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

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Date:   Fri, 23 Mar 2018 20:41:37 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
cc:     Christoph Hellwig <hch@....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, 23 Mar 2018, 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?

You only want to do that when you actually need the code. If not it's a
pointless exercise.

But Christoph change makes sense independent of that because the next
oddball Kconfig will come along sooner than later and run into the very
same problem.

Thanks,

	tglx