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From:   Petr Tesarik <petrtesarik@huaweicloud.com>
To:     Stefano Stabellini <sstabellini@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
        x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        "H. Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Petr Tesarik <petr.tesarik.ext@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
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        linux-mips@vger.kernel.org (open list:MIPS),
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Cc:     Roberto Sassu <roberto.sassu@huaweicloud.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, petr@tesarici.cz
Subject: [PATCH v4 2/8] swiotlb: add documentation and rename swiotlb_do_find_slots()
Date:   Thu, 13 Jul 2023 17:23:13 +0200
Message-Id: <11826bfbc148771ab36d0b485558aa52cbdd204f.1689261692.git.petr.tesarik.ext@huawei.com>
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From: Petr Tesarik <petr.tesarik.ext@huawei.com>

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@huawei.com>
---
 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