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

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Date:   Sat, 24 Mar 2018 18:03:51 +0100
From:   Christoph Hellwig <hch@....de>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, 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 02:57:07PM -0400, Konrad Rzeszutek Wilk wrote:
> 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?


IFF we build swiotlb.c only for xen-swiotlb we don't need DMA_DIRECT_OPS.
IF you are fine with just requring it as well that would be doable nicely
only if we consolidate to a single defintion of CONFIG_SWIOTLB instead
of one per architecture.  Which is something we should do anyway,
so I'll look into it once I get some time.