Ensure that the max payload size on the root port is the same as the max
payload size on all intermediate bridges and devices. This is required
to work around buggy BIOS revisions found on various whitebox
motherboards which do not configure mps beyond one level below the root
port.
Signed-off-by: Jon Mason <mason@xxxxxxxx>
Signed-off-by: Andrew Gallatin <gallatin@xxxxxxxx>
---
drivers/pci/bus.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 44 insertions(+), 0 deletions(-)
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 69546e9..fc16b67 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -175,6 +175,49 @@ int pci_bus_add_child(struct pci_bus *bus)
return retval;
}
+/*
+ * Ensure that the max payload size on the root port is the same as the max
+ * payload size on all intermediate bridges. This is required to work around
+ * buggy BIOS revisions found on various whitebox motherboards which do not
+ * configure mps beyond one level below the root port.
+ */
+static void pci_mps_workaround(struct pci_dev *child, struct pci_dev *parent)
+{
+ u16 val, pmps, cmps;
+ int cap, rc;
+
+ if (!parent)
+ return;
+
+ cap = pci_find_capability(parent, PCI_CAP_ID_EXP);
+ if (!cap)
+ return;
+
+ rc = pci_read_config_word(parent, cap + PCI_EXP_DEVCTL, &val);
+ if (rc)
+ return;
+
+ pmps = val & PCI_EXP_DEVCTL_PAYLOAD;
+
+ cap = pci_find_capability(child, PCI_CAP_ID_EXP);
+ if (!cap)
+ return;
+
+ rc = pci_read_config_word(child, cap + PCI_EXP_DEVCTL, &val);
+ if (rc)
+ return;
+
+ cmps = val & PCI_EXP_DEVCTL_PAYLOAD;
+
+ if (pmps != cmps) {
+ printk(KERN_WARNING "Child MPS of %d != Parent MPS of %d! "
+ "Most likely caused by bad BIOS. Working around...\n",
+ 128 << (cmps >> 5), 128 << (pmps >> 5));
+ val = (val & ~ PCI_EXP_DEVCTL_PAYLOAD) | pmps;
+ pci_write_config_word(child, cap + PCI_EXP_DEVCTL, val);
+ }
+}
+
/**
* pci_bus_add_devices - insert newly discovered PCI devices
* @bus: bus to check for new devices
@@ -194,6 +237,7 @@ void pci_bus_add_devices(const struct pci_bus *bus)
int retval;
list_for_each_entry(dev, &bus->devices, bus_list) {
+ pci_mps_workaround(dev, dev->bus->self);
/* Skip already-added devices */
if (dev->is_added)
continue;
--
1.7.4.1
--
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