powerpc/pseries/iommu: Check if the default window in use before removing it

At the moment this check is performed after we remove the default window
which is late and disallows to revert whatever changes enable_ddw()
has made to DMA windows.

This moves the check and error exit before removing the window.

This raised the message severity from "debug" to "warning" as this
should not happen in practice and cannot be triggered by the userspace.

Fixes: 381ceda8 ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020132315.2287178-4-aik@ozlabs.ru

arch/powerpc/platforms/pseries/iommu.c

@@ -1302,6 +1302,12 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 		struct property *default_win;
 		int reset_win_ext;
 
+		/* DDW + IOMMU on single window may fail if there is any allocation */
+		if (iommu_table_in_use(tbl)) {
+			dev_warn(&dev->dev, "current IOMMU table in use, can't be replaced.\n");
+			goto out_failed;
+		}
+
 		default_win = of_find_property(pdn, "ibm,dma-window", NULL);
 		if (!default_win)
 			goto out_failed;
@@ -1356,12 +1362,6 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 			query.largest_available_block,
 			1ULL << page_shift);
 
-		/* DDW + IOMMU on single window may fail if there is any allocation */
-		if (default_win_removed && iommu_table_in_use(tbl)) {
-			dev_dbg(&dev->dev, "current IOMMU table in use, can't be replaced.\n");
-			goto out_failed;
-		}
-
 		len = order_base_2(query.largest_available_block << page_shift);
 		win_name = DMA64_PROPNAME;
 	} else {