bounce: allow use of bounce pool via config option

The tilegx USB OHCI support needs the bounce pool since we're not
using the IOMMU to handle 32-bit addresses.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/Kconfig

@@ -406,6 +406,12 @@ config TILE_USB
 	  Provides USB host adapter support for the built-in EHCI and OHCI
 	  interfaces on TILE-Gx chips.
 
+# USB OHCI needs the bounce pool since tilegx will often have more
+# than 4GB of memory, but we don't currently use the IOTLB to present
+# a 32-bit address to OHCI.  So we need to use a bounce pool instead.
+config NEED_BOUNCE_POOL
+	def_bool USB_OHCI_HCD
+
 config HOTPLUG
 	bool "Support for hot-pluggable devices"
 	---help---

mm/bounce.c

@@ -24,23 +24,25 @@
 
 static mempool_t *page_pool, *isa_page_pool;
 
-#ifdef CONFIG_HIGHMEM
+#if defined(CONFIG_HIGHMEM) || defined(CONFIG_NEED_BOUNCE_POOL)
 static __init int init_emergency_pool(void)
 {
-#ifndef CONFIG_MEMORY_HOTPLUG
+#if defined(CONFIG_HIGHMEM) && !defined(CONFIG_MEMORY_HOTPLUG)
 	if (max_pfn <= max_low_pfn)
 		return 0;
 #endif
 
 	page_pool = mempool_create_page_pool(POOL_SIZE, 0);
 	BUG_ON(!page_pool);
-	printk("highmem bounce pool size: %d pages\n", POOL_SIZE);
+	printk("bounce pool size: %d pages\n", POOL_SIZE);
 
 	return 0;
 }
 
 __initcall(init_emergency_pool);
+#endif
 
+#ifdef CONFIG_HIGHMEM
 /*
  * highmem version, map in to vec
  */