From 0bcf55800fb3d3baf41c9681c067153a4b3742ce Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Mon, 26 Nov 2012 09:36:57 +0100
Subject: [PATCH] Eagerly map DMA buffers

This patch is a work-around for issue #452.
---
 os/include/os/attached_ram_dataspace.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/os/include/os/attached_ram_dataspace.h b/os/include/os/attached_ram_dataspace.h
index 9ac439e919..f93db613d0 100644
--- a/os/include/os/attached_ram_dataspace.h
+++ b/os/include/os/attached_ram_dataspace.h
@@ -22,6 +22,7 @@
 #define _INCLUDE__OS__ATTACHED_RAM_DATASPACE_H_
 
 #include <ram_session/ram_session.h>
+#include <util/touch.h>
 #include <base/env.h>
 
 namespace Genode {
@@ -61,6 +62,23 @@ namespace Genode {
 					_ram_session->free(_ds);
 					throw;
 				}
+
+				/*
+				 * Eagerly map dataspace if used for DMA
+				 *
+				 * On some platforms, namely Fiasco.OC on ARMv7, the handling
+				 * of page faults interferes with the caching attributes used
+				 * for uncached DMA memory. See issue #452 for more details
+				 * (https://github.com/genodelabs/genode/issues/452). As a
+				 * work-around for this issues, we eagerly map the whole
+				 * dataspace before writing actual content to it.
+				 */
+				if (!_cached) {
+					enum { PAGE_SIZE = 4096 };
+					unsigned char volatile *base = (unsigned char volatile *)_local_addr;
+					for (size_t i = 0; i < _size; i += PAGE_SIZE)
+						touch_read_write(base + i);
+				}
 			}
 
 		public: