On 38+ Intel-based ASUS products, the NVIDIA GPU becomes unusable after S3
suspend/resume.  The affected products include multiple generations of
NVIDIA GPUs and Intel SoCs.  After resume, nouveau logs many errors such
as:

  fifo: fault 00 [READ] at 0000005555555000 engine 00 [GR] client 04
        [HUB/FE] reason 4a [] on channel -1 [007fa91000 unknown]
  DRM: failed to idle channel 0 [DRM]

Similarly, the NVIDIA proprietary driver also fails after resume (black
screen, 100% CPU usage in Xorg process).  We shipped a sample to NVIDIA for
diagnosis, and their response indicated that it's a problem with the parent
PCI bridge (on the Intel SoC), not the GPU.

Runtime suspend/resume works fine, only S3 suspend is affected.

We found a workaround: on resume, rewrite the Intel PCI bridge
'Prefetchable Base Upper 32 Bits' register (PCI_PREF_BASE_UPPER32).  In the
cases that I checked, this register has value 0 and we just have to rewrite
that value.

Linux already saves and restores PCI config space during suspend/resume,
but this register was being skipped because upon resume, it already has
value 0 (the correct, pre-suspend value).

Intel appear to have previously acknowledged this behaviour and the
requirement to rewrite this register:
https://bugzilla.kernel.org/show_bug.cgi?id=116851#c23

Based on that, rewrite the prefetch register values even when that appears
unnecessary.

We have confirmed this solution on all the affected models we have in-hands
(X542UQ, UX533FD, X530UN, V272UN).

Additionally, this solves an issue where r8169 MSI-X interrupts were broken
after S3 suspend/resume on ASUS X441UAR.  This issue was recently worked
around in commit 7bb05b85 ("r8169: don't use MSI-X on RTL8106e").  It
also fixes the same issue on RTL6186evl/8111evl on an Aimfor-tech laptop
that we had not yet patched.  I suspect it will also fix the issue that was
worked around in commit 7c53a722 ("r8169: don't use MSI-X on
RTL8168g").

Thomas Martitz reports that this change also solves an issue where the AMD
Radeon Polaris 10 GPU on the HP Zbook 14u G5 is unresponsive after S3
suspend/resume.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=201069Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-By: Peter Wu <peter@lekensteyn.nl>
CC: stable@vger.kernel.org