[PATCH v2 1/4] PCI: Check PCI_PM_CTRL in pci_dev_wait()

[superm1@kernel.org]

From: Mario Limonciello <mario.limonciello@amd.com>

A device that has gone through a reset may return a value in PCI_COMMAND
but that doesn't mean it's finished transitioning to D0.  On devices that
support power management explicitly check PCI_PM_CTRL on everything but
system resume to ensure the transition happened.

Devices that don't support power management and system resume will
continue to use PCI_COMMAND.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/pci/pci.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 35fb1f17a589c..4ad02ad640518 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1270,21 +1270,34 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 	 * the read (except when CRS SV is enabled and the read was for the
 	 * Vendor ID; in that case it synthesizes 0x0001 data).
 	 *
-	 * Wait for the device to return a non-CRS completion.  Read the
-	 * Command register instead of Vendor ID so we don't have to
-	 * contend with the CRS SV value.
+	 * Wait for the device to return a non-CRS completion.  On devices
+	 * that support PM control and on waits that aren't part of system
+	 * resume read the PM control register to ensure the device has
+	 * transitioned to D0.  On devices that don't support PM control,
+	 * or during system resume read the command register to instead of
+	 * Vendor ID so we don't have to contend with the CRS SV value.
 	 */
 	for (;;) {
-		u32 id;
 
 		if (pci_dev_is_disconnected(dev)) {
 			pci_dbg(dev, "disconnected; not waiting\n");
 			return -ENOTTY;
 		}
 
-		pci_read_config_dword(dev, PCI_COMMAND, &id);
-		if (!PCI_POSSIBLE_ERROR(id))
-			break;
+		if (dev->pm_cap && strcmp(reset_type, "resume") != 0) {
+			u16 pmcsr;
+
+			pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
+			if (!PCI_POSSIBLE_ERROR(pmcsr) &&
+			    (pmcsr & PCI_PM_CTRL_STATE_MASK) == PCI_D0)
+				break;
+		} else {
+			u32 id;
+
+			pci_read_config_dword(dev, PCI_COMMAND, &id);
+			if (!PCI_POSSIBLE_ERROR(id))
+				break;
+		}
 
 		if (delay > timeout) {
 			pci_warn(dev, "not ready %dms after %s; giving up\n",
-- 
2.43.0