PCI: Add Kconfig options for MPS/MRRS strategy

Add Kconfig options for changing the default pcie_bus_config, i.e., the
strategy for configuration MPS and MRRS, in the same manner as the
CONFIG_PCIEASPM_XXXX choice.  The pci_bus_config setting may still be
overridden by kernel command-line parameters, e.g.,
"pci=pcie_bus_tune_off".

[bhelgaas: depend on EXPERT, tweak help texts]
Link: https://lore.kernel.org/r/20200928194651.5393-2-james.quinlan@broadcom.com
Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 4bef5c2bae9f587e5739b3cb8b57a4fc270b7681..d323b25ae27e4bc6d0bea410e84b11e2b34c59f7 100644 (file)
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -187,6 +187,68 @@ config PCI_HYPERV
          The PCI device frontend driver allows the kernel to import arbitrary
          PCI devices from a PCI backend to support PCI driver domains.
 
+choice
+       prompt "PCI Express hierarchy optimization setting"
+       default PCIE_BUS_DEFAULT
+       depends on PCI && EXPERT
+       help
+         MPS (Max Payload Size) and MRRS (Max Read Request Size) are PCIe
+         device parameters that affect performance and the ability to
+         support hotplug and peer-to-peer DMA.
+
+         The following choices set the MPS and MRRS optimization strategy
+         at compile-time.  The choices are the same as those offered for
+         the kernel command-line parameter 'pci', i.e.,
+         'pci=pcie_bus_tune_off', 'pci=pcie_bus_safe',
+         'pci=pcie_bus_perf', and 'pci=pcie_bus_peer2peer'.
+
+         This is a compile-time setting and can be overridden by the above
+         command-line parameters.  If unsure, choose PCIE_BUS_DEFAULT.
+
+config PCIE_BUS_TUNE_OFF
+       bool "Tune Off"
+       depends on PCI
+       help
+         Use the BIOS defaults; don't touch MPS at all.  This is the same
+         as booting with 'pci=pcie_bus_tune_off'.
+
+config PCIE_BUS_DEFAULT
+       bool "Default"
+       depends on PCI
+       help
+         Default choice; ensure that the MPS matches upstream bridge.
+
+config PCIE_BUS_SAFE
+       bool "Safe"
+       depends on PCI
+       help
+         Use largest MPS that boot-time devices support.  If you have a
+         closed system with no possibility of adding new devices, this
+         will use the largest MPS that's supported by all devices.  This
+         is the same as booting with 'pci=pcie_bus_safe'.
+
+config PCIE_BUS_PERFORMANCE
+       bool "Performance"
+       depends on PCI
+       help
+         Use MPS and MRRS for best performance.  Ensure that a given
+         device's MPS is no larger than its parent MPS, which allows us to
+         keep all switches/bridges to the max MPS supported by their
+         parent.  This is the same as booting with 'pci=pcie_bus_perf'.
+
+config PCIE_BUS_PEER2PEER
+       bool "Peer2peer"
+       depends on PCI
+       help
+         Set MPS = 128 for all devices.  MPS configuration effected by the
+         other options could cause the MPS on one root port to be
+         different than that of the MPS on another, which may cause
+         hot-added devices or peer-to-peer DMA to fail.  Set MPS to the
+         smallest possible value (128B) system-wide to avoid these issues.
+         This is the same as booting with 'pci=pcie_bus_peer2peer'.
+
+endchoice
+
 source "drivers/pci/hotplug/Kconfig"
 source "drivers/pci/controller/Kconfig"
 source "drivers/pci/endpoint/Kconfig"

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a458c46d7e39d13c722d733cebc1c80d7f4b3ae1..09c5cbd5a52ccd88a604d3aa592d8618dc00b152 100644 (file)
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -101,7 +101,19 @@ unsigned long pci_hotplug_mmio_pref_size = DEFAULT_HOTPLUG_MMIO_PREF_SIZE;
 #define DEFAULT_HOTPLUG_BUS_SIZE       1
 unsigned long pci_hotplug_bus_size = DEFAULT_HOTPLUG_BUS_SIZE;
 
+
+/* PCIe MPS/MRRS strategy; can be overridden by kernel command-line param */
+#ifdef CONFIG_PCIE_BUS_TUNE_OFF
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_TUNE_OFF;
+#elif defined CONFIG_PCIE_BUS_SAFE
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_SAFE;
+#elif defined CONFIG_PCIE_BUS_PERFORMANCE
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PERFORMANCE;
+#elif defined CONFIG_PCIE_BUS_PEER2PEER
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PEER2PEER;
+#else
 enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;
+#endif
 
 /*
  * The default CLS is used if arch didn't set CLS explicitly and not