1 /*******************************************************************************
2 *
3 * Module Name: nsxfeval - Public interfaces to the ACPI subsystem
4 * ACPI Object evaluation interfaces
5 *
6 ******************************************************************************/
7
8 /*
9 * Copyright (C) 2000 - 2004, R. Byron Moore
10 * All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions, and the following disclaimer,
17 * without modification.
18 * 2. Redistributions in binary form must reproduce at minimum a disclaimer
19 * substantially similar to the "NO WARRANTY" disclaimer below
20 * ("Disclaimer") and any redistribution must be conditioned upon
21 * including a substantially similar Disclaimer requirement for further
22 * binary redistribution.
23 * 3. Neither the names of the above-listed copyright holders nor the names
24 * of any contributors may be used to endorse or promote products derived
25 * from this software without specific prior written permission.
26 *
27 * Alternatively, this software may be distributed under the terms of the
28 * GNU General Public License ("GPL") version 2 as published by the Free
29 * Software Foundation.
30 *
31 * NO WARRANTY
32 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
33 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
34 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
35 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
36 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
37 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
38 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
40 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
41 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
42 * POSSIBILITY OF SUCH DAMAGES.
43 */
44
45
46 #include <acpi/acpi.h>
47 #include <acpi/acnamesp.h>
48 #include <acpi/acinterp.h>
49
50
51 #define _COMPONENT ACPI_NAMESPACE
52 ACPI_MODULE_NAME ("nsxfeval")
53
54
55 /*******************************************************************************
56 *
57 * FUNCTION: acpi_evaluate_object_typed
58 *
59 * PARAMETERS: Handle - Object handle (optional)
60 * *Pathname - Object pathname (optional)
61 * **external_params - List of parameters to pass to method,
62 * terminated by NULL. May be NULL
63 * if no parameters are being passed.
64 * *return_buffer - Where to put method's return value (if
65 * any). If NULL, no value is returned.
66 * return_type - Expected type of return object
67 *
68 * RETURN: Status
69 *
70 * DESCRIPTION: Find and evaluate the given object, passing the given
71 * parameters if necessary. One of "Handle" or "Pathname" must
72 * be valid (non-null)
73 *
74 ******************************************************************************/
75
76 acpi_status
acpi_evaluate_object_typed(acpi_handle handle,acpi_string pathname,struct acpi_object_list * external_params,struct acpi_buffer * return_buffer,acpi_object_type return_type)77 acpi_evaluate_object_typed (
78 acpi_handle handle,
79 acpi_string pathname,
80 struct acpi_object_list *external_params,
81 struct acpi_buffer *return_buffer,
82 acpi_object_type return_type)
83 {
84 acpi_status status;
85 u8 must_free = FALSE;
86
87
88 ACPI_FUNCTION_TRACE ("acpi_evaluate_object_typed");
89
90
91 /* Return buffer must be valid */
92
93 if (!return_buffer) {
94 return_ACPI_STATUS (AE_BAD_PARAMETER);
95 }
96
97 if (return_buffer->length == ACPI_ALLOCATE_BUFFER) {
98 must_free = TRUE;
99 }
100
101 /* Evaluate the object */
102
103 status = acpi_evaluate_object (handle, pathname, external_params, return_buffer);
104 if (ACPI_FAILURE (status)) {
105 return_ACPI_STATUS (status);
106 }
107
108 /* Type ANY means "don't care" */
109
110 if (return_type == ACPI_TYPE_ANY) {
111 return_ACPI_STATUS (AE_OK);
112 }
113
114 if (return_buffer->length == 0) {
115 /* Error because caller specifically asked for a return value */
116
117 ACPI_DEBUG_PRINT ((ACPI_DB_ERROR,
118 "No return value\n"));
119
120 return_ACPI_STATUS (AE_NULL_OBJECT);
121 }
122
123 /* Examine the object type returned from evaluate_object */
124
125 if (((union acpi_object *) return_buffer->pointer)->type == return_type) {
126 return_ACPI_STATUS (AE_OK);
127 }
128
129 /* Return object type does not match requested type */
130
131 ACPI_DEBUG_PRINT ((ACPI_DB_ERROR,
132 "Incorrect return type [%s] requested [%s]\n",
133 acpi_ut_get_type_name (((union acpi_object *) return_buffer->pointer)->type),
134 acpi_ut_get_type_name (return_type)));
135
136 if (must_free) {
137 /* Caller used ACPI_ALLOCATE_BUFFER, free the return buffer */
138
139 acpi_os_free (return_buffer->pointer);
140 return_buffer->pointer = NULL;
141 }
142
143 return_buffer->length = 0;
144 return_ACPI_STATUS (AE_TYPE);
145 }
146
147
148 /*******************************************************************************
149 *
150 * FUNCTION: acpi_evaluate_object
151 *
152 * PARAMETERS: Handle - Object handle (optional)
153 * Pathname - Object pathname (optional)
154 * external_params - List of parameters to pass to method,
155 * terminated by NULL. May be NULL
156 * if no parameters are being passed.
157 * return_buffer - Where to put method's return value (if
158 * any). If NULL, no value is returned.
159 *
160 * RETURN: Status
161 *
162 * DESCRIPTION: Find and evaluate the given object, passing the given
163 * parameters if necessary. One of "Handle" or "Pathname" must
164 * be valid (non-null)
165 *
166 ******************************************************************************/
167
168 acpi_status
acpi_evaluate_object(acpi_handle handle,acpi_string pathname,struct acpi_object_list * external_params,struct acpi_buffer * return_buffer)169 acpi_evaluate_object (
170 acpi_handle handle,
171 acpi_string pathname,
172 struct acpi_object_list *external_params,
173 struct acpi_buffer *return_buffer)
174 {
175 acpi_status status;
176 acpi_status status2;
177 union acpi_operand_object **internal_params = NULL;
178 union acpi_operand_object *internal_return_obj = NULL;
179 acpi_size buffer_space_needed;
180 u32 i;
181
182
183 ACPI_FUNCTION_TRACE ("acpi_evaluate_object");
184
185
186 /*
187 * If there are parameters to be passed to the object
188 * (which must be a control method), the external objects
189 * must be converted to internal objects
190 */
191 if (external_params && external_params->count) {
192 /*
193 * Allocate a new parameter block for the internal objects
194 * Add 1 to count to allow for null terminated internal list
195 */
196 internal_params = ACPI_MEM_CALLOCATE (((acpi_size) external_params->count + 1) *
197 sizeof (void *));
198 if (!internal_params) {
199 return_ACPI_STATUS (AE_NO_MEMORY);
200 }
201
202 /*
203 * Convert each external object in the list to an
204 * internal object
205 */
206 for (i = 0; i < external_params->count; i++) {
207 status = acpi_ut_copy_eobject_to_iobject (&external_params->pointer[i],
208 &internal_params[i]);
209 if (ACPI_FAILURE (status)) {
210 acpi_ut_delete_internal_object_list (internal_params);
211 return_ACPI_STATUS (status);
212 }
213 }
214 internal_params[external_params->count] = NULL;
215 }
216
217 /*
218 * Three major cases:
219 * 1) Fully qualified pathname
220 * 2) No handle, not fully qualified pathname (error)
221 * 3) Valid handle
222 */
223 if ((pathname) &&
224 (acpi_ns_valid_root_prefix (pathname[0]))) {
225 /*
226 * The path is fully qualified, just evaluate by name
227 */
228 status = acpi_ns_evaluate_by_name (pathname, internal_params,
229 &internal_return_obj);
230 }
231 else if (!handle) {
232 /*
233 * A handle is optional iff a fully qualified pathname
234 * is specified. Since we've already handled fully
235 * qualified names above, this is an error
236 */
237 if (!pathname) {
238 ACPI_DEBUG_PRINT ((ACPI_DB_ERROR,
239 "Both Handle and Pathname are NULL\n"));
240 }
241 else {
242 ACPI_DEBUG_PRINT ((ACPI_DB_ERROR,
243 "Handle is NULL and Pathname is relative\n"));
244 }
245
246 status = AE_BAD_PARAMETER;
247 }
248 else {
249 /*
250 * We get here if we have a handle -- and if we have a
251 * pathname it is relative. The handle will be validated
252 * in the lower procedures
253 */
254 if (!pathname) {
255 /*
256 * The null pathname case means the handle is for
257 * the actual object to be evaluated
258 */
259 status = acpi_ns_evaluate_by_handle (handle, internal_params,
260 &internal_return_obj);
261 }
262 else {
263 /*
264 * Both a Handle and a relative Pathname
265 */
266 status = acpi_ns_evaluate_relative (handle, pathname, internal_params,
267 &internal_return_obj);
268 }
269 }
270
271
272 /*
273 * If we are expecting a return value, and all went well above,
274 * copy the return value to an external object.
275 */
276 if (return_buffer) {
277 if (!internal_return_obj) {
278 return_buffer->length = 0;
279 }
280 else {
281 if (ACPI_GET_DESCRIPTOR_TYPE (internal_return_obj) == ACPI_DESC_TYPE_NAMED) {
282 /*
283 * If we received a NS Node as a return object, this means that
284 * the object we are evaluating has nothing interesting to
285 * return (such as a mutex, etc.) We return an error because
286 * these types are essentially unsupported by this interface.
287 * We don't check up front because this makes it easier to add
288 * support for various types at a later date if necessary.
289 */
290 status = AE_TYPE;
291 internal_return_obj = NULL; /* No need to delete a NS Node */
292 return_buffer->length = 0;
293 }
294
295 if (ACPI_SUCCESS (status)) {
296 /*
297 * Find out how large a buffer is needed
298 * to contain the returned object
299 */
300 status = acpi_ut_get_object_size (internal_return_obj,
301 &buffer_space_needed);
302 if (ACPI_SUCCESS (status)) {
303 /* Validate/Allocate/Clear caller buffer */
304
305 status = acpi_ut_initialize_buffer (return_buffer, buffer_space_needed);
306 if (ACPI_FAILURE (status)) {
307 /*
308 * Caller's buffer is too small or a new one can't be allocated
309 */
310 ACPI_DEBUG_PRINT ((ACPI_DB_INFO,
311 "Needed buffer size %X, %s\n",
312 (u32) buffer_space_needed, acpi_format_exception (status)));
313 }
314 else {
315 /*
316 * We have enough space for the object, build it
317 */
318 status = acpi_ut_copy_iobject_to_eobject (internal_return_obj,
319 return_buffer);
320 }
321 }
322 }
323 }
324 }
325
326 if (internal_return_obj) {
327 /*
328 * Delete the internal return object. NOTE: Interpreter
329 * must be locked to avoid race condition.
330 */
331 status2 = acpi_ex_enter_interpreter ();
332 if (ACPI_SUCCESS (status2)) {
333 /*
334 * Delete the internal return object. (Or at least
335 * decrement the reference count by one)
336 */
337 acpi_ut_remove_reference (internal_return_obj);
338 acpi_ex_exit_interpreter ();
339 }
340 }
341
342 /*
343 * Free the input parameter list (if we created one),
344 */
345 if (internal_params) {
346 /* Free the allocated parameter block */
347
348 acpi_ut_delete_internal_object_list (internal_params);
349 }
350
351 return_ACPI_STATUS (status);
352 }
353
354
355 /*******************************************************************************
356 *
357 * FUNCTION: acpi_walk_namespace
358 *
359 * PARAMETERS: Type - acpi_object_type to search for
360 * start_object - Handle in namespace where search begins
361 * max_depth - Depth to which search is to reach
362 * user_function - Called when an object of "Type" is found
363 * Context - Passed to user function
364 * return_value - Location where return value of
365 * user_function is put if terminated early
366 *
367 * RETURNS Return value from the user_function if terminated early.
368 * Otherwise, returns NULL.
369 *
370 * DESCRIPTION: Performs a modified depth-first walk of the namespace tree,
371 * starting (and ending) at the object specified by start_handle.
372 * The user_function is called whenever an object that matches
373 * the type parameter is found. If the user function returns
374 * a non-zero value, the search is terminated immediately and this
375 * value is returned to the caller.
376 *
377 * The point of this procedure is to provide a generic namespace
378 * walk routine that can be called from multiple places to
379 * provide multiple services; the User Function can be tailored
380 * to each task, whether it is a print function, a compare
381 * function, etc.
382 *
383 ******************************************************************************/
384
385 acpi_status
acpi_walk_namespace(acpi_object_type type,acpi_handle start_object,u32 max_depth,acpi_walk_callback user_function,void * context,void ** return_value)386 acpi_walk_namespace (
387 acpi_object_type type,
388 acpi_handle start_object,
389 u32 max_depth,
390 acpi_walk_callback user_function,
391 void *context,
392 void **return_value)
393 {
394 acpi_status status;
395
396
397 ACPI_FUNCTION_TRACE ("acpi_walk_namespace");
398
399
400 /* Parameter validation */
401
402 if ((type > ACPI_TYPE_EXTERNAL_MAX) ||
403 (!max_depth) ||
404 (!user_function)) {
405 return_ACPI_STATUS (AE_BAD_PARAMETER);
406 }
407
408 /*
409 * Lock the namespace around the walk.
410 * The namespace will be unlocked/locked around each call
411 * to the user function - since this function
412 * must be allowed to make Acpi calls itself.
413 */
414 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
415 if (ACPI_FAILURE (status)) {
416 return_ACPI_STATUS (status);
417 }
418
419 status = acpi_ns_walk_namespace (type, start_object, max_depth, ACPI_NS_WALK_UNLOCK,
420 user_function, context, return_value);
421
422 (void) acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
423 return_ACPI_STATUS (status);
424 }
425
426
427 /*******************************************************************************
428 *
429 * FUNCTION: acpi_ns_get_device_callback
430 *
431 * PARAMETERS: Callback from acpi_get_device
432 *
433 * RETURN: Status
434 *
435 * DESCRIPTION: Takes callbacks from walk_namespace and filters out all non-
436 * present devices, or if they specified a HID, it filters based
437 * on that.
438 *
439 ******************************************************************************/
440
441 static acpi_status
acpi_ns_get_device_callback(acpi_handle obj_handle,u32 nesting_level,void * context,void ** return_value)442 acpi_ns_get_device_callback (
443 acpi_handle obj_handle,
444 u32 nesting_level,
445 void *context,
446 void **return_value)
447 {
448 struct acpi_get_devices_info *info = context;
449 acpi_status status;
450 struct acpi_namespace_node *node;
451 u32 flags;
452 struct acpi_device_id hid;
453 struct acpi_compatible_id_list *cid;
454 acpi_native_uint i;
455
456
457 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
458 if (ACPI_FAILURE (status)) {
459 return (status);
460 }
461
462 node = acpi_ns_map_handle_to_node (obj_handle);
463 status = acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
464 if (ACPI_FAILURE (status)) {
465 return (status);
466 }
467
468 if (!node) {
469 return (AE_BAD_PARAMETER);
470 }
471
472 /* Run _STA to determine if device is present */
473
474 status = acpi_ut_execute_STA (node, &flags);
475 if (ACPI_FAILURE (status)) {
476 return (AE_CTRL_DEPTH);
477 }
478
479 if (!(flags & 0x01)) {
480 /* Don't return at the device or children of the device if not there */
481
482 return (AE_CTRL_DEPTH);
483 }
484
485 /* Filter based on device HID & CID */
486
487 if (info->hid != NULL) {
488 status = acpi_ut_execute_HID (node, &hid);
489 if (status == AE_NOT_FOUND) {
490 return (AE_OK);
491 }
492 else if (ACPI_FAILURE (status)) {
493 return (AE_CTRL_DEPTH);
494 }
495
496 if (ACPI_STRNCMP (hid.value, info->hid, sizeof (hid.value)) != 0) {
497 /* Get the list of Compatible IDs */
498
499 status = acpi_ut_execute_CID (node, &cid);
500 if (status == AE_NOT_FOUND) {
501 return (AE_OK);
502 }
503 else if (ACPI_FAILURE (status)) {
504 return (AE_CTRL_DEPTH);
505 }
506
507 /* Walk the CID list */
508
509 for (i = 0; i < cid->count; i++) {
510 if (ACPI_STRNCMP (cid->id[i].value, info->hid,
511 sizeof (struct acpi_compatible_id)) != 0) {
512 ACPI_MEM_FREE (cid);
513 return (AE_OK);
514 }
515 }
516 ACPI_MEM_FREE (cid);
517 }
518 }
519
520 status = info->user_function (obj_handle, nesting_level, info->context, return_value);
521 return (status);
522 }
523
524
525 /*******************************************************************************
526 *
527 * FUNCTION: acpi_get_devices
528 *
529 * PARAMETERS: HID - HID to search for. Can be NULL.
530 * user_function - Called when a matching object is found
531 * Context - Passed to user function
532 * return_value - Location where return value of
533 * user_function is put if terminated early
534 *
535 * RETURNS Return value from the user_function if terminated early.
536 * Otherwise, returns NULL.
537 *
538 * DESCRIPTION: Performs a modified depth-first walk of the namespace tree,
539 * starting (and ending) at the object specified by start_handle.
540 * The user_function is called whenever an object of type
541 * Device is found. If the user function returns
542 * a non-zero value, the search is terminated immediately and this
543 * value is returned to the caller.
544 *
545 * This is a wrapper for walk_namespace, but the callback performs
546 * additional filtering. Please see acpi_get_device_callback.
547 *
548 ******************************************************************************/
549
550 acpi_status
acpi_get_devices(char * HID,acpi_walk_callback user_function,void * context,void ** return_value)551 acpi_get_devices (
552 char *HID,
553 acpi_walk_callback user_function,
554 void *context,
555 void **return_value)
556 {
557 acpi_status status;
558 struct acpi_get_devices_info info;
559
560
561 ACPI_FUNCTION_TRACE ("acpi_get_devices");
562
563
564 /* Parameter validation */
565
566 if (!user_function) {
567 return_ACPI_STATUS (AE_BAD_PARAMETER);
568 }
569
570 /*
571 * We're going to call their callback from OUR callback, so we need
572 * to know what it is, and their context parameter.
573 */
574 info.context = context;
575 info.user_function = user_function;
576 info.hid = HID;
577
578 /*
579 * Lock the namespace around the walk.
580 * The namespace will be unlocked/locked around each call
581 * to the user function - since this function
582 * must be allowed to make Acpi calls itself.
583 */
584 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
585 if (ACPI_FAILURE (status)) {
586 return_ACPI_STATUS (status);
587 }
588
589 status = acpi_ns_walk_namespace (ACPI_TYPE_DEVICE,
590 ACPI_ROOT_OBJECT, ACPI_UINT32_MAX,
591 ACPI_NS_WALK_UNLOCK,
592 acpi_ns_get_device_callback, &info,
593 return_value);
594
595 (void) acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
596 return_ACPI_STATUS (status);
597 }
598
599
600 /*******************************************************************************
601 *
602 * FUNCTION: acpi_attach_data
603 *
604 * PARAMETERS: obj_handle - Namespace node
605 * Handler - Handler for this attachment
606 * Data - Pointer to data to be attached
607 *
608 * RETURN: Status
609 *
610 * DESCRIPTION: Attach arbitrary data and handler to a namespace node.
611 *
612 ******************************************************************************/
613
614 acpi_status
acpi_attach_data(acpi_handle obj_handle,acpi_object_handler handler,void * data)615 acpi_attach_data (
616 acpi_handle obj_handle,
617 acpi_object_handler handler,
618 void *data)
619 {
620 struct acpi_namespace_node *node;
621 acpi_status status;
622
623
624 /* Parameter validation */
625
626 if (!obj_handle ||
627 !handler ||
628 !data) {
629 return (AE_BAD_PARAMETER);
630 }
631
632 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
633 if (ACPI_FAILURE (status)) {
634 return (status);
635 }
636
637 /* Convert and validate the handle */
638
639 node = acpi_ns_map_handle_to_node (obj_handle);
640 if (!node) {
641 status = AE_BAD_PARAMETER;
642 goto unlock_and_exit;
643 }
644
645 status = acpi_ns_attach_data (node, handler, data);
646
647 unlock_and_exit:
648 (void) acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
649 return (status);
650 }
651
652
653 /*******************************************************************************
654 *
655 * FUNCTION: acpi_detach_data
656 *
657 * PARAMETERS: obj_handle - Namespace node handle
658 * Handler - Handler used in call to acpi_attach_data
659 *
660 * RETURN: Status
661 *
662 * DESCRIPTION: Remove data that was previously attached to a node.
663 *
664 ******************************************************************************/
665
666 acpi_status
acpi_detach_data(acpi_handle obj_handle,acpi_object_handler handler)667 acpi_detach_data (
668 acpi_handle obj_handle,
669 acpi_object_handler handler)
670 {
671 struct acpi_namespace_node *node;
672 acpi_status status;
673
674
675 /* Parameter validation */
676
677 if (!obj_handle ||
678 !handler) {
679 return (AE_BAD_PARAMETER);
680 }
681
682 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
683 if (ACPI_FAILURE (status)) {
684 return (status);
685 }
686
687 /* Convert and validate the handle */
688
689 node = acpi_ns_map_handle_to_node (obj_handle);
690 if (!node) {
691 status = AE_BAD_PARAMETER;
692 goto unlock_and_exit;
693 }
694
695 status = acpi_ns_detach_data (node, handler);
696
697 unlock_and_exit:
698 (void) acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
699 return (status);
700 }
701
702
703 /*******************************************************************************
704 *
705 * FUNCTION: acpi_get_data
706 *
707 * PARAMETERS: obj_handle - Namespace node
708 * Handler - Handler used in call to attach_data
709 * Data - Where the data is returned
710 *
711 * RETURN: Status
712 *
713 * DESCRIPTION: Retrieve data that was previously attached to a namespace node.
714 *
715 ******************************************************************************/
716
717 acpi_status
acpi_get_data(acpi_handle obj_handle,acpi_object_handler handler,void ** data)718 acpi_get_data (
719 acpi_handle obj_handle,
720 acpi_object_handler handler,
721 void **data)
722 {
723 struct acpi_namespace_node *node;
724 acpi_status status;
725
726
727 /* Parameter validation */
728
729 if (!obj_handle ||
730 !handler ||
731 !data) {
732 return (AE_BAD_PARAMETER);
733 }
734
735 status = acpi_ut_acquire_mutex (ACPI_MTX_NAMESPACE);
736 if (ACPI_FAILURE (status)) {
737 return (status);
738 }
739
740 /* Convert and validate the handle */
741
742 node = acpi_ns_map_handle_to_node (obj_handle);
743 if (!node) {
744 status = AE_BAD_PARAMETER;
745 goto unlock_and_exit;
746 }
747
748 status = acpi_ns_get_attached_data (node, handler, data);
749
750 unlock_and_exit:
751 (void) acpi_ut_release_mutex (ACPI_MTX_NAMESPACE);
752 return (status);
753 }
754
755
756