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[Qemu-devel] Debugging PCI Enhanced Allocation - IOMMU of a bridge?


From: Alexander von Gluck IV
Subject: [Qemu-devel] Debugging PCI Enhanced Allocation - IOMMU of a bridge?
Date: Wed, 12 Sep 2018 17:30:29 +0000

Good morning!

I'm working through adding support (or at least ignoring) PCI Enhance 
Allocation devices under Haiku.
We run into one of these devices, and crash at boot due to attempting to read 
an invalid address.

Our testing showed that with a USB C dongle plugged in, we don't crash. Without 
it plugged in we get
invalid addresses from PCI

(for a long-drawn out debug ticket, see https://dev.haiku-os.org/ticket/12885 )
So, i'm trying to see if I can emulate a PCI bridge with EA under QEMU, I found 
this patch, but it seems  it wasn't accepted:   
https://lists.gnu.org/archive/html/qemu-devel/2015-05/msg02073.html 
(https://lists.gnu.org/archive/html/qemu-devel/2015-05/msg02073.html)

My other thought is since I have access to two laptops implementing this, I 
could attach the bridge to
qemu via iommu, but the new vfio stuff doesn't seem to work with bridges. :-|   
Anyone know of a way to:  * emulate a PCI EA in qemu.  * attach the local PCI 
EA bridge to qemu to troubleshoot using real hardware.  For context, here is 
the suspect EA device:
(no USB C dongle)
$ lspci -tvnn
-[0000:00]-+-00.0 Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core 
Processor Host Bridge/DRAM Registers [8086:1910]
 +-1d.6-[06-3e]--

vs

(USB C dongle)
$ lspci -tvnn
-[0000:00]-+-00.0 Intel Corporation Skylake Host Bridge/DRAM Registers 
[8086:1904]
 +-1d.6-[06-3e]----00.0-[07-3e]--+-00.0-[08]--
 | +-01.0-[09-3d]--
 | -02.0-[3e]----00.0 Intel Corporation DSL6340 USB 3.1 Controller [Alpine 
Ridge] [8086:15b5]
The bride is at 1d.6 in it's own IOMMU group:

IOMMU group 12
 00:1d.6 PCI bridge [0604]: Intel Corporation 100 Series/C230 Series Chipset 
Family PCI Express Root Port #15 [8086:a11e] (rev f1)

 -- Alex


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