linux-kernel - Re: [PATCH v7 3/8] arm64: introduce is_device_dma

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Message-ID: <alpine.DEB.2.02.1411101240290.22875@kaball.uk.xensource.com>
Date:	Mon, 10 Nov 2014 12:41:58 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"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>
Subject: Re: [PATCH v7 3/8] arm64: introduce is_device_dma_coherent

On Mon, 10 Nov 2014, Stefano Stabellini wrote:
> > BTW, pfn_valid() is more expensive than simply comparing the mfn with
> > pfn for dom0. The calling code knows this already and it may be quicker
> > to simply pass a "bool foreign" argument.
> 
> Good point, I can compare mfn and pfn here.
> I cannot do the same in unmap_page and the various sync operations,
> because there is no pfn available, but maybe I could use
> set_page_private to set a flag. I'll think about it.

But of course there is no struct page either so I think pfn_valid will
have to stay in unmap and sync
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