linux-kernel - Re: [PATCH] iommu/omap: Fix build error with !IOMMU

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Message-ID: <20110923090557.GB16329@amd.com>
Date:	Fri, 23 Sep 2011 11:05:57 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Felipe Contreras <felipe.contreras@...il.com>
CC:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/omap: Fix build error with !IOMMU_SUPPORT

On Thu, Sep 22, 2011 at 09:48:27AM -0400, Felipe Contreras wrote:
> On Tue, Sep 20, 2011 at 1:54 PM, Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
> > On Tuesday 20 September 2011 12:01:46 Roedel, Joerg wrote:
> >> On Sat, Sep 17, 2011 at 08:02:22PM -0400, Laurent Pinchart wrote:
> >> > On Wednesday 14 September 2011 16:07:39 Joerg Roedel wrote:
> >> > > Without this patch it is possible to select the VIDEO_OMAP3
> >> > > driver which then selects OMAP_IOVMM. But the omap iommu
> >> > > driver is not compiled without IOMMU_SUPPORT enabled. Fix
> >> > > that by forcing OMAP_IOMMU and OMAP_IOVMM are enabled before
> >> > > VIDEO_OMAP3 can be selected.
> >> >
> >> > What about making VIDEO_OMAP3 select IOMMU_SUPPORT instead then ? Your
> >> > patch would make the OMAP3 ISP driver disappear from the menu until
> >> > IOMMU_SUPPORT gets turned on, which can confuse users.
> >>
> >> Using 'depends on' rather then 'selects' is common standard in Kconfig.
> >> You can't select PCI drivers without selecting PCI first, for example.
> >
> > You wouldn't expect a PCI driver to work without PCI support. My concern is
> > that most OMAP3 ISP users won't know that IOMMU supports is required. Feel
> > free to ignore it though :-)
> 
> I agree with Laurent. As a user, why should I care about IOMMU? I just
> want this thing.

Because enabling IOMMU can have other side-effects on the system and as
a user you want to be aware that it is enabled. A user not wanting the
iommu driver can just disable it then without the need to de-select all
drivers depending on it first.

	Joerg

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