x86/mm: Improve documentation for low-level device I/O functions

Add kerneldoc comments for memcpy_{to,from}io() and memset_io().  The
existing documentation for ioremap() was distant from the definition,
causing kernel-doc to miss it; move it appropriately.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170127161752.0b95e95b@lwn.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/io.h

@@ -164,6 +164,17 @@ static inline unsigned int isa_virt_to_bus(volatile void *address)
 #define virt_to_bus virt_to_phys
 #define bus_to_virt phys_to_virt
 
+/*
+ * The default ioremap() behavior is non-cached; if you need something
+ * else, you probably want one of the following.
+ */
+extern void __iomem *ioremap_nocache(resource_size_t offset, unsigned long size);
+extern void __iomem *ioremap_uc(resource_size_t offset, unsigned long size);
+#define ioremap_uc ioremap_uc
+
+extern void __iomem *ioremap_cache(resource_size_t offset, unsigned long size);
+extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, unsigned long prot_val);
+
 /**
  * ioremap     -   map bus memory into CPU space
  * @offset:    bus address of the memory
@@ -178,17 +189,6 @@ static inline unsigned int isa_virt_to_bus(volatile void *address)
  * If the area you are trying to map is a PCI BAR you should have a
  * look at pci_iomap().
  */
-extern void __iomem *ioremap_nocache(resource_size_t offset, unsigned long size);
-extern void __iomem *ioremap_uc(resource_size_t offset, unsigned long size);
-#define ioremap_uc ioremap_uc
-
-extern void __iomem *ioremap_cache(resource_size_t offset, unsigned long size);
-extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size,
-				unsigned long prot_val);
-
-/*
- * The default ioremap() behavior is non-cached:
- */
 static inline void __iomem *ioremap(resource_size_t offset, unsigned long size)
 {
 	return ioremap_nocache(offset, size);
@@ -207,18 +207,42 @@ extern void set_iounmap_nonlazy(void);
  */
 #define xlate_dev_kmem_ptr(p)	p
 
+/**
+ * memset_io	Set a range of I/O memory to a constant value
+ * @addr:	The beginning of the I/O-memory range to set
+ * @val:	The value to set the memory to
+ * @count:	The number of bytes to set
+ *
+ * Set a range of I/O memory to a given value.
+ */
 static inline void
 memset_io(volatile void __iomem *addr, unsigned char val, size_t count)
 {
 	memset((void __force *)addr, val, count);
 }
 
+/**
+ * memcpy_fromio	Copy a block of data from I/O memory
+ * @dst:		The (RAM) destination for the copy
+ * @src:		The (I/O memory) source for the data
+ * @count:		The number of bytes to copy
+ *
+ * Copy a block of data from I/O memory.
+ */
 static inline void
 memcpy_fromio(void *dst, const volatile void __iomem *src, size_t count)
 {
 	memcpy(dst, (const void __force *)src, count);
 }
 
+/**
+ * memcpy_toio		Copy a block of data into I/O memory
+ * @dst:		The (I/O memory) destination for the copy
+ * @src:		The (RAM) source for the data
+ * @count:		The number of bytes to copy
+ *
+ * Copy a block of data to I/O memory.
+ */
 static inline void
 memcpy_toio(volatile void __iomem *dst, const void *src, size_t count)
 {