swiotlb: Make SWIOTLB_NO_FORCE perform no allocation

When SWIOTLB_NO_FORCE is used, there should really be no allocations of
default_nslabs to occur since we are not going to use those slabs. If a
platform was somehow setting swiotlb_no_force and a later call to
swiotlb_init() was to be made we would still be proceeding with
allocating the default SWIOTLB size (64MB), whereas if swiotlb=noforce
was set on the kernel command line we would have only allocated 2KB.

This would be inconsistent and the point of initializing default_nslabs
to 1, was intended to allocate the minimum amount of memory possible, so
simply remove that minimal allocation period.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

kernel/dma/swiotlb.c

@@ -83,12 +83,10 @@ setup_io_tlb_npages(char *str)
 	}
 	if (*str == ',')
 		++str;
-	if (!strcmp(str, "force")) {
+	if (!strcmp(str, "force"))
 		swiotlb_force = SWIOTLB_FORCE;
-	} else if (!strcmp(str, "noforce")) {
+	else if (!strcmp(str, "noforce"))
 		swiotlb_force = SWIOTLB_NO_FORCE;
-		default_nslabs = 1;
-	}
 
 	return 0;
 }
@@ -174,6 +172,9 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 	struct io_tlb_mem *mem;
 	size_t alloc_size;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		return 0;
+
 	/* protect against double initialization */
 	if (WARN_ON_ONCE(io_tlb_default_mem))
 		return -ENOMEM;
@@ -211,6 +212,9 @@ swiotlb_init(int verbose)
 	size_t bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
 	void *tlb;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		return;
+
 	/* Get IO TLB memory from the low pages */
 	tlb = memblock_alloc_low(bytes, PAGE_SIZE);
 	if (!tlb)
@@ -240,6 +244,9 @@ swiotlb_late_init_with_default_size(size_t default_size)
 	unsigned int order;
 	int rc = 0;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		return 0;
+
 	/*
 	 * Get IO TLB memory from the low pages
 	 */
@@ -276,6 +283,9 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	unsigned long bytes = nslabs << IO_TLB_SHIFT, i;
 	struct io_tlb_mem *mem;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		return 0;
+
 	/* protect against double initialization */
 	if (WARN_ON_ONCE(io_tlb_default_mem))
 		return -ENOMEM;