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Commit 56997559 authored by Jake Moilanen's avatar Jake Moilanen Committed by Paul Mackerras
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[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: default avatarJake Moilanen <moilanen@austin.ibm.com>
Acked-by: default avatarOlof Johansson <olof@lixom.net>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 1f9209cf

arch/powerpc/kernel/iommu.c

+34 −1
Original line number Diff line number Diff line
@@ -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");