[PATCH v4 02/11] PCI: Make link retraining use RMW accessors for changing LNKCTL

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Don't assume that the device is fully under the control of PCI core.
Use RMW capability accessors in link retraining which do proper locking
to avoid losing concurrent updates to the register values.

Fixes: 4ec73791a64b ("PCI: Work around Pericom PCIe-to-PCI bridge Retrain Link erratum")
Fixes: 7d715a6c1ae5 ("PCI: add PCI Express ASPM support")
Suggested-by: Lukas Wunner <lukas@xxxxxxxxx>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

pci/enumeration branch moves the link retraining code into PCI core and
also conflicts with a link retraining fix in pci/aspm. The changelog
(and patch splitting) takes the move into account by not referring to
ASPM while the change itself is not based on pci/enumeration (as per
Bjorn's preference).
 drivers/pci/pci.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 60230da957e0..f7315b13bb82 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4927,7 +4927,6 @@ static int pcie_wait_for_link_status(struct pci_dev *pdev,
 int pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
 	int rc;
-	u16 lnkctl;
 	 * Ensure the updated LNKCTL parameters are used during link
@@ -4939,17 +4938,14 @@ int pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
 	if (rc)
 		return rc;
-	pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &lnkctl);
-	lnkctl |= PCI_EXP_LNKCTL_RL;
-	pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
+	pcie_capability_set_word(pdev, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_RL);
 	if (pdev->clear_retrain_link) {
 		 * Due to an erratum in some devices the Retrain Link bit
 		 * needs to be cleared again manually to allow the link
 		 * training to succeed.
-		lnkctl &= ~PCI_EXP_LNKCTL_RL;
-		pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
+		pcie_capability_clear_word(pdev, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_RL);
 	return pcie_wait_for_link_status(pdev, use_lt, !use_lt);

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