powerpc/pci: Fix endian bug in fixed PHB numbering

The recent commit 63a72284b159 ("powerpc/pci: Assign fixed PHB number
based on device-tree properties"), added code to read a 64-bit property
from the device tree, and if not found read a 32-bit property (reg).

There was a bug in the 32-bit case, on big endian machines, due to the
use of the 64-bit value to read the 32-bit property. The cast of &prop
means we end up writing to the high 32-bit of prop, leaving the low
32-bits containing whatever junk was on the stack.

If that junk value was non-zero, and < MAX_PHBS, we would end up using
it as the PHB id. This results in users seeing what appear to be random
PHB ids.

Fix it by reading into a u32 property and then assigning that to the
u64 value, letting the CPU do the correct conversions for us.

Fixes: 63a72284b159 ("powerpc/pci: Assign fixed PHB number based on device-tree properties")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index a5c0153ede37f21d6dd8f47beac764587789fbc5..7fdf324d5b51f4ebb8716dfadda4ed40fb34d23d 100644 (file)
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -78,6 +78,7 @@ EXPORT_SYMBOL(get_pci_dma_ops);
 static int get_phb_number(struct device_node *dn)
 {
        int ret, phb_id = -1;
+       u32 prop_32;
        u64 prop;
 
        /*
@@ -86,8 +87,10 @@ static int get_phb_number(struct device_node *dn)
         * reading "ibm,opal-phbid", only present in OPAL environment.
         */
        ret = of_property_read_u64(dn, "ibm,opal-phbid", &prop);
-       if (ret)
-               ret = of_property_read_u32_index(dn, "reg", 1, (u32 *)&prop);
+       if (ret) {
+               ret = of_property_read_u32_index(dn, "reg", 1, &prop_32);
+               prop = prop_32;
+       }
 
        if (!ret)
                phb_id = (int)(prop & (MAX_PHBS - 1));