linux-kernel - Re: [RFC] enhancing the kernel's graphics subsystem

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Date:	Mon, 21 May 2007 11:09:04 +0200
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	Dave Airlie <airlied@...il.com>
CC:	Jon Smirl <jonsmirl@...izon.net>,
	Jesse Barnes <jesse.barnes@...el.com>, jonsmirl@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] enhancing the kernel's graphics subsystem

Dave Airlie wrote:
> On 5/21/07, Jon Smirl <jonsmirl@...izon.net> wrote:
>> On Thu, 17 May 2007 14:23:45 -0700, Jesse Barnes wrote:
>>
>> > In collaboration with the FB guys, we've been working on enhancing the
>> > kernel's graphics subsystem in an attempt to bring some sanity to the
>> > Linux graphics world and avoid the situation we have now where several
>> > kernel and userspace drivers compete for control of graphics devices.
>>
>> How is supporting different users logged into each head going to work?
>> The original model for this was to give each head its own fbdev device.
>> It is important that each user be able to set their own mode without 
>> being
>> root.
>
> TThe problem with that is the concept of heads is flawed... there is
> in reality no such
> thing, you have crtcs and outputs, no heads. So any attempt to enforce
> the head concept involves putting policy into the kernel, as if I have
> 3 outputs but 2 crtcs how do I decide the mappings without the admin
> telling the kernel,
>
Solution:
One device per crtc. You can then have two users, running consoles
or xservers on their crtcs, without having to involve root.

The crtc->output mapping must still be done by root of course.

This solution allow the useful case where the computer boots, the boot 
scripts
set up a crtc->output mapping. Then users log in through the
various consoles (using getty or xdm or similiar) using their grahphical
devices in whatever way they want.  A true multiseat setup.


And if one user needs to use all the screens for multi-display work?
Let root change the mappings, possibly through some sudo setup.

Helge Hafting
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