6.6-stable review patch. If anyone has any objections, please let me know.
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From: Maciej W. Rozycki macro@orcam.me.uk
commit 8037ac08c2bbb3186f83a5a924f52d1048dbaec5 upstream.
The LBMS bit, where implemented, is set by hardware either in response to the completion of retraining caused by writing 1 to the Retrain Link bit or whenever hardware has changed the link speed or width in attempt to correct unreliable link operation. It is never cleared by hardware other than by software writing 1 to the bit position in the Link Status register and we never do such a write.
We currently have two places, namely apply_bad_link_workaround() and pcie_failed_link_retrain() in drivers/pci/controller/dwc/pcie-tegra194.c and drivers/pci/quirks.c respectively where we check the state of the LBMS bit and neither is interested in the state of the bit resulting from the completion of retraining, both check for a link fault.
And in particular pcie_failed_link_retrain() causes issues consequently, by trying to retrain a link where there's no downstream device anymore and the state of 1 in the LBMS bit has been retained from when there was a device downstream that has since been removed.
Clear the LBMS bit then at the conclusion of pcie_retrain_link(), so that we have a single place that controls it and that our code can track link speed or width changes resulting from unreliable link operation.
Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures") Link: https://lore.kernel.org/r/alpine.DEB.2.21.2408091133140.61955@angie.orcam.me... Reported-by: Matthew W Carlis mattc@purestorage.com Link: https://lore.kernel.org/r/20240806000659.30859-1-mattc@purestorage.com/ Link: https://lore.kernel.org/r/20240722193407.23255-1-mattc@purestorage.com/ Signed-off-by: Maciej W. Rozycki macro@orcam.me.uk Signed-off-by: Bjorn Helgaas bhelgaas@google.com Signed-off-by: Krzysztof Wilczyński kwilczynski@kernel.org Cc: stable@vger.kernel.org # v6.5+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/pci/pci.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -5017,7 +5017,15 @@ int pcie_retrain_link(struct pci_dev *pd pcie_capability_clear_word(pdev, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_RL); }
- return pcie_wait_for_link_status(pdev, use_lt, !use_lt); + rc = pcie_wait_for_link_status(pdev, use_lt, !use_lt); + + /* + * Clear LBMS after a manual retrain so that the bit can be used + * to track link speed or width changes made by hardware itself + * in attempt to correct unreliable link operation. + */ + pcie_capability_write_word(pdev, PCI_EXP_LNKSTA, PCI_EXP_LNKSTA_LBMS); + return rc; }
/**