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PCI: Remove MPS/MRRS Kconfig settings (CONFIG_PCIE_BUS_*)

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Revert b0e85c3c85 ("PCI: Add Kconfig options for MPS/MRRS strategy"),
which allowed build-time selection of the "off", "default", "safe",
"performance", or "peer2peer" strategies for MPS and MRRS configuration.
These strategies can be selected at boot-time using the
"pci=pcie_bus_tune_*" kernel parameters.

Per the discussion mentioned below, these Kconfig options were added to
work around a hardware defect in a WiFi device used in a cable modem.  The
defect occurred only when the device was configured with MPS=128, and
Kconfig was a way to avoid that setting.  It was easier for the modem
vendor to use Kconfig and update the kernel image than to change the kernel
parameters.

Neither Kconfig nor kernel parameters are a complete solution because the
broken WiFi device may be used in other systems where it may be configured
with MPS=128 and be susceptible to the defect.

Remove the Kconfig settings to simplify the MPS code.  If we can identify
the WiFi device in question, we may be able to make a generic quirk to
avoid the problem on all system.

This is not a fix and should not be backported to previous kernels.

Link: https://lore.kernel.org/all/CA+-6iNzd0RJO0L021qz8CKrSviSst6QehY-QtJxz_-EVY0Hj0Q@mail.gmail.com
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260326221311.1356180-1-bhelgaas@google.com
This commit is contained in:
Bjorn Helgaas
2026-03-26 17:13:11 -05:00
parent 254f49634e
commit bb115505a9
2 changed files with 0 additions and 67 deletions
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57
drivers/pci/Kconfig
View File

@@ -251,63 +251,6 @@ config PCI_DYNAMIC_OF_NODES
Once this option is selected, the device tree nodes will be generated
for all PCI bridges.
choice
prompt "PCI Express hierarchy optimization setting"
default PCIE_BUS_DEFAULT
depends on 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"
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"
help
Default choice; ensure that the MPS matches upstream bridge.
config PCIE_BUS_SAFE
bool "Safe"
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"
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"
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
config VGA_ARB
bool "VGA Arbitration" if EXPERT
default y

10
drivers/pci/pci.c
View File

@@ -120,17 +120,7 @@ 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