linux-kernel - [PATCH] PCI: Do not use bus number zero from EA capability

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Date:   Mon,  2 Sep 2019 21:00:03 +0530
From:   sundeep.lkml@...il.com
To:     helgaas@...nel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, sean.stalley@...el.com,
        bhelgaas@...gle.com
Cc:     sgoutham@...vell.com, Subbaraya Sundeep <sbhatta@...vell.com>
Subject: [PATCH] PCI: Do not use bus number zero from EA capability

From: Subbaraya Sundeep <sbhatta@...vell.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 can be zero
when no function that uses EA is located behind it.
Hence assign bus numbers sequentially when fixed bus
numbers are zero.

Fixes: 2dbce590117981196fe355efc0569bc6f949ae9b

Signed-off-by: Subbaraya Sundeep <sbhatta@...vell.com>
---
 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 a3c7338..c06ca4c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1095,27 +1095,28 @@ 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;
 }
 
 /*
@@ -1151,7 +1152,6 @@ 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;
 
@@ -1254,11 +1254,12 @@ 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.
@@ -1336,7 +1337,7 @@ 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