[PATCH 1/1] PCI: Reprogram bridge prefetch registers on resume

[Kai-Heng Feng]

From: Daniel Drake <drake at endlessm.com>

BugLink: https://bugs.launchpad.net/bugs/1793338

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 7bb05b85bc2d ("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 7c53a722459c ("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=201069
Signed-off-by: Daniel Drake <drake at endlessm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Reviewed-By: Peter Wu <peter at lekensteyn.nl>
(cherry picked from commit 04cb3ae895d7efdc60f0fe17182b200a3da20f09 git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git pci/enumeration)
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
 drivers/pci/pci.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index f953042c7cdf..7e600b75d186 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1113,12 +1113,12 @@ int pci_save_state(struct pci_dev *dev)
 EXPORT_SYMBOL(pci_save_state);
 
 static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
-				     u32 saved_val, int retry)
+				     u32 saved_val, int retry, bool force)
 {
 	u32 val;
 
 	pci_read_config_dword(pdev, offset, &val);
-	if (val == saved_val)
+	if (!force && val == saved_val)
 		return;
 
 	for (;;) {
@@ -1137,25 +1137,36 @@ static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
 }
 
 static void pci_restore_config_space_range(struct pci_dev *pdev,
-					   int start, int end, int retry)
+					   int start, int end, int retry,
+					   bool force)
 {
 	int index;
 
 	for (index = end; index >= start; index--)
 		pci_restore_config_dword(pdev, 4 * index,
 					 pdev->saved_config_space[index],
-					 retry);
+					 retry, force);
 }
 
 static void pci_restore_config_space(struct pci_dev *pdev)
 {
 	if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL) {
-		pci_restore_config_space_range(pdev, 10, 15, 0);
+		pci_restore_config_space_range(pdev, 10, 15, 0, false);
 		/* Restore BARs before the command register. */
-		pci_restore_config_space_range(pdev, 4, 9, 10);
-		pci_restore_config_space_range(pdev, 0, 3, 0);
+		pci_restore_config_space_range(pdev, 4, 9, 10, false);
+		pci_restore_config_space_range(pdev, 0, 3, 0, false);
+	} else if (pdev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
+		pci_restore_config_space_range(pdev, 12, 15, 0, false);
+
+		/*
+		 * Force rewriting of prefetch registers to avoid S3 resume
+		 * issues on Intel PCI bridges that occur when these
+		 * registers are not explicitly written.
+		 */
+		pci_restore_config_space_range(pdev, 9, 11, 0, true);
+		pci_restore_config_space_range(pdev, 0, 8, 0, false);
 	} else {
-		pci_restore_config_space_range(pdev, 0, 15, 0);
+		pci_restore_config_space_range(pdev, 0, 15, 0, false);
 	}
 }
 
-- 
2.17.1