Subject: Re: [PATCH 29/33] dma-direct: retry allocations using GFP_DMA for
 small masks
To: Christoph Hellwig <hch@lst.de>, iommu@lists.linux-foundation.org
Cc: linux-mips@linux-mips.org, linux-ia64@vger.kernel.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        Guan Xuetao <gxt@mprc.pku.edu.cn>, linux-arch@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org,
        linux-hexagon@vger.kernel.org, x86@kernel.org,
        Konrad Rzeszutek Wilk <konrad@darnok.org>,
        linux-snps-arc@lists.infradead.org,
        linux-m68k@lists.linux-m68k.org, patches@groups.riscv.org,
        linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Michal Simek <monstr@monstr.eu>, linux-parisc@vger.kernel.org,
        linux-cris-kernel@axis.com, linux-kernel@vger.kernel.org,
        linux-alpha@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <20180110080027.13879-1-hch@lst.de>
 <20180110080027.13879-30-hch@lst.de>
From: Vladimir Murzin <vladimir.murzin@arm.com>
Message-ID: <93966313-cc79-8173-48e6-157caa443322@arm.com>
Date: Wed, 10 Jan 2018 09:32:16 +0000
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On 10/01/18 08:00, Christoph Hellwig wrote:
> If an attempt to allocate memory succeeded, but isn't inside the
> supported DMA mask, retry the allocation with GFP_DMA set as a
> last resort.
> 
> Based on the x86 code, but an off by one error in what is now
> dma_coherent_ok has been fixed vs the x86 code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  lib/dma-direct.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/dma-direct.c b/lib/dma-direct.c
> index 8f76032ebc3c..4e43c2bb7f5f 100644
> --- a/lib/dma-direct.c
> +++ b/lib/dma-direct.c
> @@ -35,6 +35,11 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>  	return true;
>  }
>  
> +static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
> +{
> +	return phys_to_dma(dev, phys) + size - 1 <= dev->coherent_dma_mask;
> +}
> +
>  static void *dma_direct_alloc(struct device *dev, size_t size,
>  		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
>  {
> @@ -48,11 +53,29 @@ static void *dma_direct_alloc(struct device *dev, size_t size,
>  	if (dev->coherent_dma_mask <= DMA_BIT_MASK(32) && !(gfp & GFP_DMA))
>  		gfp |= GFP_DMA32;
>  
> +again:
>  	/* CMA can be used only in the context which permits sleeping */
> -	if (gfpflags_allow_blocking(gfp))
> +	if (gfpflags_allow_blocking(gfp)) {
>  		page = dma_alloc_from_contiguous(dev, count, page_order, gfp);
> +		if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +			dma_release_from_contiguous(dev, page, count);
> +			page = NULL;
> +		}
> +	}
>  	if (!page)
>  		page = alloc_pages_node(dev_to_node(dev), gfp, page_order);
> +
> +	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +		__free_pages(page, page_order);
> +		page = NULL;
> +
> +		if (dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
> +		    !(gfp & GFP_DMA)) {
> +			gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
> +			goto again;
> +		}
> +	}
> +
>  	if (!page)
>  		return NULL;
>  
> 

Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>

Cheers
Vladimir