drm/i915: document range_overflows() and range_end_overflows() macros

Document the macros in preparation for making them more generally
available.

Cc: Kees Cook <kees@kernel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-hardening@vger.kernel.org
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/20250829174601.2163064-2-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Author: jnikula

drivers/gpu/drm/i915/i915_utils.h

@@ -67,6 +67,18 @@ bool i915_error_injected(void);
 		drm_err(&(i915)->drm, fmt, ##__VA_ARGS__); \
 })
 
+/**
+ * range_overflows() - Check if a range is out of bounds
+ * @start: Start of the range.
+ * @size:  Size of the range.
+ * @max:   Exclusive upper boundary.
+ *
+ * A strict check to determine if the range [@start, @start + @size) is
+ * invalid with respect to the allowable range [0, @max). Any range
+ * starting at or beyond @max is considered an overflow, even if @size is 0.
+ *
+ * Returns: true if the range is out of bounds.
+ */
 #define range_overflows(start, size, max) ({ \
 	typeof(start) start__ = (start); \
 	typeof(size) size__ = (size); \
@@ -76,9 +88,32 @@ bool i915_error_injected(void);
 	start__ >= max__ || size__ > max__ - start__; \
 })
 
+/**
+ * range_overflows_t() - Check if a range is out of bounds
+ * @type:  Data type to use.
+ * @start: Start of the range.
+ * @size:  Size of the range.
+ * @max:   Exclusive upper boundary.
+ *
+ * Same as range_overflows() but forcing the parameters to @type.
+ *
+ * Returns: true if the range is out of bounds.
+ */
 #define range_overflows_t(type, start, size, max) \
 	range_overflows((type)(start), (type)(size), (type)(max))
 
+/**
+ * range_end_overflows() - Check if a range's endpoint is out of bounds
+ * @start: Start of the range.
+ * @size:  Size of the range.
+ * @max:   Exclusive upper boundary.
+ *
+ * Checks only if the endpoint of a range (@start + @size) exceeds @max.
+ * Unlike range_overflows(), a zero-sized range at the boundary (@start == @max)
+ * is not considered an overflow. Useful for iterator-style checks.
+ *
+ * Returns: true if the endpoint exceeds the boundary.
+ */
 #define range_end_overflows(start, size, max) ({ \
 	typeof(start) start__ = (start); \
 	typeof(size) size__ = (size); \
@@ -88,6 +123,17 @@ bool i915_error_injected(void);
 	start__ > max__ || size__ > max__ - start__; \
 })
 
+/**
+ * range_end_overflows_t() - Check if a range's endpoint is out of bounds
+ * @type:  Data type to use.
+ * @start: Start of the range.
+ * @size:  Size of the range.
+ * @max:   Exclusive upper boundary.
+ *
+ * Same as range_end_overflows() but forcing the parameters to @type.
+ *
+ * Returns: true if the endpoint exceeds the boundary.
+ */
 #define range_end_overflows_t(type, start, size, max) \
 	range_end_overflows((type)(start), (type)(size), (type)(max))