linux-kernel - Re: refactor dma_cache

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Message-ID: <87817c6a-b03f-6da0-4e69-22ea68d44bd5@arm.com>
Date:   Tue, 3 Oct 2017 12:49:51 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Simek <monstr@...str.eu>,
        David Howells <dhowells@...hat.com>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
        linux-mips@...ux-mips.org, linux-ia64@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-xtensa@...ux-xtensa.org,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: refactor dma_cache_sync V2

On 03/10/17 11:43, Christoph Hellwig wrote:
> The dma_cache_sync routines is used to flush caches for memory returned
> by dma_alloc_attrs with the DMA_ATTR_NON_CONSISTENT flag (or previously
> from dma_alloc_noncoherent), but the requirements for it seems to be
> frequently misunderstood.  dma_cache_sync is documented to be a no-op for
> allocations that do not have the DMA_ATTR_NON_CONSISTENT flag set, and
> yet a lot of architectures implement it in some way despite not
> implementing DMA_ATTR_NON_CONSISTENT.
> 
> This series removes a few abuses of dma_cache_sync for non-DMA API
> purposes, then changes all remaining architectures that do not implement
> DMA_ATTR_NON_CONSISTENT to implement dma_cache_sync as a no-op, and
> then adds the struct dma_map_ops indirection we use for all other
> DMA mapping operations to dma_cache_sync as well, thus removing all but
> two implementations of the function.
> 
> Changes since V1:
>  - drop the mips fd_cacheflush, merged via maintainer
>  - spelling fix in last commit descriptions (thanks Geert)
> 

For the series,

Reviewed-by: Robin Murphy <robin.murphy@....com>

The MIPS DMA ops are a little fiddly, but I've satisfied myself that
CONFIG_DMA_NONCOHERENT and CONFIG_SWIOTLB are mutually exclusive for
Loongson64 such that patch #11 isn't missing anything.

Robin.