[PATCH v2 1/1] PCI: pcie_bus_config can be set at build time

From: Jim Quinlan
Date: Wed Sep 16 2020 - 17:08:36 EST

The Kconfig is modified so that the pcie_bus_config setting can be done at
build time in the same manner as the CONFIG_PCIEASPM_XXXX choice. The
pci_bus_config setting may still be overridden by the bootline param.

Signed-off-by: Jim Quinlan <james.quinlan@xxxxxxxxxxxx>
drivers/pci/Kconfig | 56 +++++++++++++++++++++++++++++++++++++++++++++
drivers/pci/pci.c | 12 ++++++++++
2 files changed, 68 insertions(+)

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 4bef5c2bae9f..15ce948858fb 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -187,6 +187,62 @@ 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.

+ prompt "PCIE default bus config setting"
+ depends on PCI
+ help
+ One of the following choices will set the pci_bus_config at
+ compile time. The choices offered are the same as those offered
+ for the bootline 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 is still be overridden by the
+ above bootline parameters, if present. If unsure, chose PCIE_BUS_DEFAULT.
+ bool "Tune Off"
+ depends on PCI
+ help
+ Use the BIOS defaults; doesn't touch MPS at all. This is the same
+ as booting with 'pci=pcie_bus_tune_off'.
+ bool "Default"
+ depends on PCI
+ help
+ Default choice; ensures that the MPS matches upstream bridge.
+ 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'.
+ bool "Performance"
+ depends on PCI
+ help
+ Use MPS and MRRS for best performance. This setting ensures
+ 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 and eventually the PHB. This is the same as
+ booting with 'pci=pcie_bus_perf'.
+ 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. Simply making the system
+ wide MPS be set to the smallest possible value (128B) solves
+ this issue. This is the same as booting with 'pci=pcie_bus_peer2peer'.
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 e39c5499770f..dfb52ed4a931 100644
--- 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;
unsigned long pci_hotplug_bus_size = DEFAULT_HOTPLUG_BUS_SIZE;

+/* PCIE bus config, can be overridden by bootline param */
+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;
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PERFORMANCE;
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PEER2PEER;
enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;

* The default CLS is used if arch didn't set CLS explicitly and not

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