1// SPDX-License-Identifier: GPL-2.0+
2// Copyright (c) 2016-2017 Hisilicon Limited.
3
4#include "hclge_main.h"
5#include "hclge_dcb.h"
6#include "hclge_tm.h"
7#include "hnae3.h"
8
9#define BW_PERCENT 100
10
11static int hclge_ieee_ets_to_tm_info(struct hclge_dev *hdev,
12 struct ieee_ets *ets)
13{
14 u8 i;
15
16 for (i = 0; i < HNAE3_MAX_TC; i++) {
17 switch (ets->tc_tsa[i]) {
18 case IEEE_8021QAZ_TSA_STRICT:
19 hdev->tm_info.tc_info[i].tc_sch_mode =
20 HCLGE_SCH_MODE_SP;
21 hdev->tm_info.pg_info[0].tc_dwrr[i] = 0;
22 break;
23 case IEEE_8021QAZ_TSA_ETS:
24 hdev->tm_info.tc_info[i].tc_sch_mode =
25 HCLGE_SCH_MODE_DWRR;
26 hdev->tm_info.pg_info[0].tc_dwrr[i] =
27 ets->tc_tx_bw[i];
28 break;
29 default:
30 /* Hardware only supports SP (strict priority)
31 * or ETS (enhanced transmission selection)
32 * algorithms, if we receive some other value
33 * from dcbnl, then throw an error.
34 */
35 return -EINVAL;
36 }
37 }
38
39 hclge_tm_prio_tc_info_update(hdev, prio_tc: ets->prio_tc);
40
41 return 0;
42}
43
44static void hclge_tm_info_to_ieee_ets(struct hclge_dev *hdev,
45 struct ieee_ets *ets)
46{
47 u32 i;
48
49 memset(ets, 0, sizeof(*ets));
50 ets->willing = 1;
51 ets->ets_cap = hdev->tc_max;
52
53 for (i = 0; i < HNAE3_MAX_TC; i++) {
54 ets->prio_tc[i] = hdev->tm_info.prio_tc[i];
55 if (i < hdev->tm_info.num_tc)
56 ets->tc_tx_bw[i] = hdev->tm_info.pg_info[0].tc_dwrr[i];
57 else
58 ets->tc_tx_bw[i] = 0;
59
60 if (hdev->tm_info.tc_info[i].tc_sch_mode ==
61 HCLGE_SCH_MODE_SP)
62 ets->tc_tsa[i] = IEEE_8021QAZ_TSA_STRICT;
63 else
64 ets->tc_tsa[i] = IEEE_8021QAZ_TSA_ETS;
65 }
66}
67
68/* IEEE std */
69static int hclge_ieee_getets(struct hnae3_handle *h, struct ieee_ets *ets)
70{
71 struct hclge_vport *vport = hclge_get_vport(handle: h);
72 struct hclge_dev *hdev = vport->back;
73
74 hclge_tm_info_to_ieee_ets(hdev, ets);
75
76 return 0;
77}
78
79static int hclge_dcb_common_validate(struct hclge_dev *hdev, u8 num_tc,
80 u8 *prio_tc)
81{
82 int i;
83
84 if (num_tc > hdev->tc_max) {
85 dev_err(&hdev->pdev->dev,
86 "tc num checking failed, %u > tc_max(%u)\n",
87 num_tc, hdev->tc_max);
88 return -EINVAL;
89 }
90
91 for (i = 0; i < HNAE3_MAX_USER_PRIO; i++) {
92 if (prio_tc[i] >= num_tc) {
93 dev_err(&hdev->pdev->dev,
94 "prio_tc[%d] checking failed, %u >= num_tc(%u)\n",
95 i, prio_tc[i], num_tc);
96 return -EINVAL;
97 }
98 }
99
100 if (num_tc > hdev->vport[0].alloc_tqps) {
101 dev_err(&hdev->pdev->dev,
102 "allocated tqp checking failed, %u > tqp(%u)\n",
103 num_tc, hdev->vport[0].alloc_tqps);
104 return -EINVAL;
105 }
106
107 return 0;
108}
109
110static u8 hclge_ets_tc_changed(struct hclge_dev *hdev, struct ieee_ets *ets,
111 bool *changed)
112{
113 u8 max_tc_id = 0;
114 u8 i;
115
116 for (i = 0; i < HNAE3_MAX_USER_PRIO; i++) {
117 if (ets->prio_tc[i] != hdev->tm_info.prio_tc[i])
118 *changed = true;
119
120 if (ets->prio_tc[i] > max_tc_id)
121 max_tc_id = ets->prio_tc[i];
122 }
123
124 /* return max tc number, max tc id need to plus 1 */
125 return max_tc_id + 1;
126}
127
128static int hclge_ets_sch_mode_validate(struct hclge_dev *hdev,
129 struct ieee_ets *ets, bool *changed,
130 u8 tc_num)
131{
132 bool has_ets_tc = false;
133 u32 total_ets_bw = 0;
134 u8 i;
135
136 for (i = 0; i < HNAE3_MAX_TC; i++) {
137 switch (ets->tc_tsa[i]) {
138 case IEEE_8021QAZ_TSA_STRICT:
139 if (hdev->tm_info.tc_info[i].tc_sch_mode !=
140 HCLGE_SCH_MODE_SP)
141 *changed = true;
142 break;
143 case IEEE_8021QAZ_TSA_ETS:
144 if (i >= tc_num) {
145 dev_err(&hdev->pdev->dev,
146 "tc%u is disabled, cannot set ets bw\n",
147 i);
148 return -EINVAL;
149 }
150
151 /* The hardware will switch to sp mode if bandwidth is
152 * 0, so limit ets bandwidth must be greater than 0.
153 */
154 if (!ets->tc_tx_bw[i]) {
155 dev_err(&hdev->pdev->dev,
156 "tc%u ets bw cannot be 0\n", i);
157 return -EINVAL;
158 }
159
160 if (hdev->tm_info.tc_info[i].tc_sch_mode !=
161 HCLGE_SCH_MODE_DWRR)
162 *changed = true;
163
164 total_ets_bw += ets->tc_tx_bw[i];
165 has_ets_tc = true;
166 break;
167 default:
168 return -EINVAL;
169 }
170 }
171
172 if (has_ets_tc && total_ets_bw != BW_PERCENT)
173 return -EINVAL;
174
175 return 0;
176}
177
178static int hclge_ets_validate(struct hclge_dev *hdev, struct ieee_ets *ets,
179 u8 *tc, bool *changed)
180{
181 u8 tc_num;
182 int ret;
183
184 tc_num = hclge_ets_tc_changed(hdev, ets, changed);
185
186 ret = hclge_dcb_common_validate(hdev, num_tc: tc_num, prio_tc: ets->prio_tc);
187 if (ret)
188 return ret;
189
190 ret = hclge_ets_sch_mode_validate(hdev, ets, changed, tc_num);
191 if (ret)
192 return ret;
193
194 *tc = tc_num;
195 if (*tc != hdev->tm_info.num_tc)
196 *changed = true;
197
198 return 0;
199}
200
201static int hclge_map_update(struct hclge_dev *hdev)
202{
203 int ret;
204
205 ret = hclge_tm_schd_setup_hw(hdev);
206 if (ret)
207 return ret;
208
209 ret = hclge_pause_setup_hw(hdev, init: false);
210 if (ret)
211 return ret;
212
213 ret = hclge_buffer_alloc(hdev);
214 if (ret)
215 return ret;
216
217 hclge_comm_rss_indir_init_cfg(ae_dev: hdev->ae_dev, rss_cfg: &hdev->rss_cfg);
218
219 return hclge_rss_init_hw(hdev);
220}
221
222static int hclge_notify_down_uinit(struct hclge_dev *hdev)
223{
224 int ret;
225
226 ret = hclge_notify_client(hdev, type: HNAE3_DOWN_CLIENT);
227 if (ret)
228 return ret;
229
230 ret = hclge_tm_flush_cfg(hdev, enable: true);
231 if (ret)
232 return ret;
233
234 return hclge_notify_client(hdev, type: HNAE3_UNINIT_CLIENT);
235}
236
237static int hclge_notify_init_up(struct hclge_dev *hdev)
238{
239 int ret;
240
241 ret = hclge_notify_client(hdev, type: HNAE3_INIT_CLIENT);
242 if (ret)
243 return ret;
244
245 ret = hclge_tm_flush_cfg(hdev, enable: false);
246 if (ret)
247 return ret;
248
249 return hclge_notify_client(hdev, type: HNAE3_UP_CLIENT);
250}
251
252static int hclge_ieee_setets(struct hnae3_handle *h, struct ieee_ets *ets)
253{
254 struct hclge_vport *vport = hclge_get_vport(handle: h);
255 struct net_device *netdev = h->kinfo.netdev;
256 struct hclge_dev *hdev = vport->back;
257 bool map_changed = false;
258 u8 num_tc = 0;
259 int ret;
260
261 if (!(hdev->dcbx_cap & DCB_CAP_DCBX_VER_IEEE) ||
262 h->kinfo.tc_info.mqprio_active)
263 return -EINVAL;
264
265 ret = hclge_ets_validate(hdev, ets, tc: &num_tc, changed: &map_changed);
266 if (ret)
267 return ret;
268
269 if (map_changed) {
270 netif_dbg(h, drv, netdev, "set ets\n");
271
272 ret = hclge_notify_down_uinit(hdev);
273 if (ret)
274 return ret;
275 }
276
277 hclge_tm_schd_info_update(hdev, num_tc);
278 h->kinfo.tc_info.dcb_ets_active = num_tc > 1;
279
280 ret = hclge_ieee_ets_to_tm_info(hdev, ets);
281 if (ret)
282 goto err_out;
283
284 if (map_changed) {
285 ret = hclge_map_update(hdev);
286 if (ret)
287 goto err_out;
288
289 return hclge_notify_init_up(hdev);
290 }
291
292 return hclge_tm_dwrr_cfg(hdev);
293
294err_out:
295 if (!map_changed)
296 return ret;
297
298 hclge_notify_init_up(hdev);
299
300 return ret;
301}
302
303static int hclge_ieee_getpfc(struct hnae3_handle *h, struct ieee_pfc *pfc)
304{
305 struct hclge_vport *vport = hclge_get_vport(handle: h);
306 struct hclge_dev *hdev = vport->back;
307 int ret;
308
309 memset(pfc, 0, sizeof(*pfc));
310 pfc->pfc_cap = hdev->pfc_max;
311 pfc->pfc_en = hdev->tm_info.pfc_en;
312
313 ret = hclge_mac_update_stats(hdev);
314 if (ret) {
315 dev_err(&hdev->pdev->dev,
316 "failed to update MAC stats, ret = %d.\n", ret);
317 return ret;
318 }
319
320 hclge_pfc_tx_stats_get(hdev, stats: pfc->requests);
321 hclge_pfc_rx_stats_get(hdev, stats: pfc->indications);
322
323 return 0;
324}
325
326static int hclge_ieee_setpfc(struct hnae3_handle *h, struct ieee_pfc *pfc)
327{
328 struct hclge_vport *vport = hclge_get_vport(handle: h);
329 struct net_device *netdev = h->kinfo.netdev;
330 struct hclge_dev *hdev = vport->back;
331 u8 i, j, pfc_map, *prio_tc;
332 int last_bad_ret = 0;
333 int ret;
334
335 if (!(hdev->dcbx_cap & DCB_CAP_DCBX_VER_IEEE))
336 return -EINVAL;
337
338 if (pfc->pfc_en == hdev->tm_info.pfc_en)
339 return 0;
340
341 prio_tc = hdev->tm_info.prio_tc;
342 pfc_map = 0;
343
344 for (i = 0; i < hdev->tm_info.num_tc; i++) {
345 for (j = 0; j < HNAE3_MAX_USER_PRIO; j++) {
346 if ((prio_tc[j] == i) && (pfc->pfc_en & BIT(j))) {
347 pfc_map |= BIT(i);
348 break;
349 }
350 }
351 }
352
353 hdev->tm_info.hw_pfc_map = pfc_map;
354 hdev->tm_info.pfc_en = pfc->pfc_en;
355
356 netif_dbg(h, drv, netdev,
357 "set pfc: pfc_en=%x, pfc_map=%x, num_tc=%u\n",
358 pfc->pfc_en, pfc_map, hdev->tm_info.num_tc);
359
360 hclge_tm_pfc_info_update(hdev);
361
362 ret = hclge_pause_setup_hw(hdev, init: false);
363 if (ret)
364 return ret;
365
366 ret = hclge_notify_client(hdev, type: HNAE3_DOWN_CLIENT);
367 if (ret)
368 return ret;
369
370 ret = hclge_tm_flush_cfg(hdev, enable: true);
371 if (ret)
372 return ret;
373
374 /* No matter whether the following operations are performed
375 * successfully or not, disabling the tm flush and notify
376 * the network status to up are necessary.
377 * Do not return immediately.
378 */
379 ret = hclge_buffer_alloc(hdev);
380 if (ret)
381 last_bad_ret = ret;
382
383 ret = hclge_tm_flush_cfg(hdev, enable: false);
384 if (ret)
385 last_bad_ret = ret;
386
387 ret = hclge_notify_client(hdev, type: HNAE3_UP_CLIENT);
388 if (ret)
389 last_bad_ret = ret;
390
391 return last_bad_ret;
392}
393
394static int hclge_ieee_setapp(struct hnae3_handle *h, struct dcb_app *app)
395{
396 struct hclge_vport *vport = hclge_get_vport(handle: h);
397 struct net_device *netdev = h->kinfo.netdev;
398 struct hclge_dev *hdev = vport->back;
399 struct dcb_app old_app;
400 int ret;
401
402 if (app->selector != IEEE_8021QAZ_APP_SEL_DSCP ||
403 app->protocol >= HNAE3_MAX_DSCP ||
404 app->priority >= HNAE3_MAX_USER_PRIO)
405 return -EINVAL;
406
407 dev_info(&hdev->pdev->dev, "setapp dscp=%u priority=%u\n",
408 app->protocol, app->priority);
409
410 if (app->priority == h->kinfo.dscp_prio[app->protocol])
411 return 0;
412
413 ret = dcb_ieee_setapp(netdev, app);
414 if (ret)
415 return ret;
416
417 old_app.selector = IEEE_8021QAZ_APP_SEL_DSCP;
418 old_app.protocol = app->protocol;
419 old_app.priority = h->kinfo.dscp_prio[app->protocol];
420
421 h->kinfo.dscp_prio[app->protocol] = app->priority;
422 ret = hclge_dscp_to_tc_map(hdev);
423 if (ret) {
424 dev_err(&hdev->pdev->dev,
425 "failed to set dscp to tc map, ret = %d\n", ret);
426 h->kinfo.dscp_prio[app->protocol] = old_app.priority;
427 (void)dcb_ieee_delapp(netdev, app);
428 return ret;
429 }
430
431 vport->nic.kinfo.tc_map_mode = HNAE3_TC_MAP_MODE_DSCP;
432 if (old_app.priority == HNAE3_PRIO_ID_INVALID)
433 h->kinfo.dscp_app_cnt++;
434 else
435 ret = dcb_ieee_delapp(netdev, &old_app);
436
437 return ret;
438}
439
440static int hclge_ieee_delapp(struct hnae3_handle *h, struct dcb_app *app)
441{
442 struct hclge_vport *vport = hclge_get_vport(handle: h);
443 struct net_device *netdev = h->kinfo.netdev;
444 struct hclge_dev *hdev = vport->back;
445 int ret;
446
447 if (app->selector != IEEE_8021QAZ_APP_SEL_DSCP ||
448 app->protocol >= HNAE3_MAX_DSCP ||
449 app->priority >= HNAE3_MAX_USER_PRIO ||
450 app->priority != h->kinfo.dscp_prio[app->protocol])
451 return -EINVAL;
452
453 dev_info(&hdev->pdev->dev, "delapp dscp=%u priority=%u\n",
454 app->protocol, app->priority);
455
456 ret = dcb_ieee_delapp(netdev, app);
457 if (ret)
458 return ret;
459
460 h->kinfo.dscp_prio[app->protocol] = HNAE3_PRIO_ID_INVALID;
461 ret = hclge_dscp_to_tc_map(hdev);
462 if (ret) {
463 dev_err(&hdev->pdev->dev,
464 "failed to del dscp to tc map, ret = %d\n", ret);
465 h->kinfo.dscp_prio[app->protocol] = app->priority;
466 (void)dcb_ieee_setapp(netdev, app);
467 return ret;
468 }
469
470 if (h->kinfo.dscp_app_cnt)
471 h->kinfo.dscp_app_cnt--;
472
473 if (!h->kinfo.dscp_app_cnt) {
474 vport->nic.kinfo.tc_map_mode = HNAE3_TC_MAP_MODE_PRIO;
475 ret = hclge_up_to_tc_map(hdev);
476 }
477
478 return ret;
479}
480
481/* DCBX configuration */
482static u8 hclge_getdcbx(struct hnae3_handle *h)
483{
484 struct hclge_vport *vport = hclge_get_vport(handle: h);
485 struct hclge_dev *hdev = vport->back;
486
487 if (h->kinfo.tc_info.mqprio_active)
488 return 0;
489
490 return hdev->dcbx_cap;
491}
492
493static u8 hclge_setdcbx(struct hnae3_handle *h, u8 mode)
494{
495 struct hclge_vport *vport = hclge_get_vport(handle: h);
496 struct net_device *netdev = h->kinfo.netdev;
497 struct hclge_dev *hdev = vport->back;
498
499 netif_dbg(h, drv, netdev, "set dcbx: mode=%u\n", mode);
500
501 /* No support for LLD_MANAGED modes or CEE */
502 if ((mode & DCB_CAP_DCBX_LLD_MANAGED) ||
503 (mode & DCB_CAP_DCBX_VER_CEE) ||
504 !(mode & DCB_CAP_DCBX_HOST))
505 return 1;
506
507 hdev->dcbx_cap = mode;
508
509 return 0;
510}
511
512static int hclge_mqprio_qopt_check(struct hclge_dev *hdev,
513 struct tc_mqprio_qopt_offload *mqprio_qopt)
514{
515 u16 queue_sum = 0;
516 int ret;
517 int i;
518
519 if (!mqprio_qopt->qopt.num_tc) {
520 mqprio_qopt->qopt.num_tc = 1;
521 return 0;
522 }
523
524 ret = hclge_dcb_common_validate(hdev, num_tc: mqprio_qopt->qopt.num_tc,
525 prio_tc: mqprio_qopt->qopt.prio_tc_map);
526 if (ret)
527 return ret;
528
529 for (i = 0; i < mqprio_qopt->qopt.num_tc; i++) {
530 if (!is_power_of_2(n: mqprio_qopt->qopt.count[i])) {
531 dev_err(&hdev->pdev->dev,
532 "qopt queue count must be power of 2\n");
533 return -EINVAL;
534 }
535
536 if (mqprio_qopt->qopt.count[i] > hdev->pf_rss_size_max) {
537 dev_err(&hdev->pdev->dev,
538 "qopt queue count should be no more than %u\n",
539 hdev->pf_rss_size_max);
540 return -EINVAL;
541 }
542
543 if (mqprio_qopt->qopt.offset[i] != queue_sum) {
544 dev_err(&hdev->pdev->dev,
545 "qopt queue offset must start from 0, and being continuous\n");
546 return -EINVAL;
547 }
548
549 if (mqprio_qopt->min_rate[i] || mqprio_qopt->max_rate[i]) {
550 dev_err(&hdev->pdev->dev,
551 "qopt tx_rate is not supported\n");
552 return -EOPNOTSUPP;
553 }
554
555 queue_sum = mqprio_qopt->qopt.offset[i];
556 queue_sum += mqprio_qopt->qopt.count[i];
557 }
558 if (hdev->vport[0].alloc_tqps < queue_sum) {
559 dev_err(&hdev->pdev->dev,
560 "qopt queue count sum should be less than %u\n",
561 hdev->vport[0].alloc_tqps);
562 return -EINVAL;
563 }
564
565 return 0;
566}
567
568static void hclge_sync_mqprio_qopt(struct hnae3_tc_info *tc_info,
569 struct tc_mqprio_qopt_offload *mqprio_qopt)
570{
571 memset(tc_info, 0, sizeof(*tc_info));
572 tc_info->num_tc = mqprio_qopt->qopt.num_tc;
573 memcpy(tc_info->prio_tc, mqprio_qopt->qopt.prio_tc_map,
574 sizeof_field(struct hnae3_tc_info, prio_tc));
575 memcpy(tc_info->tqp_count, mqprio_qopt->qopt.count,
576 sizeof_field(struct hnae3_tc_info, tqp_count));
577 memcpy(tc_info->tqp_offset, mqprio_qopt->qopt.offset,
578 sizeof_field(struct hnae3_tc_info, tqp_offset));
579}
580
581static int hclge_config_tc(struct hclge_dev *hdev,
582 struct hnae3_tc_info *tc_info)
583{
584 int i;
585
586 hclge_tm_schd_info_update(hdev, num_tc: tc_info->num_tc);
587 for (i = 0; i < HNAE3_MAX_USER_PRIO; i++)
588 hdev->tm_info.prio_tc[i] = tc_info->prio_tc[i];
589
590 return hclge_map_update(hdev);
591}
592
593/* Set up TC for hardware offloaded mqprio in channel mode */
594static int hclge_setup_tc(struct hnae3_handle *h,
595 struct tc_mqprio_qopt_offload *mqprio_qopt)
596{
597 struct hclge_vport *vport = hclge_get_vport(handle: h);
598 struct hnae3_knic_private_info *kinfo;
599 struct hclge_dev *hdev = vport->back;
600 struct hnae3_tc_info old_tc_info;
601 u8 tc = mqprio_qopt->qopt.num_tc;
602 int ret;
603
604 /* if client unregistered, it's not allowed to change
605 * mqprio configuration, which may cause uninit ring
606 * fail.
607 */
608 if (!test_bit(HCLGE_STATE_NIC_REGISTERED, &hdev->state))
609 return -EBUSY;
610
611 kinfo = &vport->nic.kinfo;
612 if (kinfo->tc_info.dcb_ets_active)
613 return -EINVAL;
614
615 ret = hclge_mqprio_qopt_check(hdev, mqprio_qopt);
616 if (ret) {
617 dev_err(&hdev->pdev->dev,
618 "failed to check mqprio qopt params, ret = %d\n", ret);
619 return ret;
620 }
621
622 kinfo->tc_info.mqprio_destroy = !tc;
623
624 ret = hclge_notify_down_uinit(hdev);
625 if (ret)
626 return ret;
627
628 memcpy(&old_tc_info, &kinfo->tc_info, sizeof(old_tc_info));
629 hclge_sync_mqprio_qopt(tc_info: &kinfo->tc_info, mqprio_qopt);
630 kinfo->tc_info.mqprio_active = tc > 0;
631
632 ret = hclge_config_tc(hdev, tc_info: &kinfo->tc_info);
633 if (ret)
634 goto err_out;
635
636 return hclge_notify_init_up(hdev);
637
638err_out:
639 if (!tc) {
640 dev_warn(&hdev->pdev->dev,
641 "failed to destroy mqprio, will active after reset, ret = %d\n",
642 ret);
643 } else {
644 /* roll-back */
645 memcpy(&kinfo->tc_info, &old_tc_info, sizeof(old_tc_info));
646 if (hclge_config_tc(hdev, tc_info: &kinfo->tc_info))
647 dev_err(&hdev->pdev->dev,
648 "failed to roll back tc configuration\n");
649 }
650 hclge_notify_init_up(hdev);
651
652 return ret;
653}
654
655static const struct hnae3_dcb_ops hns3_dcb_ops = {
656 .ieee_getets = hclge_ieee_getets,
657 .ieee_setets = hclge_ieee_setets,
658 .ieee_getpfc = hclge_ieee_getpfc,
659 .ieee_setpfc = hclge_ieee_setpfc,
660 .ieee_setapp = hclge_ieee_setapp,
661 .ieee_delapp = hclge_ieee_delapp,
662 .getdcbx = hclge_getdcbx,
663 .setdcbx = hclge_setdcbx,
664 .setup_tc = hclge_setup_tc,
665};
666
667void hclge_dcb_ops_set(struct hclge_dev *hdev)
668{
669 struct hclge_vport *vport = hdev->vport;
670 struct hnae3_knic_private_info *kinfo;
671
672 /* Hdev does not support DCB or vport is
673 * not a pf, then dcb_ops is not set.
674 */
675 if (!hnae3_dev_dcb_supported(hdev) ||
676 vport->vport_id != 0)
677 return;
678
679 kinfo = &vport->nic.kinfo;
680 kinfo->dcb_ops = &hns3_dcb_ops;
681 hdev->dcbx_cap = DCB_CAP_DCBX_VER_IEEE | DCB_CAP_DCBX_HOST;
682}
683

source code of linux/drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_dcb.c