[PATCH V2] PCI/ASPM: Skip L1SS save/restore if not already enabled

[Vidya Sagar]

Skip save and restore of ASPM L1 Sub-States specific registers if they
are not already enabled in the system. This is to avoid issues observed
on certain platforms during restoration process, particularly when
restoring the L1SS registers contents.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=216782
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
---
v2:
* Address review comments from Kai-Heng Feng and Rafael

 drivers/pci/pcie/aspm.c | 17 ++++++++++++++++-
 include/linux/pci.h     |  1 +
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 53a1fa306e1e..bd2a922081bd 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -761,11 +761,23 @@ void pci_save_aspm_l1ss_state(struct pci_dev *dev)
 {
 	struct pci_cap_saved_state *save_state;
 	u16 l1ss = dev->l1ss;
-	u32 *cap;
+	u32 *cap, val;
 
 	if (!l1ss)
 		return;
 
+	/*
+	 * Skip save and restore of L1 Sub-States registers if they are not
+	 * already enabled in the system
+	 */
+	pci_read_config_dword(dev, l1ss + PCI_L1SS_CTL1, &val);
+	if (!(val & PCI_L1SS_CTL1_L1SS_MASK)) {
+		dev->skip_l1ss_restore = true;
+		return;
+	}
+
+	dev->skip_l1ss_restore = false;
+
 	save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
 	if (!save_state)
 		return;
@@ -784,6 +796,9 @@ void pci_restore_aspm_l1ss_state(struct pci_dev *dev)
 	if (!l1ss)
 		return;
 
+	if (dev->skip_l1ss_restore)
+		return;
+
 	save_state = pci_find_saved_ext_cap(dev, PCI_EXT_CAP_ID_L1SS);
 	if (!save_state)
 		return;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 22319ea71ab0..39534602b55e 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -395,6 +395,7 @@ struct pci_dev {
 	unsigned int	ltr_path:1;	/* Latency Tolerance Reporting
 					   supported from root to here */
 	u16		l1ss;		/* L1SS Capability pointer */
+	bool		skip_l1ss_restore;	/* Skip L1SS Save/Restore */
 #endif
 	unsigned int	pasid_no_tlp:1;		/* PASID works without TLP Prefix */
 	unsigned int	eetlp_prefix_path:1;	/* End-to-End TLP Prefix */
-- 
2.17.1