linux-kernel - Re: [PATCH v8 08/19] arm/xen: get_dma_ops: return xen_dma_ops if we are running as xen_initial

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Message-ID: <alpine.DEB.2.02.1310181643260.26077@kaball.uk.xensource.com>
Date:	Fri, 18 Oct 2013 16:46:00 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <konrad.wilk@...cle.com>,
	<Ian.Campbell@...rix.com>, <will.deacon@....com>
Subject: Re: [PATCH v8 08/19] arm/xen: get_dma_ops: return xen_dma_ops if we
 are running as xen_initial_domain

On Fri, 18 Oct 2013, Russell King - ARM Linux wrote:
> On Fri, Oct 18, 2013 at 01:22:18PM +0100, Stefano Stabellini wrote:
> > Russell,
> > are you OK with this patch?
> 
> Only concern is why the change is soo large.
> 
> > > -static inline struct dma_map_ops *get_dma_ops(struct device *dev)
> > > +static inline struct dma_map_ops *__generic_dma_ops(struct device *dev)
> > >  {
> > >  	if (dev && dev->archdata.dma_ops)
> > >  		return dev->archdata.dma_ops;
> > >  	return &arm_dma_ops;
> > >  }
> > >  
> > > +static inline struct dma_map_ops *get_dma_ops(struct device *dev)
> > > +{
> > > +	if (xen_initial_domain())
> > > +		return xen_dma_ops;
> > > +	else
> > > +		return __generic_dma_ops(dev);
> > > +}
> > > +
> 
> What's wrong with:
> 
>  static inline struct dma_map_ops *get_dma_ops(struct device *dev)
>  {
> +	if (xen_initial_domain())
> +		return xen_dma_ops;
>  	if (dev && dev->archdata.dma_ops)
>  		return dev->archdata.dma_ops;
>  	return &arm_dma_ops;
>  }


xen_dma_ops functions might have to call back the native implementation.
With the above there is no way for a xen_dma_ops function to get to
archdata.dma_ops or arm_dma_ops.
This is the reason why this patch introduces __generic_dma_ops.
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