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

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Date:	Tue, 20 Sep 2011 12:54:38 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	"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

Hi Joerg,

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 :-)

> Further selecting whole drivers implicitly isn't a good idea. This can
> grow out of control very quickly.

-- 
Regards,

Laurent Pinchart
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