powerpc/cell: Fixed IOMMU mapping uses weak ordering for a pcie endpoint

At the moment the fixed mapping is by default strongly ordered (the
iommu_fixed=weak boot option must be used to make the fixed mapping weakly
ordered). If we're on a setup where the southbridge is being used in
endpoint mode (triblade and CAB boards) the default should be a weakly
ordered fixed mapping.

This adds a check so that if a node of type pcie-endpoint can be found in
the device tree the fixed mapping is set to be weak by default (but can be
overridden using iommu_fixed=strong).

Signed-off-by: Mark Nelson <markn@au1.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/cell/iommu.c

@@ -1150,12 +1150,23 @@ static int iommu_fixed_disabled;
 
 static int __init setup_iommu_fixed(char *str)
 {
+	struct device_node *pciep;
+
 	if (strcmp(str, "off") == 0)
 		iommu_fixed_disabled = 1;
 
-	else if (strcmp(str, "weak") == 0)
+	/* If we can find a pcie-endpoint in the device tree assume that
+	 * we're on a triblade or a CAB so by default the fixed mapping
+	 * should be set to be weakly ordered; but only if the boot
+	 * option WASN'T set for strong ordering
+	 */
+	pciep = of_find_node_by_type(NULL, "pcie-endpoint");
+
+	if (strcmp(str, "weak") == 0 || (pciep && strcmp(str, "strong") != 0))
 		iommu_fixed_is_weak = 1;
 
+	of_node_put(pciep);
+
 	return 1;
 }
 __setup("iommu_fixed=", setup_iommu_fixed);