linux-kernel - Re: [PATCH v4 3/7] [RFC] arm/arm64: introduce is_dma

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Message-ID: <20141013125725.GA19156@arm.com>
Date:	Mon, 13 Oct 2014 13:57:25 +0100
From:	Will Deacon <will.deacon@....com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH v4 3/7] [RFC] arm/arm64: introduce is_dma_coherent

On Mon, Oct 13, 2014 at 12:16:14PM +0100, Stefano Stabellini wrote:
> On Fri, 10 Oct 2014, Stefano Stabellini wrote:
> > On Fri, 10 Oct 2014, Will Deacon wrote:
> > > On Fri, Oct 10, 2014 at 12:51:44PM +0100, Stefano Stabellini wrote:
> > > > Introduce a function to check whether a device is dma coherent.
> > > > 
> > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > > > CC: linux@....linux.org.uk
> > > > CC: catalin.marinas@....com
> > > > CC: will.deacon@....com
> > > > CC: linux-arm-kernel@...ts.infradead.org
> > > > ---
> > > >  arch/arm/include/asm/dma-mapping.h   |    6 ++++++
> > > >  arch/arm64/include/asm/dma-mapping.h |    5 +++++
> > > >  2 files changed, 11 insertions(+)
> > > > 
> > > > diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> > > > index c45b61a..bededbb 100644
> > > > --- a/arch/arm/include/asm/dma-mapping.h
> > > > +++ b/arch/arm/include/asm/dma-mapping.h
> > > > @@ -126,6 +126,12 @@ static inline int set_arch_dma_coherent_ops(struct device *dev)
> > > >  	set_dma_ops(dev, &arm_coherent_dma_ops);
> > > >  	return 0;
> > > >  }
> > > > +
> > > > +static inline bool is_dma_coherent(struct device *dev)
> > > > +{
> > > > +    return (__generic_dma_ops(dev) == &arm_coherent_dma_ops);
> > > > +}
> > > 
> > > Hmm, what about the IOMMU ops?
> > 
> > Maybe I should check __generic_dma_ops(dev) != &arm_dma_ops?
> > Do you have any better suggestions?
> 
> ping?

Without any clear idea about why this is needed or how it's used, I don't
have any better ideas.

Will
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