deb2d2ecd4
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: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Tiago Vignatti <tiago.vignatti@nokia.com> Signed-off-by: Dave Airlie <airlied@redhat.com> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org> |
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