PCI: Wait for up to 1000ms after FLR reset

Some devices take longer than the spec indicates to return from FLR reset,
a notable case of this is Intel integrated graphics (IGD), which can often
take an additional 300ms powering down an attached LCD panel as part of the
FLR.  Allow devices up to 1000ms, testing every 100ms whether the second
dword of config space is read as -1.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -3414,6 +3414,29 @@ int pci_wait_for_pending_transaction(struct pci_dev *dev)
 }
 EXPORT_SYMBOL(pci_wait_for_pending_transaction);
 
+/*
+ * We should only need to wait 100ms after FLR, but some devices take longer.
+ * Wait for up to 1000ms for config space to return something other than -1.
+ * Intel IGD requires this when an LCD panel is attached.  We read the 2nd
+ * dword because VFs don't implement the 1st dword.
+ */
+static void pci_flr_wait(struct pci_dev *dev)
+{
+	int i = 0;
+	u32 id;
+
+	do {
+		msleep(100);
+		pci_read_config_dword(dev, PCI_COMMAND, &id);
+	} while (i++ < 10 && id == ~0);
+
+	if (id == ~0)
+		dev_warn(&dev->dev, "Failed to return from FLR\n");
+	else if (i > 1)
+		dev_info(&dev->dev, "Required additional %dms to return from FLR\n",
+			 (i - 1) * 100);
+}
+
 static int pcie_flr(struct pci_dev *dev, int probe)
 {
 	u32 cap;
@@ -3429,7 +3452,7 @@ static int pcie_flr(struct pci_dev *dev, int probe)
 		dev_err(&dev->dev, "timed out waiting for pending transaction; performing function level reset anyway\n");
 
 	pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_BCR_FLR);
-	msleep(100);
+	pci_flr_wait(dev);
 	return 0;
 }
 
@@ -3459,7 +3482,7 @@ static int pci_af_flr(struct pci_dev *dev, int probe)
 		dev_err(&dev->dev, "timed out waiting for pending transaction; performing AF function level reset anyway\n");
 
 	pci_write_config_byte(dev, pos + PCI_AF_CTRL, PCI_AF_CTRL_FLR);
-	msleep(100);
+	pci_flr_wait(dev);
 	return 0;
 }