This commit adds the field 'subordinate' to struct pci_bus. Normally,
the subordinate is automatically calculated while scanning children of
the bus and counting their downstream buses.
This heuristic fails for hot-added bridges. A hot-added bridge will
need to increase its subordinate if additional bridges are hot-added
underneath it. Without the 'subordinate' field, newly added bridges
will not have a valid secondary number, without reshuffling all
existing devices.
By storing the bus's intended subordinate number, the scanning
algorithm can skip over reserved numbers while enumerating devices. A
subordinate value of 0 means to use the existing enumeration
algorithm. An upcoming commit will set that subordinate field to a
non-zero value.
Signed-off-by: Jason Tang <jason.tang2@xxxxxxx>
---
drivers/pci/probe.c | 23 ++++++++++++++++++++---
include/linux/pci.h | 1 +
2 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index c905db3..58ae892 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -863,8 +863,17 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
if (!child)
goto out;
pci_bus_insert_busn_res(child, child->number, 0xff);
+ /* child's subordinate bus will be calculated
+ during pass 2 */
}
- max++;
+
+ /* if the child bus has a subordinate value set, then
+ use that bus's subordinate+1 as the next probed bus
+ number */
+ if (max < child->subordinate)
+ max = child->subordinate + 1;
+ else
+ max++;
buses = (buses & 0xff000000)
| ((unsigned int)(child->primary) << 0)
| ((unsigned int)(child->busn_res.start) << 8)
@@ -921,8 +930,10 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
/*
* Set the subordinate bus number to its real value.
*/
- pci_bus_update_busn_res_end(child, max);
- pci_write_config_byte(dev, PCI_SUBORDINATE_BUS, max);
+ child->subordinate = max;
+ pci_bus_update_busn_res_end(child, child->subordinate);
+ pci_write_config_byte(dev, PCI_SUBORDINATE_BUS,
+ child->subordinate);
}
sprintf(child->name,
@@ -1896,6 +1907,12 @@ unsigned int pci_scan_child_bus(struct pci_bus *bus)
}
/*
+ * Adjust max if this bus has a set subordinate number
+ */
+ if (max < bus->subordinate)
+ max = bus->subordinate;
+
+ /*
* We've scanned the bus and so we know all about what's on
* the other side of any bridges that may be on this bus plus
* any devices.
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 8a0321a..384106c 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -458,6 +458,7 @@ struct pci_bus {
unsigned char number; /* bus number */
unsigned char primary; /* number of primary bridge */
+ unsigned char subordinate; /* subordinate number on secondary bridge */
unsigned char max_bus_speed; /* enum pci_bus_speed */
unsigned char cur_bus_speed; /* enum pci_bus_speed */
#ifdef CONFIG_PCI_DOMAINS_GENERIC
--
1.8.3.1
--
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