linux-kernel - Re: [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required

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Message-ID: <02ce2ecc-281d-7b7f-6d30-8d246acd1eaa@arm.com>
Date:   Thu, 27 Sep 2018 15:12:25 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/5] dma-direct: add an explicit
 dma_direct_get_required_mask

On 20/09/18 19:52, Christoph Hellwig wrote:
> This is somewhat modelled after the powerpc version, and differs from
> the legacy fallback in use fls64 instead of pointlessly splitting up the
> address into low and high dwords and in that it takes (__)phys_to_dma
> into account.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   include/linux/dma-direct.h |  1 +
>   kernel/dma/direct.c        | 21 ++++++++++++++++++---
>   2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index 86a59ba5a7f3..b79496d8c75b 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -55,6 +55,7 @@ static inline void dma_mark_clean(void *addr, size_t size)
>   }
>   #endif /* CONFIG_ARCH_HAS_DMA_MARK_CLEAN */
>   
> +u64 dma_direct_get_required_mask(struct device *dev);
>   void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>   		gfp_t gfp, unsigned long attrs);
>   void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index c954f0a6dc62..81b73a5bba54 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -53,11 +53,25 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>   	return true;
>   }
>   
> +static inline dma_addr_t phys_to_dma_direct(struct device *dev,
> +		phys_addr_t phys)
> +{
> +	if (force_dma_unencrypted())
> +		return __phys_to_dma(dev, phys);
> +	return phys_to_dma(dev, phys);
> +}
> +
> +u64 dma_direct_get_required_mask(struct device *dev)
> +{
> +	u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
> +
> +	return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;

I think that may as well just use __fls64() - it seems reasonable to 
assume max_dma > 0. Otherwise,

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

> +}
> +
>   static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
>   {
> -	dma_addr_t addr = force_dma_unencrypted() ?
> -		__phys_to_dma(dev, phys) : phys_to_dma(dev, phys);
> -	return addr + size - 1 <= dev->coherent_dma_mask;
> +	return phys_to_dma_direct(dev, phys) + size - 1 <=
> +			dev->coherent_dma_mask;
>   }
>   
>   void *dma_direct_alloc_pages(struct device *dev, size_t size,
> @@ -296,6 +310,7 @@ const struct dma_map_ops dma_direct_ops = {
>   	.unmap_page		= dma_direct_unmap_page,
>   	.unmap_sg		= dma_direct_unmap_sg,
>   #endif
> +	.get_required_mask	= dma_direct_get_required_mask,
>   	.dma_supported		= dma_direct_supported,
>   	.mapping_error		= dma_direct_mapping_error,
>   	.cache_sync		= arch_dma_cache_sync,
>