[v2 PATCH] PCI: Do not use bus number zero from EA capability

[sundeep.lkml@gmail.com]

From: Subbaraya Sundeep <sbhatta@marvell.com>

As per the spec, "Enhanced Allocation (EA) for Memory
and I/O Resources" ECN, approved 23 October 2014,
sec 6.9.1.2, fixed bus numbers of a bridge must be zero
when no function that uses EA is located behind it.
Hence assign bus numbers normally instead of assigning
zeroes from EA capability. Failing to do this and using
zeroes from EA would make the bridges non-functional.

Fixes: '2dbce5901179 ("PCI: Assign bus numbers present in
EA capability for bridges")'
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Cc: stable@vger.kernel.org	# v5.2+
---
 drivers/pci/probe.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 3d5271a..116b276 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1090,27 +1090,28 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
  * @sub: updated with subordinate bus number from EA
  *
  * If @dev is a bridge with EA capability, update @sec and @sub with
- * fixed bus numbers from the capability and return true.  Otherwise,
- * return false.
+ * fixed bus numbers from the capability. Otherwise @sec and @sub
+ * will be zeroed.
  */
-static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
+static void pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
 {
 	int ea, offset;
 	u32 dw;
 
+	*sec = *sub = 0;
+
 	if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
-		return false;
+		return;
 
 	/* find PCI EA capability in list */
 	ea = pci_find_capability(dev, PCI_CAP_ID_EA);
 	if (!ea)
-		return false;
+		return;
 
 	offset = ea + PCI_EA_FIRST_ENT;
 	pci_read_config_dword(dev, offset, &dw);
 	*sec =  dw & PCI_EA_SEC_BUS_MASK;
 	*sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
-	return true;
 }
 
 /*
@@ -1146,7 +1147,6 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 	u16 bctl;
 	u8 primary, secondary, subordinate;
 	int broken = 0;
-	bool fixed_buses;
 	u8 fixed_sec, fixed_sub;
 	int next_busnr;
 
@@ -1249,11 +1249,12 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 		pci_write_config_word(dev, PCI_STATUS, 0xffff);
 
 		/* Read bus numbers from EA Capability (if present) */
-		fixed_buses = pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
-		if (fixed_buses)
+		pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
+
+		next_busnr = max + 1;
+		/* Use secondary bus number in EA */
+		if (fixed_sec)
 			next_busnr = fixed_sec;
-		else
-			next_busnr = max + 1;
 
 		/*
 		 * Prevent assigning a bus number that already exists.
@@ -1331,7 +1332,7 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
 		 * If fixed subordinate bus number exists from EA
 		 * capability then use it.
 		 */
-		if (fixed_buses)
+		if (fixed_sub)
 			max = fixed_sub;
 		pci_bus_update_busn_res_end(child, max);
 		pci_write_config_byte(dev, PCI_SUBORDINATE_BUS, max);
-- 
2.7.4