[PATCH v7] powerpc/pci: Assign fixed PHB number based on device-tree properties

[Guilherme G. Piccoli]

The domain/PHB field of PCI addresses has its value obtained from a
global variable, incremented each time a new domain (represented by
struct pci_controller) is added on the system. The domain addition
process happens during boot or due to PHB hotplug add.

As recent kernels are using predictable naming for network interfaces,
the network stack is more tied to PCI naming. This can be a problem in
hotplug scenarios, because PCI addresses will change if devices are
removed and then re-added. This situation seems unusual, but it can
happen if a user wants to replace a NIC without rebooting the machine,
for example.

This patch changes the way PCI domain values are generated: now, we use
device-tree properties to assign fixed PHB numbers to PCI addresses
when available (meaning pSeries and PowerNV cases). We also use a bitmap
to allow dynamic PHB numbering when device-tree properties are not
used. This bitmap keeps track of used PHB numbers and if a PHB is
released (by hotplug operations for example), it allows the reuse of
this PHB number, avoiding PCI address to change in case of device remove
and re-add soon after. No functional changes were introduced.

Signed-off-by: Guilherme G. Piccoli <gpiccoli at linux.vnet.ibm.com>
Reviewed-by: Gavin Shan <gwshan at linux.vnet.ibm.com>
Reviewed-by: Ian Munsie <imunsie at au1.ibm.com>
---
v7:
    * Removed the goto as per Michael's suggestion;

    * Changed of_property_read_u32_array() to of_property_read_u32_index(),
as per Gavin's suggestion. This way, we end up using buid_low as the index
of PHB in pSeries, which is expected but was not being achieved in v6,
as per my mistake.

    * Didn't remove machine check for pSeries on "reg" property lookup.
It's worthy to keep it, since almost every platform (if not all of them)
contain the "reg" property on PHB node in device-tree, but only in
pSeries we're 100% sure it can be used as the PHB unique identifier.
Since the patch has a dynamic PHB numbering mechanism, the other platforms
won't have trouble with it.

 arch/powerpc/kernel/pci-common.c | 53 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index 0f7a60f..c87545b 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -41,11 +41,18 @@
 #include <asm/ppc-pci.h>
 #include <asm/eeh.h>
 
+/* hose_spinlock protects accesses to the the phb_bitmap. */
 static DEFINE_SPINLOCK(hose_spinlock);
 LIST_HEAD(hose_list);
 
-/* XXX kill that some day ... */
-static int global_phb_number;		/* Global phb counter */
+/* For dynamic PHB numbering on get_phb_number(): max number of PHBs. */
+#define MAX_PHBS 0x10000
+
+/*
+ * For dynamic PHB numbering: used/free PHBs tracking bitmap.
+ * Accesses to this bitmap should be protected by hose_spinlock.
+ */
+static DECLARE_BITMAP(phb_bitmap, MAX_PHBS);
 
 /* ISA Memory physical address */
 resource_size_t isa_mem_base;
@@ -64,6 +71,41 @@ struct dma_map_ops *get_pci_dma_ops(void)
 }
 EXPORT_SYMBOL(get_pci_dma_ops);
 
+/*
+ * This function should run under locking protection, specifically
+ * hose_spinlock.
+ */
+static int get_phb_number(struct device_node *dn)
+{
+	u64 prop;
+	int ret, phb_id = -1;
+
+	/*
+	 * Try fixed PHB numbering first, by checking archs and reading
+	 * the respective device-tree properties. Firstly, try PowerNV by
+	 * reading "ibm,opal-phbid", only present in OPAL environment.
+	 */
+	ret = of_property_read_u64(dn, "ibm,opal-phbid", &prop);
+	if (ret && machine_is(pseries))
+		ret = of_property_read_u32_index(dn, "reg", 1, (u32 *)&prop);
+	if (!ret)
+		phb_id = (int)(prop & (MAX_PHBS - 1));
+
+	/* We need to be sure to not use the same PHB number twice. */
+	if ((phb_id >= 0) && !test_and_set_bit(phb_id, phb_bitmap))
+		return phb_id;
+
+	/*
+	 * If not pSeries nor PowerNV, or if fixed PHB numbering tried to add
+	 * the same PHB number twice, then fallback to dynamic PHB numbering.
+	 */
+	phb_id = find_first_zero_bit(phb_bitmap, MAX_PHBS);
+	BUG_ON(phb_id >= MAX_PHBS);
+	set_bit(phb_id, phb_bitmap);
+
+	return phb_id;
+}
+
 struct pci_controller *pcibios_alloc_controller(struct device_node *dev)
 {
 	struct pci_controller *phb;
@@ -72,7 +114,7 @@ struct pci_controller *pcibios_alloc_controller(struct device_node *dev)
 	if (phb == NULL)
 		return NULL;
 	spin_lock(&hose_spinlock);
-	phb->global_number = global_phb_number++;
+	phb->global_number = get_phb_number(dev);
 	list_add_tail(&phb->list_node, &hose_list);
 	spin_unlock(&hose_spinlock);
 	phb->dn = dev;
@@ -94,6 +136,11 @@ EXPORT_SYMBOL_GPL(pcibios_alloc_controller);
 void pcibios_free_controller(struct pci_controller *phb)
 {
 	spin_lock(&hose_spinlock);
+
+	/* Clear bit of phb_bitmap to allow reuse of this PHB number. */
+	if (phb->global_number < MAX_PHBS)
+		clear_bit(phb->global_number, phb_bitmap);
+
 	list_del(&phb->list_node);
 	spin_unlock(&hose_spinlock);
 
-- 
2.1.0