ops")
> Cc: stable@...r.kernel.org # 4.19+

Oops, yes this looks good:

Reviewed-by: Christoph Hellwig <hch@....de>