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SubjectRe: [PATCH] vga: implements VGA arbitration on Linux
On Tue, 11 Aug 2009 15:52:06 +1000
Dave Airlie <> wrote:

> From: Tiago Vignatti <>
> Background:
> Graphic devices are accessed through ranges in I/O or memory space.
> While most modern devices allow relocation of such ranges, some
> "Legacy" VGA devices implemented on PCI will typically have the same
> "hard-decoded" addresses as they did on ISA. For more details see
> "PCI Bus Binding to IEEE Std 1275-1994 Standard for Boot
> (Initialization Configuration) Firmware Revision 2.1" Section 7,
> Legacy Devices.
> The Resource Access Control (RAC) module inside the X server
> currently does the task of arbitration when more than one legacy
> device co-exists on the same machine. But the problem happens when
> these devices are trying to be accessed by different userspace
> clients (e.g. two server in parallel). Their address assignments
> conflict. Therefore an arbitration scheme _outside_ of the X server
> is needed to control the sharing of these resources. This document
> introduces the operation of the VGA arbiter implemented for Linux
> kernel.
> Signed-off-by: Tiago Vignatti <>
> Signed-off-by: Dave Airlie <>

Ok, applied this to my linux-next branch, but I'd like to get Ben's
s-o-b before pushing it to Linus.


Jesse Barnes, Intel Open Source Technology Center

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