swiotlb: allow architectures to override swiotlb pool allocation

Architectures may need to allocate memory specially for use with the swiotlb. Create the weak function swiotlb_alloc_boot() and swiotlb_alloc() defaulting to the current behaviour.

---
include/linux/swiotlb.h | 3 +++
lib/swiotlb.c | 15 ++++++++++++---

2 files changed, 15 insertions(+), 3 deletions(-)

===================================================================

@@ -2,6 +2,9 @@

#define LINUX__SWIOTLB_H

#include <asm/swiotlb.h>
+
+extern void *swiotlb_alloc_boot(size_t bytes);
+extern void *swiotlb_alloc(unsigned order);

/* SWIOTLB interface */

===================================================================

@@ -127,6 +127,16 @@

__setup("swiotlb=", setup_io_tlb_npages);
/* make io_tlb_overflow tunable too? */

+void * __weak swiotlb_alloc_boot(size_t size)
+{
+ return alloc_bootmem_low_pages(size);
+}
+
+void * __weak swiotlb_alloc(unsigned order)
+{
+ return (void *)__get_free_pages(GFP_DMA | __GFP_NOWARN, order);
+}
+
/*
* Statically reserve bounce buffer space and initialize bounce buffer data
* structures for the software IO TLB used to implement the DMA API.
@@ -146,7 +156,7 @@

	/*
	 * Get IO TLB memory from the low pages
	 */
-	io_tlb_start = alloc_bootmem_low_pages(bytes);
+	io_tlb_start = swiotlb_alloc_boot(bytes);
	if (!io_tlb_start)
		panic("Cannot allocate SWIOTLB buffer");
	io_tlb_end = io_tlb_start + bytes;
@@ -203,8 +213,7 @@
	bytes = io_tlb_nslabs << IO_TLB_SHIFT;

	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
-		io_tlb_start = (char *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
-		                                        order);
+		io_tlb_start = swiotlb_alloc(order);
		if (io_tlb_start)
			break;
		order--;