[pci] pci/mrst: Detect loops when reading fixed BAR cap.

[Ben Greear <greearb@candelatech.com>]

The mrst logic introduced in 2.6.33-rc8 in commit
a712ffbc199849364c46e9112b93b66de08e2c26 causes boot
to hang on at least this platform:

Intel E5405 CPU
System Information
	Manufacturer: Supermicro
	Product Name: X7DBU

The cause of the hang is that pci_cap points to itself
as the next capability, putting the fixed_bar_cap into
an endless loop.

This patch detects the loop, prints a warning, and
continues on with useful work.  This strategy was
suggested by Robert Hancock <hancockrwd@gmail.com>

This should be a candidate for 2.6.34.y as well.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
:100644 100644 1cdc02c... 9535ba9... M	arch/x86/pci/mrst.c
 arch/x86/pci/mrst.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/arch/x86/pci/mrst.c b/arch/x86/pci/mrst.c
index 1cdc02c..9535ba9 100644
--- a/arch/x86/pci/mrst.c
+++ b/arch/x86/pci/mrst.c
@@ -76,6 +76,17 @@ static int fixed_bar_cap(struct pci_bus *bus, unsigned int devfn)
 				return pos;
 		}
 
+		if ((pcie_cap >> 20) == 0)
+			break;
+		
+		if ((pcie_cap >> 20) <= pos) {
+			printk(KERN_WARNING "WARNING: mrst:  detected loop"
+			       " when searching for fixed BAR cap, previous"
+			       " position: 0x%x new position: 0x%x"
+			       " bus-number: %i  devfn: %i\n",
+			       pos, pcie_cap >> 20, bus->number, devfn);
+			break;
+		}
 		pos = pcie_cap >> 20;
 	}
 
-- 
1.6.2.5