linux-kernel - Re: [PATCH] swiotlb: swiotlb_{alloc,free}_buffer should depend on CONFIG_DMA_DIRECT

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Date:   Fri, 23 Mar 2018 14:57:07 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     tglx@...utronix.de, mingo@...e.hu, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] swiotlb: swiotlb_{alloc,free}_buffer should depend on
 CONFIG_DMA_DIRECT_OPS

On Fri, Mar 23, 2018 at 06:49:30PM +0100, Christoph Hellwig wrote:
> Otherwise we might get unused symbol warnings for configs that built
> swiotlb.c only for use by xen-swiotlb.c and that don't otherwise select
> CONFIG_DMA_DIRECT_OPS, which is possible on arm.
> 
> Fixes: 16e73adbca76 ("dma/swiotlb: Remove swiotlb_{alloc,free}_coherent()")
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Christoph Hellwig <hch@....de>


Alternatively could we set the Kconfig to slect DMA_DIRECT_OPS?

> ---
>  lib/swiotlb.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 15954b86f09e..47aeb04c1997 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -692,6 +692,7 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
>  	}
>  }
>  
> +#ifdef CONFIG_DMA_DIRECT_OPS
>  static inline bool dma_coherent_ok(struct device *dev, dma_addr_t addr,
>  		size_t size)
>  {
> @@ -763,6 +764,7 @@ static bool swiotlb_free_buffer(struct device *dev, size_t size,
>  				 DMA_ATTR_SKIP_CPU_SYNC);
>  	return true;
>  }
> +#endif
>  
>  static void
>  swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
> -- 
> 2.14.2
>