[PATCH v4 2/8] swiotlb: add documentation and rename swiotlb_do_find_slots()

[Petr Tesarik <petrtesarik@xxxxxxxxxxxxxxx>]

From: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx>

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
942a8186eb445 ("swiotlb: move struct io_tlb_slot to swiotlb.c").

Use the opportunity to give swiotlb_do_find_slots() a more descriptive
name, which makes it clear how it differs from swiotlb_find_slots().

Signed-off-by: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx>
---
 include/linux/swiotlb.h | 15 +++++++---
 kernel/dma/swiotlb.c    | 61 +++++++++++++++++++++++++++++++++++++----
 2 files changed, 66 insertions(+), 10 deletions(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 07216af59e93..39313c3a791a 100644
--- a/include/linux/swiotlb.h
+++ b/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;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 873b077d7e37..01161d040639 100644
--- a/kernel/dma/swiotlb.c
+++ b/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;
@@ -632,11 +639,22 @@ 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.
+/**
+ * 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 area_find_slots(struct device *dev, int area_index,
                phys_addr_t orig_addr, size_t alloc_size,
                unsigned int alloc_align_mask)
 {
@@ -731,6 +749,19 @@ 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)
 {
@@ -739,8 +770,8 @@ 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 = area_find_slots(dev, i, orig_addr, alloc_size,
+                                       alloc_align_mask);
                if (index >= 0)
                        return index;
                if (++i >= mem->nareas)
@@ -752,6 +783,15 @@ 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);
@@ -759,6 +799,15 @@ static unsigned long mem_used(struct io_tlb_mem *mem)
 
 #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;
-- 
2.25.1