linux-kernel - Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes as supported by the hardware

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Message-ID: <20111011101936.GD2138@amd.com>
Date:	Tue, 11 Oct 2011 12:19:36 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	David Brown <davidb@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Hiroshi Doyu <hdoyu@...dia.com>
Subject: Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes as
 supported by the hardware

Hi Ohad,

On Mon, Oct 10, 2011 at 01:02:46PM -0400, Ohad Ben-Cohen wrote:
> On Mon, Oct 10, 2011 at 5:36 PM, Roedel, Joerg <Joerg.Roedel@....com> wrote:
> > Yes, somthing like that. Probably the iommu_ops->unmap function should
> > be turned into a unmap_page function call which only takes an iova and
> > no size parameter. The iommu-driver unmaps the page pointing to that
> > iova and returns the size of the page unmapped. This still allows the
> > simple implementation for the unmap-call.
> 
> Yes, exactly. It will take some time to migrate all drivers (today we
> have 4 drivers, each of which is implementing a slightly different
> ->unmap() semantics), but at least let's not accept any new driver
> that doesn't adhere to this, otherwise it's going to be even harder
> for the API to evolve.

Agreed. We should change the existing drivers one-by-one.

> > We don't need to really enforce the calls to be symetric. But we can
> > define that we only give the guarantee about what will be unmapped
> > when the calls are symetric.
> 
> Sounds good to me. I'll add this to the kernel doc patch (which I'll
> submit after this patch set materializes), and when/if we move to
> symmetric only, we will update it.

Great. So if no one disagrees with this direction (this means all the
other people on Cc :) ) it is the way to.

	Joerg

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