iommu/dma: Explicitly sort PCI DMA windows

Originally, creating the dma_ranges resource list in pre-sorted fashion
was the simplest and most efficient way to enforce the order required by
iova_reserve_pci_windows(). However since then at least one PCI host
driver is now re-sorting the list for its own probe-time processing,
which doesn't seem entirely unreasonable, so that basic assumption no
longer holds. Make iommu-dma robust and get the sort order it needs by
explicitly sorting, which means we can also save the effort at creation
time and just build the list in whatever natural order the DT had.

Signed-off-by: Robin Murphy <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/3566[e-mail]
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/dma-iommu.c

···
 #include <linux/iommu.h>
 #include <linux/iova.h>
 #include <linux/irq.h>
+#include <linux/list_sort.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/pci.h>
···
 	return 0;
 }
 
+static int iommu_dma_ranges_sort(void *priv, const struct list_head *a,
+		const struct list_head *b)
+{
+	struct resource_entry *res_a = list_entry(a, typeof(*res_a), node);
+	struct resource_entry *res_b = list_entry(b, typeof(*res_b), node);
+
+	return res_a->res->start > res_b->res->start;
+}
+
 static int iova_reserve_pci_windows(struct pci_dev *dev,
 		struct iova_domain *iovad)
 {
···
 	}
 
 	/* Get reserved DMA windows from host bridge */
+	list_sort(NULL, &bridge->dma_ranges, iommu_dma_ranges_sort);
 	resource_list_for_each_entry(window, &bridge->dma_ranges) {
 		end = window->res->start - window->offset;
 resv_iova:
···
 			hi = iova_pfn(iovad, end);
 			reserve_iova(iovad, lo, hi);
 		} else if (end < start) {
-			/* dma_ranges list should be sorted */
+			/* DMA ranges should be non-overlapping */
 			dev_err(&dev->dev,
 				"Failed to reserve IOVA [%pa-%pa]\n",
 				&start, &end);

drivers/pci/of.c

···
 
 	dev_dbg(dev, "Parsing dma-ranges property...\n");
 	for_each_of_pci_range(&parser, &range) {
-		struct resource_entry *entry;
 		/*
 		 * If we failed translation or got a zero-sized region
 		 * then skip this range
···
 			goto failed;
 		}
 
-		/* Keep the resource list sorted */
-		resource_list_for_each_entry(entry, ib_resources)
-			if (entry->res->start > res->start)
-				break;
-
-		pci_add_resource_offset(&entry->node, res,
+		pci_add_resource_offset(ib_resources, res,
 					res->start - range.pci_addr);
 	}