PCI: Abstract LBMS seen check into pcie_lbms_seen()

The Target Speed quirk in pcie_failed_link_retrain() uses the presence of
LBMS bit as one of the triggering conditions, effectively monopolizing the
use of that bit. An upcoming change will introduce a PCIe bandwidth
controller which sets up an interrupt to track LBMS. As LBMS will be
cleared by the interrupt handler, the Target Speed quirk will no longer be
able to observe LBMS directly.

As a preparatory step for the change, extract the LBMS seen check from
pcie_failed_link_retrain() into a new function pcie_lmbs_seen().

Link: https://lore.kernel.org/r/20241018144755.7875-6-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: ij-intel

drivers/pci/quirks.c

@@ -33,6 +33,11 @@
 #include <linux/switchtec.h>
 #include "pci.h"
 
+static bool pcie_lbms_seen(struct pci_dev *dev, u16 lnksta)
+{
+	return lnksta & PCI_EXP_LNKSTA_LBMS;
+}
+
 /*
  * Retrain the link of a downstream PCIe port by hand if necessary.
  *
@@ -96,8 +101,7 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
 
 	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
 	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
-	if ((lnksta & (PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_DLLLA)) ==
-	    PCI_EXP_LNKSTA_LBMS) {
+	if (!(lnksta & PCI_EXP_LNKSTA_DLLLA) && pcie_lbms_seen(dev, lnksta)) {
 		u16 oldlnkctl2 = lnkctl2;
 
 		pci_info(dev, "broken device, retraining non-functional downstream link at 2.5GT/s\n");