PCI/LINK: Add Kconfig option (default off) [Linux 5.1]

PCI/LINK: Add Kconfig option (default off) [Linux 5.1]

This Linux kernel change "PCI/LINK: Add Kconfig option (default off)" is included in the Linux 5.1 release. This change is authored by Keith Busch <keith.busch [at] intel.com> on Wed May 1 08:29:42 2019 -0600. The commit for this change in Linux stable tree is 2078e1e (patch).

PCI/LINK: Add Kconfig option (default off)

e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth
notification") added dmesg logging whenever a link changes speed or width
to a state that is considered degraded.  Unfortunately, it cannot
differentiate signal integrity-related link changes from those
intentionally initiated by an endpoint driver, including drivers that may
live in userspace or VMs when making use of vfio-pci.  Some GPU drivers
actively manage the link state to save power, which generates a stream of
messages like this:

  vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth, limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5 GT/s x16 link)

Since we can't distinguish the intentional changes from the signal
integrity issues, leave the reporting turned off by default.  Add a Kconfig
option to turn it on if desired.

Fixes: e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth notification")
Link: https://lore.kernel.org/linux-pci/20190501142942[email protected]
Signed-off-by: Keith Busch <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>

There are 14 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/pci/pcie/Kconfig   | 8 ++++++++
 drivers/pci/pcie/Makefile  | 2 +-
 drivers/pci/pcie/portdrv.h | 4 ++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/Kconfig b/drivers/pci/pcie/Kconfig
index 5cbdbca..362eb8c 100644
--- a/drivers/pci/pcie/Kconfig
+++ b/drivers/pci/pcie/Kconfig
@@ -142,3 +142,11 @@ config PCIE_PTM

      This is only useful if you have devices that support PTM, but it
      is safe to enable even if you don't.
+
+config PCIE_BW
+   bool "PCI Express Bandwidth Change Notification"
+   depends on PCIEPORTBUS
+   help
+     This enables PCI Express Bandwidth Change Notification.  If
+     you know link width or rate changes occur only to correct
+     unreliable links, you may answer Y.
diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
index f1d7bc1..efb9d2e 100644
--- a/drivers/pci/pcie/Makefile
+++ b/drivers/pci/pcie/Makefile
@@ -3,7 +3,6 @@
 # Makefile for PCI Express features and port driver

 pcieportdrv-y          := portdrv_core.o portdrv_pci.o err.o
-pcieportdrv-y          += bw_notification.o

 obj-$(CONFIG_PCIEPORTBUS)  += pcieportdrv.o

@@ -13,3 +12,4 @@ obj-$(CONFIG_PCIEAER_INJECT)  += aer_inject.o
 obj-$(CONFIG_PCIE_PME)     += pme.o
 obj-$(CONFIG_PCIE_DPC)     += dpc.o
 obj-$(CONFIG_PCIE_PTM)     += ptm.o
+obj-$(CONFIG_PCIE_BW)      += bw_notification.o
diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h
index 1d50dc5..944827a 100644
--- a/drivers/pci/pcie/portdrv.h
+++ b/drivers/pci/pcie/portdrv.h
@@ -49,7 +49,11 @@
 static inline int pcie_dpc_init(void) { return 0; }
 #endif

+#ifdef CONFIG_PCIE_BW
 int pcie_bandwidth_notification_init(void);
+#else
+static inline int pcie_bandwidth_notification_init(void) { return 0; }
+#endif

 /* Port Type */
 #define PCIE_ANY_PORT          (~0)

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