linux-kernel - Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu

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Message-ID: <20120125.093932.783007031082378997.hdoyu@nvidia.com>
Date:	Wed, 25 Jan 2012 08:39:32 +0100
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"joro@...tes.org" <joro@...tes.org>
CC:	"balbi@...com" <balbi@...com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver

From: "joro@...tes.org" <joro@...tes.org>
Subject: Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver
Date: Tue, 24 Jan 2012 15:25:21 +0100
Message-ID: <20120124142521.GE6269@...tes.org>

> On Tue, Jan 24, 2012 at 03:46:01PM +0200, Felipe Balbi wrote:
> > On Tue, Jan 24, 2012 at 02:41:21PM +0100, Hiroshi Doyu wrote:
> > > Actually I really like the concept of this "domain" now, which hides
> > > the H/W hierarchy from users.
> > > 
> > > But in Tegra SMMU/GART case, there's a single one IOMMU device in the
> > > system. Keeping a iommu device list in a domain and iterating iommu
> > > device list in each iommu_ops seem to be so nice, but I'm afraid that
> > > this may be a bit too much when one already knows that there's only
> > > one IOMMU device in the system.
> > >
> > > If there's no actual problem for 1-1 mapping between IOMMU H/Ws and
> > > domains, I think that it may not so bad to keep the original code(1-1)
> > > for GART and SMMU. What do you think?
> > 
> > I think it boils down to "extensability". If you can truly/fully
> > guarantee that there will *always* be a single IOMMU on all upcoming
> > Tegras, then it's really overkill.
> > 
> > But if there's even a remote possibility of the HW being changed and you
> > end up with more IOMMUs, things start to feel necessary for the sake of
> > making it easy to extend.
> 
> Right. But I am fine with the logic as-is when there is only one SMMU in
> the system. But please also change the IOMMU driver so that it really
> only initializes a single SMMU. When boards pop up with more than one
> you we notice that assumption in the code again and are reminded to
> change it.

Fixed.

I'll revisit 4MB pagesize support and the above multiple iommu device
support in a domain later.

Attached the update patch.

View attachment "0002-ARM-IOMMU-Tegra30-Add-iommu_ops-for-SMMU-driver.patch" of type "text/x-patch" (33838 bytes)