[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
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -47,6 +47,8 @@
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 @@
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 @@
return 1;
}
+__setup("protect4gb=", setup_protect4gb);
__setup("iommu=", setup_iommu);
static unsigned long iommu_range_alloc(struct iommu_table *tbl,
@@ -439,6 +452,9 @@
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 @@
#ifdef CONFIG_CRASH_DUMP
if (ppc_md.tce_get) {
- unsigned long index, tceval;
+ unsigned long tceval;
unsigned long tcecount = 0;
/*
@@ -490,6 +506,23 @@
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");