[POWERPC] DMA 4GB boundary protection

There are many adapters which cannot handle DMAing across any 4 GB
boundary.  For instance, the latest Emulex adapters.

This normally is not an issue as firmware gives dma-windows under
4gigs.  However, some of the new System-P boxes have dma-windows above
4gigs, and this present a problem.

During initialization of the IOMMU tables, the last entry at each 4GB
boundary is marked as used.  Thus no mappings can cross the boundary.
If a table ends at a 4GB boundary, the entry is not marked as used.

A boot option to remove this 4GB protection is given w/ protect4gb=off.
This exposes the potential issue for driver and hardware development
purposes.

Signed-off-by: Jake Moilanen <moilanen@austin.ibm.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 34 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index c50d7072f305..d2598e2e7bbe 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -47,6 +47,8 @@ static int novmerge = 0;
 static int novmerge = 1;
 #endif
 
+static int protect4gb = 1;
+
 static inline unsigned long iommu_num_pages(unsigned long vaddr,
                                             unsigned long slen)
 {
@@ -58,6 +60,16 @@ static inline unsigned long iommu_num_pages(unsigned long vaddr,
         return npages;
 }
 
+static int __init setup_protect4gb(char *str)
+{
+        if (strcmp(str, "on") == 0)
+                protect4gb = 1;
+        else if (strcmp(str, "off") == 0)
+                protect4gb = 0;
+
+        return 1;
+}
+
 static int __init setup_iommu(char *str)
 {
         if (!strcmp(str, "novmerge"))
@@ -67,6 +79,7 @@ static int __init setup_iommu(char *str)
         return 1;
 }
 
+__setup("protect4gb=", setup_protect4gb);
 __setup("iommu=", setup_iommu);
 
 static unsigned long iommu_range_alloc(struct iommu_table *tbl,
@@ -439,6 +452,9 @@ void iommu_unmap_sg(struct iommu_table *tbl, struct scatterlist *sglist,
 struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid)
 {
         unsigned long sz;
+        unsigned long start_index, end_index;
+        unsigned long entries_per_4g;
+        unsigned long index;
         static int welcomed = 0;
         struct page *page;
 
@@ -460,7 +476,7 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid)
 
 #ifdef CONFIG_CRASH_DUMP
         if (ppc_md.tce_get) {
-                unsigned long index, tceval;
+                unsigned long tceval;
                 unsigned long tcecount = 0;
 
                 /*
@@ -490,6 +506,23 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid)
         ppc_md.tce_free(tbl, tbl->it_offset, tbl->it_size);
 #endif
 
+        /*
+         * DMA cannot cross 4 GB boundary.  Mark last entry of each 4
+         * GB chunk as reserved.
+         */
+        if (protect4gb) {
+                entries_per_4g = 0x100000000l >> IOMMU_PAGE_SHIFT;
+
+                /* Mark the last bit before a 4GB boundary as used */
+                start_index = tbl->it_offset | (entries_per_4g - 1);
+                start_index -= tbl->it_offset;
+
+                end_index = tbl->it_size;
+
+                for (index = start_index; index < end_index - 1; index += entries_per_4g)
+                        __set_bit(index, tbl->it_map);
+        }
+
         if (!welcomed) {
                 printk(KERN_INFO "IOMMU table initialized, virtual merging %s\n",
                        novmerge ? "disabled" : "enabled");