Discussion about x-igd-opregion

[Zhang, Tina]

+ intel-gvt-dev at lists.freedesktop.org

From: Zhang, Tina
Sent: Thursday, April 26, 2018 1:54 PM
To: 'Alex Williamson' <alex.williamson at redhat.com>
Cc: Lv, Zhiyuan <zhiyuan.lv at intel.com>; Yuan, Hang <hang.yuan at intel.com>; Tian, Kevin <kevin.tian at intel.com>; Wang, Zhenyu Z <zhenyu.z.wang at intel.com>; Wang, Zhi A <zhi.a.wang at intel.com>; Zhang, Xiong Y <xiong.y.zhang at intel.com>; Du, Changbin <changbin.du at intel.com>
Subject: Discussion about x-igd-opregion

Hi Alex,

These days, more and more people are asking if it's possible to let GVT-g support dma-buf feature with OVMF. As we know that, simply enabling the BDSM fw_cfg entry in OVMF cannot solve the whole problem, as we are still basing on "x-igd-opregion=on" which is an experimental option. So, we'd like to use this thread to discuss the issue and find a solution for it.

Background:
The problem is in GVT-g, Windows guest needs opregion to touch display registers, which is key to GVT-g dma-buf display feature based on VFIO. This opregion is provided by an QEMU experimental option called "x-igd-opregion=on", which was introduced due to some interesting display usages for IGD UPT mode. But the UPT mode isn't invented to be used with display. That's why this opinion is called experimental x-option.

So, Alex, we saw that you have some comments about this issue before: "The feature cannot be considered supportable in libvirt until opregion support is either enabled automatically or enabled through a non-experimental option". Could you elaborate more on these two opinions?

We'd like to propose a solution to solve this issue between QEMU/VFIO and GVT-g. After all, as you know, it's not reasonable to let OVMF support opregion only for IGD UPT mode, as the legacy mode is missing and the UPT mode isn't defined to work with the help of a firmware.
Thanks.


Reference:
https://bugzilla.tianocore.org/show_bug.cgi?id=935
http://vfio.blogspot.com/2016/07/intel-graphics-assignment.html


BR,
Tina


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