| Message ID | 1481070027-9096-1-git-send-email-jon.mason@broadcom.com |
|---|---|
| State | Changes Requested |
| Headers | show |
On Tue, Dec 06, 2016 at 07:20:27PM -0500, Jon Mason wrote: > Not all systems have a BIOS or firmware to preconfigure the PCIE MPS > prior to Linux booting. Without any firmware to pre-setup the MPS, the > PCIE_BUS_DEFAULT will simply set everything to 0 (128b). This behavior > causes these systems to have non-optimal MPS values. To get around this > issue, change the default value of pcie_bus_config to be PCIE_BUS_SAFE. > This configures all systems to use better values for the MPS, at the > expense of any potential HW errata that might not like being changed. Wouldn't it be better to provide the kernel parameter to override the default on such platforms? The PCIE_BUS_SAFE sets the MPS to the lowest common denominator below the root port, which may be less optimal than the default behavior for hot plug. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index ba34907..94d574e 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -88,7 +88,7 @@ unsigned long pci_hotplug_mem_size = DEFAULT_HOTPLUG_MEM_SIZE; #define DEFAULT_HOTPLUG_BUS_SIZE 1 unsigned long pci_hotplug_bus_size = DEFAULT_HOTPLUG_BUS_SIZE; -enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT; +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_SAFE; /* * The default CLS is used if arch didn't set CLS explicitly and not
Not all systems have a BIOS or firmware to preconfigure the PCIE MPS prior to Linux booting. Without any firmware to pre-setup the MPS, the PCIE_BUS_DEFAULT will simply set everything to 0 (128b). This behavior causes these systems to have non-optimal MPS values. To get around this issue, change the default value of pcie_bus_config to be PCIE_BUS_SAFE. This configures all systems to use better values for the MPS, at the expense of any potential HW errata that might not like being changed. Signed-off-by: Jon Mason <jon.mason@broadcom.com> --- drivers/pci/pci.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)