PCI: Protect Link Control 2 Register with RMW locking

The PCIe Bandwidth Controller performs RMW accesses the Link Control 2
Register which can occur concurrently to other sources of Link Control 2
Register writes. Therefore, add Link Control 2 Register among the PCI
Express Capability Registers that need RMW locking.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Lukas Wunner <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>

Author: ij-intel

Documentation/PCI/pciebus-howto.rst

@@ -221,6 +221,7 @@ a selected set of PCI Express Capability Registers:
 
 * Link Control Register
 * Root Control Register
+* Link Control 2 Register
 
 Any change to those registers should be performed using RMW accessors to
 avoid problems due to concurrent updates. For the up-to-date list of

include/linux/pci.h

@@ -1274,6 +1274,7 @@ static inline int pcie_capability_clear_and_set_word(struct pci_dev *dev,
 {
 	switch (pos) {
 	case PCI_EXP_LNKCTL:
+	case PCI_EXP_LNKCTL2:
 	case PCI_EXP_RTCTL:
 		return pcie_capability_clear_and_set_word_locked(dev, pos,
 								 clear, set);