diff options
| -rw-r--r-- | drivers/pci/probe.c | 32 |
1 files changed, 16 insertions, 16 deletions
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 0591b087a6c3..94b1d227ddcd 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -1491,23 +1491,23 @@ static int pcie_find_smpss(struct pci_dev *dev, void *data) if (!pci_is_pcie(dev)) return 0; - /* For PCIE hotplug enabled slots not connected directly to a - * PCI-E root port, there can be problems when hotplugging - * devices. This is due to the possibility of hotplugging a - * device into the fabric with a smaller MPS that the devices - * currently running have configured. Modifying the MPS on the - * running devices could cause a fatal bus error due to an - * incoming frame being larger than the newly configured MPS. - * To work around this, the MPS for the entire fabric must be - * set to the minimum size. Any devices hotplugged into this - * fabric will have the minimum MPS set. If the PCI hotplug - * slot is directly connected to the root port and there are not - * other devices on the fabric (which seems to be the most - * common case), then this is not an issue and MPS discovery - * will occur as normal. + /* + * We don't have a way to change MPS settings on devices that have + * drivers attached. A hot-added device might support only the minimum + * MPS setting (MPS=128). Therefore, if the fabric contains a bridge + * where devices may be hot-added, we limit the fabric MPS to 128 so + * hot-added devices will work correctly. + * + * However, if we hot-add a device to a slot directly below a Root + * Port, it's impossible for there to be other existing devices below + * the port. We don't limit the MPS in this case because we can + * reconfigure MPS on both the Root Port and the hot-added device, + * and there are no other devices involved. + * + * Note that this PCIE_BUS_SAFE path assumes no peer-to-peer DMA. */ - if (dev->is_hotplug_bridge && (!list_is_singular(&dev->bus->devices) || - pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT)) + if (dev->is_hotplug_bridge && + pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) *smpss = 0; if (*smpss > dev->pcie_mpss) |