linux-kernel - Re: [PATCH 11/33] dma-mapping: move swiotlb arch helpers to a new header

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Message-ID: <3721b4ba-0685-255e-06b9-6e60678a1a92@arm.com>
Date:   Wed, 10 Jan 2018 14:56:01 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org
Cc:     linux-mips@...ux-mips.org, linux-ia64@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        Guan Xuetao <gxt@...c.pku.edu.cn>, linux-arch@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-c6x-dev@...ux-c6x.org,
        linux-hexagon@...r.kernel.org, x86@...nel.org,
        Konrad Rzeszutek Wilk <konrad@...nok.org>,
        linux-snps-arc@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, patches@...ups.riscv.org,
        linux-metag@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Michal Simek <monstr@...str.eu>, linux-parisc@...r.kernel.org,
        linux-cris-kernel@...s.com, linux-kernel@...r.kernel.org,
        linux-alpha@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 11/33] dma-mapping: move swiotlb arch helpers to a new
 header

On 10/01/18 08:00, Christoph Hellwig wrote:
> phys_to_dma, dma_to_phys and dma_capable are helpers published by
> architecture code for use of swiotlb and xen-swiotlb only.  Drivers are
> not supposed to use these directly, but use the DMA API instead.
> 
> Move these to a new asm/dma-direct.h helper, included by a
> linux/dma-direct.h wrapper that provides the default linear mapping
> unless the architecture wants to override it.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
[...]
>   drivers/crypto/marvell/cesa.c                      |  1 +
>   drivers/mtd/nand/qcom_nandc.c                      |  1 +

I took a look at these, and it seems their phys_to_dma() usage is doing 
the thing which we subsequently formalised as dma_map_resource(). I've 
had a crack at a quick patch to update the CESA driver; qcom_nandc looks 
slightly more complex in that the changes probably need to span the BAM 
dmaengine driver as well.

In the process, though, I stumbled across gen_pool_dma_alloc() - yuck, 
something needs doing there, for sure...

Robin.