Patch "PCI/ASPM: Avoid link retraining race" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    PCI/ASPM: Avoid link retraining race

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pci-aspm-avoid-link-retraining-race.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit acdac95be473026b932ce7398769cc8dac26b582
Author: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Date:   Tue May 2 11:39:23 2023 +0300

    PCI/ASPM: Avoid link retraining race
    
    [ 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@xxxxxxxxx>
    Fixes: 7d715a6c1ae5 ("PCI: add PCI Express ASPM support")
    Link: https://lore.kernel.org/r/20230502083923.34562-1-ilpo.jarvinen@xxxxxxxxxxxxxxx
    Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
    Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
    Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 7b1fb6cb16fba..eec62f7377f48 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -223,8 +223,19 @@ 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, &reg16);
 	reg16 |= PCI_EXP_LNKCTL_RL;
 	pcie_capability_write_word(parent, PCI_EXP_LNKCTL, reg16);