[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>

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index c50d707..d2598e2 100644 (file)
--- 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");