6.11-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 f68dea13405c94381d08f42dbf0416261622bdad upstream.
When `pcie_failed_link_retrain' has failed to retrain the link by hand it leaves the link speed restricted to 2.5GT/s, which will then affect any device that has been plugged in later on, which may not suffer from the problem that caused the speed restriction to have been attempted. Consequently such a downstream device will suffer from an unnecessary communication throughput limitation and therefore performance loss.
Remove the speed restriction then and revert the Link Control 2 register to its original state if link retraining with the speed restriction in place has failed. Retrain the link again afterwards so as to remove any residual state, waiting on LT rather than DLLLA to avoid an excessive delay and ignoring the result as this training is supposed to fail anyway.
Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures") Link: https://lore.kernel.org/linux-pci/alpine.DEB.2.21.2408251412590.30766@angie.... 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 Reviewed-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com Cc: stable@vger.kernel.org # v6.5+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/pci/quirks.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
--- a/drivers/pci/quirks.c +++ b/drivers/pci/quirks.c @@ -66,7 +66,7 @@ * apply this erratum workaround to any downstream ports as long as they * support Link Active reporting and have the Link Control 2 register. * Restrict the speed to 2.5GT/s then with the Target Link Speed field, - * request a retrain and wait 200ms for the data link to go up. + * request a retrain and check the result. * * If this turns out successful and we know by the Vendor:Device ID it is * safe to do so, then lift the restriction, letting the devices negotiate @@ -74,6 +74,10 @@ * firmware may have already arranged and lift it with ports that already * report their data link being up. * + * Otherwise revert the speed to the original setting and request a retrain + * again to remove any residual state, ignoring the result as it's supposed + * to fail anyway. + * * Return TRUE if the link has been successfully retrained, otherwise FALSE. */ bool pcie_failed_link_retrain(struct pci_dev *dev) @@ -92,6 +96,8 @@ bool pcie_failed_link_retrain(struct pci pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta); if ((lnksta & (PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_DLLLA)) == PCI_EXP_LNKSTA_LBMS) { + u16 oldlnkctl2 = lnkctl2; + pci_info(dev, "broken device, retraining non-functional downstream link at 2.5GT/s\n");
lnkctl2 &= ~PCI_EXP_LNKCTL2_TLS; @@ -100,6 +106,9 @@ bool pcie_failed_link_retrain(struct pci
if (pcie_retrain_link(dev, false)) { pci_info(dev, "retraining failed\n"); + pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, + oldlnkctl2); + pcie_retrain_link(dev, true); return false; }