swiotlb: add documentation and rename swiotlb_do_find_slots()

Add some kernel-doc comments and move the existing documentation of struct
io_tlb_slot to its correct location. The latter was forgotten in commit
942a818 ("swiotlb: move struct io_tlb_slot to swiotlb.c").

Use the opportunity to give swiotlb_do_find_slots() a more descriptive name
and make it clear how it differs from swiotlb_find_slots().

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: Petr Tesarik

include/linux/swiotlb.h

@@ -76,10 +76,6 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t phys,
  * @nslabs:	The number of IO TLB blocks (in groups of 64) between @start and
  *		@end. For default swiotlb, this is command line adjustable via
  *		setup_io_tlb_npages.
- * @list:	The free list describing the number of free entries available
- *		from each index.
- * @orig_addr:	The original address corresponding to a mapped entry.
- * @alloc_size:	Size of the allocated buffer.
  * @debugfs:	The dentry to debugfs.
  * @late_alloc:	%true if allocated using the page allocator
  * @force_bounce: %true if swiotlb bouncing is forced
@@ -111,6 +107,17 @@ struct io_tlb_mem {
 #endif
 };
 
+/**
+ * is_swiotlb_buffer() - check if a physical address belongs to a swiotlb
+ * @dev:        Device which has mapped the buffer.
+ * @paddr:      Physical address within the DMA buffer.
+ *
+ * Check if @paddr points into a bounce buffer.
+ *
+ * Return:
+ * * %true if @paddr points into a bounce buffer
+ * * %false otherwise
+ */
 static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
 {
 	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;

kernel/dma/swiotlb.c

@@ -62,6 +62,13 @@
 
 #define INVALID_PHYS_ADDR (~(phys_addr_t)0)
 
+/**
+ * struct io_tlb_slot - IO TLB slot descriptor
+ * @orig_addr:	The original address corresponding to a mapped entry.
+ * @alloc_size:	Size of the allocated buffer.
+ * @list:	The free list describing the number of free entries available
+ *		from each index.
+ */
 struct io_tlb_slot {
 	phys_addr_t orig_addr;
 	size_t alloc_size;
@@ -635,11 +642,22 @@ static void dec_used(struct io_tlb_mem *mem, unsigned int nslots)
 }
 #endif /* CONFIG_DEBUG_FS */
 
-/*
- * Find a suitable number of IO TLB entries size that will fit this request and
- * allocate a buffer from that IO TLB pool.
+/**
+ * swiotlb_area_find_slots() - search for slots in one IO TLB memory area
+ * @dev:	Device which maps the buffer.
+ * @area_index:	Index of the IO TLB memory area to be searched.
+ * @orig_addr:	Original (non-bounced) IO buffer address.
+ * @alloc_size: Total requested size of the bounce buffer,
+ *		including initial alignment padding.
+ * @alloc_align_mask:	Required alignment of the allocated buffer.
+ *
+ * Find a suitable sequence of IO TLB entries for the request and allocate
+ * a buffer from the given IO TLB memory area.
+ * This function takes care of locking.
+ *
+ * Return: Index of the first allocated slot, or -1 on error.
  */
-static int swiotlb_do_find_slots(struct device *dev, int area_index,
+static int swiotlb_area_find_slots(struct device *dev, int area_index,
 		phys_addr_t orig_addr, size_t alloc_size,
 		unsigned int alloc_align_mask)
 {
@@ -734,6 +752,19 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
 	return slot_index;
 }
 
+/**
+ * swiotlb_find_slots() - search for slots in the whole swiotlb
+ * @dev:	Device which maps the buffer.
+ * @orig_addr:	Original (non-bounced) IO buffer address.
+ * @alloc_size: Total requested size of the bounce buffer,
+ *		including initial alignment padding.
+ * @alloc_align_mask:	Required alignment of the allocated buffer.
+ *
+ * Search through the whole software IO TLB to find a sequence of slots that
+ * match the allocation constraints.
+ *
+ * Return: Index of the first allocated slot, or -1 on error.
+ */
 static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
 		size_t alloc_size, unsigned int alloc_align_mask)
 {
@@ -742,8 +773,8 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
 	int i = start, index;
 
 	do {
-		index = swiotlb_do_find_slots(dev, i, orig_addr, alloc_size,
-					      alloc_align_mask);
+		index = swiotlb_area_find_slots(dev, i, orig_addr, alloc_size,
+						alloc_align_mask);
 		if (index >= 0)
 			return index;
 		if (++i >= mem->nareas)
@@ -755,13 +786,31 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
 
 #ifdef CONFIG_DEBUG_FS
 
+/**
+ * mem_used() - get number of used slots in an allocator
+ * @mem:	Software IO TLB allocator.
+ *
+ * The result is accurate in this version of the function, because an atomic
+ * counter is available if CONFIG_DEBUG_FS is set.
+ *
+ * Return: Number of used slots.
+ */
 static unsigned long mem_used(struct io_tlb_mem *mem)
 {
 	return atomic_long_read(&mem->total_used);
 }
 
 #else /* !CONFIG_DEBUG_FS */
 
+/**
+ * mem_used() - get number of used slots in an allocator
+ * @mem:	Software IO TLB allocator.
+ *
+ * The result is not accurate, because there is no locking of individual
+ * areas.
+ *
+ * Return: Approximate number of used slots.
+ */
 static unsigned long mem_used(struct io_tlb_mem *mem)
 {
 	int i;