[PATCH] powerpc: Enhance pmem DMA bypass handling

[Brian King]

If ibm,pmemory is installed in the system, it can appear anywhere
in the address space. This patch enhances how we handle DMA for devices when
ibm,pmemory is present. In the case where we have enough DMA space to
direct map all of RAM, but not ibm,pmemory, we use direct DMA for
I/O to RAM and use the default window to dynamically map ibm,pmemory.
In the case where we only have a single DMA window, this won't work,
so if the window is not big enough to map the entire address range,
we cannot direct map.

Signed-off-by: Brian King <brking at linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 269f61d519c2..d9ae985d10a4 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1092,15 +1092,6 @@ static phys_addr_t ddw_memory_hotplug_max(void)
 	phys_addr_t max_addr = memory_hotplug_max();
 	struct device_node *memory;
 
-	/*
-	 * The "ibm,pmemory" can appear anywhere in the address space.
-	 * Assuming it is still backed by page structs, set the upper limit
-	 * for the huge DMA window as MAX_PHYSMEM_BITS.
-	 */
-	if (of_find_node_by_type(NULL, "ibm,pmemory"))
-		return (sizeof(phys_addr_t) * 8 <= MAX_PHYSMEM_BITS) ?
-			(phys_addr_t) -1 : (1ULL << MAX_PHYSMEM_BITS);
-
 	for_each_node_by_type(memory, "memory") {
 		unsigned long start, size;
 		int n_mem_addr_cells, n_mem_size_cells, len;
@@ -1341,6 +1332,16 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	 */
 	len = max_ram_len;
 	if (pmem_present) {
+		if (default_win_removed) {
+			/*
+			 * If we only have one DMA window and have pmem present,
+			 * then we need to be able to map the entire address
+			 * range in order to be able to do direct DMA to RAM.
+			 */
+			len = order_base_2((sizeof(phys_addr_t) * 8 <= MAX_PHYSMEM_BITS) ?
+					(phys_addr_t) -1 : (1ULL << MAX_PHYSMEM_BITS));
+		}
+
 		if (query.largest_available_block >=
 		    (1ULL << (MAX_PHYSMEM_BITS - page_shift)))
 			len = MAX_PHYSMEM_BITS;
-- 
2.27.0