cifs: clarify comment about timestamp granularity for old servers

It could be confusing why we set granularity to 1 seconds rather
than 2 seconds (1 second is the max the VFS allows) for these
mounts to very old servers ...
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsfs.c

@@ -169,7 +169,13 @@ cifs_read_super(struct super_block *sb)
 	else
 		sb->s_maxbytes = MAX_NON_LFS;
 
-	/* Some very old servers like DOS and OS/2 used 2 second granularity */
+	/*
+	 * Some very old servers like DOS and OS/2 used 2 second granularity
+	 * (while all current servers use 100ns granularity - see MS-DTYP)
+	 * but 1 second is the maximum allowed granularity for the VFS
+	 * so for old servers set time granularity to 1 second while for
+	 * everything else (current servers) set it to 100ns.
+	 */
 	if ((tcon->ses->server->vals->protocol_id == SMB10_PROT_ID) &&
 	    ((tcon->ses->capabilities &
 	      tcon->ses->server->vals->cap_nt_find) == 0) &&