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

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Date:	Thu, 22 Sep 2011 16:48:27 +0300
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	"Roedel, Joerg" <Joerg.Roedel@....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 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.

That's why DRM_RADEON_KMS selects BACKLIGHT_CLASS_DEVICE; it's an
implementation detail that the user should not need to care about. Why
should I need to go see the dependencies of DRM_RADEON_KMS and
manually select all of them? I shouldn't, that's the reason 'select'
exists in the first place.

Cheers.

-- 
Felipe Contreras
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