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

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Message-ID: <20180324200545.GC23658@char.us.oracle.com>
Date:   Sat, 24 Mar 2018 16:05:45 -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 Sat, Mar 24, 2018 at 06:03:51PM +0100, Christoph Hellwig wrote:
> 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.

I don't think there is ever an case where you want a Xen specific build.

> 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.

Sounds good. Thank you.