arm64: Fix cache maintenance function comments

Fix and expand comments for the cache maintenance functions in
cacheflush.h. Adds comments to functions that weren't described
before. Explains what the functions do using Arm Architecture
Reference Manual terminology.

No functional change intended.

Acked-by: Mark Rutland <[e-mail]>
Signed-off-by: Fuad Tabba <[e-mail]>
Reviewed-by: Ard Biesheuvel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/include/asm/cacheflush.h

···
  *	the implementation assumes non-aliasing VIPT D-cache and (aliasing)
  *	VIPT I-cache.
  *
- *	flush_icache_range(start, end)
+ *	All functions below apply to the interval [start, end)
+ *		- start  - virtual start address (inclusive)
+ *		- end    - virtual end address (exclusive)
  *
- *		Ensure coherency between the I-cache and the D-cache in the
- *		region described by start, end.
- *		- start  - virtual start address
- *		- end    - virtual end address
+ *	__flush_icache_range(start, end)
  *
- *	invalidate_icache_range(start, end)
- *
- *		Invalidate the I-cache in the region described by start, end.
- *		- start  - virtual start address
- *		- end    - virtual end address
+ *		Ensure coherency between the I-cache and the D-cache region to
+ *		the Point of Unification.
  *
  *	__flush_cache_user_range(start, end)
  *
- *		Ensure coherency between the I-cache and the D-cache in the
- *		region described by start, end.
- *		- start  - virtual start address
- *		- end    - virtual end address
+ *		Ensure coherency between the I-cache and the D-cache region to
+ *		the Point of Unification.
+ *		Use only if the region might access user memory.
+ *
+ *	invalidate_icache_range(start, end)
+ *
+ *		Invalidate I-cache region to the Point of Unification.
  *
  *	__flush_dcache_area(start, end)
  *
- *		Ensure that the data held in page is written back.
- *		- start  - virtual start address
- *		- end    - virtual end address
+ *		Clean and invalidate D-cache region to the Point of Coherency.
+ *
+ *	__inval_dcache_area(start, end)
+ *
+ *		Invalidate D-cache region to the Point of Coherency.
+ *
+ *	__clean_dcache_area_poc(start, end)
+ *
+ *		Clean D-cache region to the Point of Coherency.
+ *
+ *	__clean_dcache_area_pop(start, end)
+ *
+ *		Clean D-cache region to the Point of Persistence.
+ *
+ *	__clean_dcache_area_pou(start, end)
+ *
+ *		Clean D-cache region to the Point of Unification.
  */
 extern void __flush_icache_range(unsigned long start, unsigned long end);
 extern void invalidate_icache_range(unsigned long start, unsigned long end);