[IA64] hooks to wait for mmio writes to drain when migrating processes

On SN2, MMIO writes which are issued from separate processors are not
guaranteed to arrive in any particular order at the IO hardware.  When
performing such writes from the kernel this is not a problem, as a
kernel thread will not migrate to another CPU during execution, and
mmiowb() calls can guarantee write ordering when control of the IO
resource is allowed to move between threads.

However, when MMIO writes can be performed from user space (e.g. DRM)
there are no such guarantees and mechanisms, as the process may
context-switch at any time, and may migrate to a different CPU as part
of the switch.  For such programs/hardware to operate correctly, it is
required that the MMIO writes from the old CPU be accepted by the IO
hardware before subsequent writes from the new CPU can be issued.

The following patch implements this behavior on SN2 by waiting for a
Shub register to indicate that these writes have been accepted.  This
is placed in the context switch-in path, and only performs the wait
when the newly scheduled task changes CPUs.

Signed-off-by: Prarit Bhargava <prarit@sgi.com>
Signed-off-by: Brent Casavant <bcasavan@sgi.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/asm-ia64/machvec_sn2.h b/include/asm-ia64/machvec_sn2.h
index e1b6cd63f49e..6f0021bb3874 100644
--- a/include/asm-ia64/machvec_sn2.h
+++ b/include/asm-ia64/machvec_sn2.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2002-2003 Silicon Graphics, Inc.  All Rights Reserved.
+ * Copyright (c) 2002-2003,2006 Silicon Graphics, Inc.  All Rights Reserved.
  * 
  * This program is free software; you can redistribute it and/or modify it 
  * under the terms of version 2 of the GNU General Public License 
@@ -71,6 +71,7 @@ extern ia64_mv_dma_sync_single_for_device sn_dma_sync_single_for_device;
 extern ia64_mv_dma_sync_sg_for_device   sn_dma_sync_sg_for_device;
 extern ia64_mv_dma_mapping_error        sn_dma_mapping_error;
 extern ia64_mv_dma_supported            sn_dma_supported;
+extern ia64_mv_migrate_t                sn_migrate;
 
 /*
  * This stuff has dual use!
@@ -120,6 +121,7 @@ extern ia64_mv_dma_supported		sn_dma_supported;
 #define platform_dma_sync_sg_for_device sn_dma_sync_sg_for_device
 #define platform_dma_mapping_error              sn_dma_mapping_error
 #define platform_dma_supported          sn_dma_supported
+#define platform_migrate                sn_migrate
 
 #include <asm/sn/io.h>