[PATCH v5] powerpc/pci: Assign fixed PHB number based on device-tree properties

["Guilherme G. Piccoli" <gpiccoli@linux.vnet.ibm.com>]

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 PCI device hotplug.

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.

Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/pci-common.c | 66 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 3 deletions(-)

v5:
  * Improved comments.

  * Changed the the Fixed PHB Numbering to set the PHB number bit
  on the bitmap anyway, avoiding issues when system has virtual PHBs.

  * Changed the device-tree check order - now, firstly we check for
  "ibm,opal-phbid" and if it's not available, we try the pSeries case.

v4:
  * Minor change (if/else nesting rearranged).

v3:
  * Made the bitmap static.

  * Rearranged if/else statements of Fixed PHB checking.

  * Improved bitmap checkings, by removing loop and using instead the
  find_first_zero_bit() function.

  * Removed the single-statement function release_phb_number() by
  adding its logic directly into pcibios_free_controller().

  *Added check for bitmap size before clearing bit, avoiding memory
  corruption.

v2:
  * Added the Fixed PHB Numbering mechanism based on device-tree
  properties.

  * Changed list approach to bitmap on the Dynamic PHB Numbering
  mechanism.

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index 0f7a60f..ad423c1 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -41,11 +41,17 @@
 #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	8192
+
+/* 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 +70,55 @@ struct dma_map_ops *get_pci_dma_ops(void)
 }
 EXPORT_SYMBOL(get_pci_dma_ops);
 
+/* get_phb_number() function should run under locking
+ * protection, specifically hose_spinlock.
+ */
+static int get_phb_number(struct device_node *dn)
+{
+	const __be64 *prop64;
+	const __be32 *regs;
+	int phb_id = 0;
+
+	/* 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.
+	 */
+	prop64 = of_get_property(dn, "ibm,opal-phbid", NULL);
+	if (prop64) {
+		phb_id = (int)(be64_to_cpup(prop64) & 0xFFFF);
+
+	} else if (machine_is(pseries)) {
+		regs = of_get_property(dn, "reg", NULL);
+		if (regs)
+			phb_id = (int)(be32_to_cpu(regs[1]) & 0xFFFF);
+	} else {
+		goto dynamic_phb_numbering;
+	}
+
+	/* If we have a huge PHB number obtained from device-tree, no need
+	 * to worry with the bitmap. Otherwise, we need to be sure we're
+	 * not trying to use the same PHB number twice.
+	 */
+	if (phb_id < MAX_PHBS) {
+		if (test_bit(phb_id, phb_bitmap))
+			goto dynamic_phb_numbering;
+		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.
+	 */
+dynamic_phb_numbering:
+
+	phb_id = find_first_zero_bit(phb_bitmap, MAX_PHBS);
+	BUG_ON(phb_id >= MAX_PHBS); /* Reached maximum number of 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 +127,7 @@ 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 +149,11 @@ 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