[PATCH 0/1][SRU][Focal] Workaround for FLR bug in AMD Startship/Matisse USB and HD audio controllers

[Marcos Scriven]

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1865988

[Impact] 

The USB and HD audio controllers on 3rd-gen AMD Ryzen and Threadripper CPUs 
advertise Function Level Reset.

However, after invoking this the CPU becomes unstable and within minutes crashes

[Test Case]

 Requires a machine with a 3rd-gen Ryzen or Threadripper

 Invoke FLR on either of the affected CPU-provided controllers. For example, if lspci shows:

 	0d:00.3 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Matisse USB 3.0 Host Controller [1022:149c]
	0d:00.4 Audio device [0403]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse HD Audio Controller [1022:1487]


Then either of these will precipitate the issue:

  echo "1" > /sys/bus/pci/devices/0000:0d:00.3/reset
  echo "1" > /sys/bus/pci/devices/0000:0d:00.4/reset

[Regression Potential] 

This is a new workaround.

[Other Info]

The main users of this FLR functionality are those that wish to passthrough the USB or HD audio controllers to
a virtual machine from a Linux host.


Marcos Scriven (1):
  PCI: Avoid FLR for AMD Matisse HD Audio & USB 3.0

 drivers/pci/quirks.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

-- 
2.25.1