linux-kernel - Re: [PATCH 2/5] iommu: Allocate a default domain for iommu groups

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Date:	Fri, 30 Jan 2015 13:25:30 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Kukjin Kim <kgene@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Robin Murphy <Robin.Murphy@....com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	"jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [PATCH 2/5] iommu: Allocate a default domain for iommu groups

On Wed, Jan 28, 2015 at 02:30:06PM +0000, Will Deacon wrote:
> On Tue, Jan 27, 2015 at 12:08:56AM +0000, Joerg Roedel wrote:
> > +	if (group->default_domain == NULL)
> > +		group->default_domain = __iommu_domain_alloc(dev->bus,
> > +							     IOMMU_DOMAIN_DMA);
> 
> Having a per-group domain is wasteful for IOMMUs that only support a modest
> number of concurrent domains, so in reality I think we need to have one
> domain per IOMMU instance. Is that possible?

Well, you could make sure that there are no more groups behind one IOMMU
than the number of concurent domains it can handle. But that would be
too static. But once we have an per-iommu-descriptor in the IOMMU core I
see no reason to allocate a default domain per iommu only, based on a
policy exported by the driver.


	Joerg

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