linux-kernel - Re: [PATCH 2/2] iommu: Implement a dummy bus_set

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Message-ID: <20141015091043.GA13162@ulmo>
Date:	Wed, 15 Oct 2014 11:10:44 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iommu: Implement a dummy bus_set_iommu()

On Mon, Aug 18, 2014 at 06:57:50PM +0200, Joerg Roedel wrote:
> On Fri, Aug 01, 2014 at 02:45:13PM +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding@...dia.com>
> > 
> > This allows IOMMU drivers to compile even if IOMMU_API is not selected
> > and helps improve compile coverage.
> 
> IOMMU drivers usually implement the IOMMU-API, so they have a strong
> dependency to it. Why do you want to compile-test an iommu driver
> without testing the iommu core-code as well?

It seems like I never got back to you on this. The reason here is that
for Tegra the IOMMU is part of a larger IP block. The IP block is
primarily a memory controller with a bunch of configuration knobs for
arbitration, prioritization and whatnot. A smaller part of the device
does the IOMMU translation. Therefore the IOMMU implementation would
be part of a larger driver, and having this dummy would reduce the
amount of #ifdefs required.

bus_set_iommu() is also the only function in include/linux/iommu.h that
doesn't have a dummy, so it seemed like a natural thing to do.

That said, I can work around this being absent for !IOMMU_API.

Thierry

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