From: Ilpo Järvinen ilpo.jarvinen@linux.intel.com
[ Upstream commit e7e39756363ad5bd83ddeae1063193d0f13870fd ]
PCIe r6.0.1, sec 7.5.3.7, recommends setting the link control parameters, then waiting for the Link Training bit to be clear before setting the Retrain Link bit.
This avoids a race where the LTSSM may not use the updated parameters if it is already in the midst of link training because of other normal link activity.
Wait for the Link Training bit to be clear before toggling the Retrain Link bit to ensure that the LTSSM uses the updated link control parameters.
[bhelgaas: commit log, return 0 (success)/-ETIMEDOUT instead of bool for both pcie_wait_for_retrain() and the existing pcie_retrain_link()] Suggested-by: Lukas Wunner lukas@wunner.de Fixes: 7d715a6c1ae5 ("PCI: add PCI Express ASPM support") Link: https://lore.kernel.org/r/20230502083923.34562-1-ilpo.jarvinen@linux.intel.c... Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Signed-off-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Lukas Wunner lukas@wunner.de Cc: stable@vger.kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/pci/pcie/aspm.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c index 749a367bde2df..55270180ae081 100644 --- a/drivers/pci/pcie/aspm.c +++ b/drivers/pci/pcie/aspm.c @@ -220,8 +220,19 @@ static int pcie_wait_for_retrain(struct pci_dev *pdev) static int pcie_retrain_link(struct pcie_link_state *link) { struct pci_dev *parent = link->pdev; + int rc; u16 reg16;
+ /* + * Ensure the updated LNKCTL parameters are used during link + * training by checking that there is no ongoing link training to + * avoid LTSSM race as recommended in Implementation Note at the + * end of PCIe r6.0.1 sec 7.5.3.7. + */ + rc = pcie_wait_for_retrain(parent); + if (rc) + return rc; + pcie_capability_read_word(parent, PCI_EXP_LNKCTL, ®16); reg16 |= PCI_EXP_LNKCTL_RL; pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);