[PATCH 1/1] PCI: Add CONFIG_PCI_NOSPEED_QUIRK to remove pcie_failed_link_retrain

[Matthew W Carlis <mattc@purestorage.com>]

It is desirable to be able to remove pcie_failed_link_retrain for some
systems which are known to have PCIe devices with good LTSSM behavior
or a high degree of compatibility and which may be required to endure
large numbers of hot-plug events or DPC triggers & always arrive at the
maximum link speed. It appears that there is a degree of variability
in DSP/RP behavior in terms of setting the LBMS bit & therefore
difficult to tune pcie_failed_link_retrain with a very high degree
of accuracy in terms of never forcing a device to Gen1 that would
be able to arrive at its maximum speed on its own.

Signed-off-by: Matthew W Carlis <mattc@purestorage.com>
---
 drivers/pci/Kconfig  | 9 +++++++++
 drivers/pci/pci.h    | 8 +++++++-
 drivers/pci/quirks.c | 3 +++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 9c0e4aaf4e8c..8f01808231f7 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -68,6 +68,15 @@ config PCI_QUIRKS
 	  Disable this only if your target machine is unaffected by PCI
 	  quirks.
 
+config PCI_NOSPEED_QUIRK
+	default n
+	bool "Remove forced Gen1 link speed Gen1 quirk" if EXPERT
+	help
+	  This disables a workaround that will guide the PCIe link to
+	  2.5GT/s speed if it thinks the link has failed to train. Enable
+	  this if you think this workaround is forcing the link to 2.5GT/s
+	  when it should not.
+
 config PCI_DEBUG
 	bool "PCI Debugging"
 	depends on DEBUG_KERNEL
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 12215ee72afb..51fddc6419f3 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -785,7 +785,6 @@ void pci_acs_init(struct pci_dev *dev);
 int pci_dev_specific_acs_enabled(struct pci_dev *dev, u16 acs_flags);
 int pci_dev_specific_enable_acs(struct pci_dev *dev);
 int pci_dev_specific_disable_acs_redir(struct pci_dev *dev);
-int pcie_failed_link_retrain(struct pci_dev *dev);
 #else
 static inline int pci_dev_specific_acs_enabled(struct pci_dev *dev,
 					       u16 acs_flags)
@@ -800,11 +799,18 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
 {
 	return -ENOTTY;
 }
+#endif
+
+#ifdef CONFIG_PCI_QUIRKS
+#ifndef CONFIG_PCI_NOSPEED_QUIRK
+int pcie_failed_link_retrain(struct pci_dev *dev);
+#else
 static inline int pcie_failed_link_retrain(struct pci_dev *dev)
 {
 	return -ENOTTY;
 }
 #endif
+#endif
 
 /* PCI error reporting and recovery */
 pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 39bb0c025119..d2d06f9ec983 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -36,6 +36,8 @@
 #include <linux/switchtec.h>
 #include "pci.h"
 
+#ifndef CONFIG_PCI_NOSPEED_QUIRK
+
 static bool pcie_lbms_seen(struct pci_dev *dev, u16 lnksta)
 {
 	if (test_bit(PCI_LINK_LBMS_SEEN, &dev->priv_flags))
@@ -140,6 +142,7 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
 
 	return ret;
 }
+#endif
 
 static ktime_t fixup_debug_start(struct pci_dev *dev,
 				 void (*fn)(struct pci_dev *dev))
-- 
2.46.0