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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * DisplayPort CEC-Tunneling-over-AUX support
4 *
5 * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
6 */
7
8#include <linux/kernel.h>
9#include <linux/module.h>
10#include <linux/slab.h>
11
12#include <media/cec.h>
13
14#include <drm/drm_connector.h>
15#include <drm/drm_device.h>
16#include <drm/drm_dp_helper.h>
17
18/*
19 * Unfortunately it turns out that we have a chicken-and-egg situation
20 * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
21 * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
22 * Parade PS176), but they do not wire up the CEC pin, thus making CEC
23 * useless. Note that MegaChips 2900-based adapters appear to have good
24 * support for CEC tunneling. Those adapters that I have tested using
25 * this chipset all have the CEC line connected.
26 *
27 * Sadly there is no way for this driver to know this. What happens is
28 * that a /dev/cecX device is created that is isolated and unable to see
29 * any of the other CEC devices. Quite literally the CEC wire is cut
30 * (or in this case, never connected in the first place).
31 *
32 * The reason so few adapters support this is that this tunneling protocol
33 * was never supported by any OS. So there was no easy way of testing it,
34 * and no incentive to correctly wire up the CEC pin.
35 *
36 * Hopefully by creating this driver it will be easier for vendors to
37 * finally fix their adapters and test the CEC functionality.
38 *
39 * I keep a list of known working adapters here:
40 *
41 * https://hverkuil.home.xs4all.nl/cec-status.txt
42 *
43 * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
44 * and is not yet listed there.
45 *
46 * Note that the current implementation does not support CEC over an MST hub.
47 * As far as I can see there is no mechanism defined in the DisplayPort
48 * standard to transport CEC interrupts over an MST device. It might be
49 * possible to do this through polling, but I have not been able to get that
50 * to work.
51 */
52
53/**
54 * DOC: dp cec helpers
55 *
56 * These functions take care of supporting the CEC-Tunneling-over-AUX
57 * feature of DisplayPort-to-HDMI adapters.
58 */
59
60/*
61 * When the EDID is unset because the HPD went low, then the CEC DPCD registers
62 * typically can no longer be read (true for a DP-to-HDMI adapter since it is
63 * powered by the HPD). However, some displays toggle the HPD off and on for a
64 * short period for one reason or another, and that would cause the CEC adapter
65 * to be removed and added again, even though nothing else changed.
66 *
67 * This module parameter sets a delay in seconds before the CEC adapter is
68 * actually unregistered. Only if the HPD does not return within that time will
69 * the CEC adapter be unregistered.
70 *
71 * If it is set to a value >= NEVER_UNREG_DELAY, then the CEC adapter will never
72 * be unregistered for as long as the connector remains registered.
73 *
74 * If it is set to 0, then the CEC adapter will be unregistered immediately as
75 * soon as the HPD disappears.
76 *
77 * The default is one second to prevent short HPD glitches from unregistering
78 * the CEC adapter.
79 *
80 * Note that for integrated HDMI branch devices that support CEC the DPCD
81 * registers remain available even if the HPD goes low since it is not powered
82 * by the HPD. In that case the CEC adapter will never be unregistered during
83 * the life time of the connector. At least, this is the theory since I do not
84 * have hardware with an integrated HDMI branch device that supports CEC.
85 */
86#define NEVER_UNREG_DELAY 1000
87static unsigned int drm_dp_cec_unregister_delay = 1;
88module_param(drm_dp_cec_unregister_delay, uint, 0600);
89MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
90 "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");
91
92static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
93{
94 struct drm_dp_aux *aux = cec_get_drvdata(adap);
95 u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
96 ssize_t err = 0;
97
98 err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
99 return (enable && err < 0) ? err : 0;
100}
101
102static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
103{
104 struct drm_dp_aux *aux = cec_get_drvdata(adap);
105 /* Bit 15 (logical address 15) should always be set */
106 u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
107 u8 mask[2];
108 ssize_t err;
109
110 if (addr != CEC_LOG_ADDR_INVALID)
111 la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
112 mask[0] = la_mask & 0xff;
113 mask[1] = la_mask >> 8;
114 err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
115 return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
116}
117
118static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
119 u32 signal_free_time, struct cec_msg *msg)
120{
121 struct drm_dp_aux *aux = cec_get_drvdata(adap);
122 unsigned int retries = min(5, attempts - 1);
123 ssize_t err;
124
125 err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
126 msg->msg, msg->len);
127 if (err < 0)
128 return err;
129
130 err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
131 (msg->len - 1) | (retries << 4) |
132 DP_CEC_TX_MESSAGE_SEND);
133 return err < 0 ? err : 0;
134}
135
136static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
137 bool enable)
138{
139 struct drm_dp_aux *aux = cec_get_drvdata(adap);
140 ssize_t err;
141 u8 val;
142
143 if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
144 return 0;
145
146 err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
147 if (err >= 0) {
148 if (enable)
149 val |= DP_CEC_SNOOPING_ENABLE;
150 else
151 val &= ~DP_CEC_SNOOPING_ENABLE;
152 err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
153 }
154 return (enable && err < 0) ? err : 0;
155}
156
157static void drm_dp_cec_adap_status(struct cec_adapter *adap,
158 struct seq_file *file)
159{
160 struct drm_dp_aux *aux = cec_get_drvdata(adap);
161 struct drm_dp_desc desc;
162 struct drm_dp_dpcd_ident *id = &desc.ident;
163
164 if (drm_dp_read_desc(aux, &desc, true))
165 return;
166 seq_printf(file, "OUI: %*phD\n",
167 (int)sizeof(id->oui), id->oui);
168 seq_printf(file, "ID: %*pE\n",
169 (int)strnlen(id->device_id, sizeof(id->device_id)),
170 id->device_id);
171 seq_printf(file, "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
172 /*
173 * Show this both in decimal and hex: at least one vendor
174 * always reports this in hex.
175 */
176 seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
177 id->sw_major_rev, id->sw_minor_rev,
178 id->sw_major_rev, id->sw_minor_rev);
179}
180
181static const struct cec_adap_ops drm_dp_cec_adap_ops = {
182 .adap_enable = drm_dp_cec_adap_enable,
183 .adap_log_addr = drm_dp_cec_adap_log_addr,
184 .adap_transmit = drm_dp_cec_adap_transmit,
185 .adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
186 .adap_status = drm_dp_cec_adap_status,
187};
188
189static int drm_dp_cec_received(struct drm_dp_aux *aux)
190{
191 struct cec_adapter *adap = aux->cec.adap;
192 struct cec_msg msg;
193 u8 rx_msg_info;
194 ssize_t err;
195
196 err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
197 if (err < 0)
198 return err;
199
200 if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
201 return 0;
202
203 msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
204 err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
205 if (err < 0)
206 return err;
207
208 cec_received_msg(adap, &msg);
209 return 0;
210}
211
212static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
213{
214 struct cec_adapter *adap = aux->cec.adap;
215 u8 flags;
216
217 if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags) < 0)
218 return;
219
220 if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
221 drm_dp_cec_received(aux);
222
223 if (flags & DP_CEC_TX_MESSAGE_SENT)
224 cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
225 else if (flags & DP_CEC_TX_LINE_ERROR)
226 cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
227 CEC_TX_STATUS_MAX_RETRIES);
228 else if (flags &
229 (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
230 cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
231 CEC_TX_STATUS_MAX_RETRIES);
232 drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
233}
234
235/**
236 * drm_dp_cec_irq() - handle CEC interrupt, if any
237 * @aux: DisplayPort AUX channel
238 *
239 * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
240 * is present, then it will check for a CEC_IRQ and handle it accordingly.
241 */
242void drm_dp_cec_irq(struct drm_dp_aux *aux)
243{
244 u8 cec_irq;
245 int ret;
246
247 /* No transfer function was set, so not a DP connector */
248 if (!aux->transfer)
249 return;
250
251 mutex_lock(&aux->cec.lock);
252 if (!aux->cec.adap)
253 goto unlock;
254
255 ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
256 &cec_irq);
257 if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
258 goto unlock;
259
260 drm_dp_cec_handle_irq(aux);
261 drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
262unlock:
263 mutex_unlock(&aux->cec.lock);
264}
265EXPORT_SYMBOL(drm_dp_cec_irq);
266
267static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
268{
269 u8 cap = 0;
270
271 if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
272 !(cap & DP_CEC_TUNNELING_CAPABLE))
273 return false;
274 if (cec_cap)
275 *cec_cap = cap;
276 return true;
277}
278
279/*
280 * Called if the HPD was low for more than drm_dp_cec_unregister_delay
281 * seconds. This unregisters the CEC adapter.
282 */
283static void drm_dp_cec_unregister_work(struct work_struct *work)
284{
285 struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
286 cec.unregister_work.work);
287
288 mutex_lock(&aux->cec.lock);
289 cec_unregister_adapter(aux->cec.adap);
290 aux->cec.adap = NULL;
291 mutex_unlock(&aux->cec.lock);
292}
293
294/*
295 * A new EDID is set. If there is no CEC adapter, then create one. If
296 * there was a CEC adapter, then check if the CEC adapter properties
297 * were unchanged and just update the CEC physical address. Otherwise
298 * unregister the old CEC adapter and create a new one.
299 */
300void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
301{
302 struct drm_connector *connector = aux->cec.connector;
303 u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD |
304 CEC_CAP_CONNECTOR_INFO;
305 struct cec_connector_info conn_info;
306 unsigned int num_las = 1;
307 u8 cap;
308
309 /* No transfer function was set, so not a DP connector */
310 if (!aux->transfer)
311 return;
312
313#ifndef CONFIG_MEDIA_CEC_RC
314 /*
315 * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
316 * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
317 *
318 * Do this here as well to ensure the tests against cec_caps are
319 * correct.
320 */
321 cec_caps &= ~CEC_CAP_RC;
322#endif
323 cancel_delayed_work_sync(&aux->cec.unregister_work);
324
325 mutex_lock(&aux->cec.lock);
326 if (!drm_dp_cec_cap(aux, &cap)) {
327 /* CEC is not supported, unregister any existing adapter */
328 cec_unregister_adapter(aux->cec.adap);
329 aux->cec.adap = NULL;
330 goto unlock;
331 }
332
333 if (cap & DP_CEC_SNOOPING_CAPABLE)
334 cec_caps |= CEC_CAP_MONITOR_ALL;
335 if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
336 num_las = CEC_MAX_LOG_ADDRS;
337
338 if (aux->cec.adap) {
339 if (aux->cec.adap->capabilities == cec_caps &&
340 aux->cec.adap->available_log_addrs == num_las) {
341 /* Unchanged, so just set the phys addr */
342 cec_s_phys_addr_from_edid(aux->cec.adap, edid);
343 goto unlock;
344 }
345 /*
346 * The capabilities changed, so unregister the old
347 * adapter first.
348 */
349 cec_unregister_adapter(aux->cec.adap);
350 }
351
352 /* Create a new adapter */
353 aux->cec.adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
354 aux, connector->name, cec_caps,
355 num_las);
356 if (IS_ERR(aux->cec.adap)) {
357 aux->cec.adap = NULL;
358 goto unlock;
359 }
360
361 cec_fill_conn_info_from_drm(&conn_info, connector);
362 cec_s_conn_info(aux->cec.adap, &conn_info);
363
364 if (cec_register_adapter(aux->cec.adap, connector->dev->dev)) {
365 cec_delete_adapter(aux->cec.adap);
366 aux->cec.adap = NULL;
367 } else {
368 /*
369 * Update the phys addr for the new CEC adapter. When called
370 * from drm_dp_cec_register_connector() edid == NULL, so in
371 * that case the phys addr is just invalidated.
372 */
373 cec_s_phys_addr_from_edid(aux->cec.adap, edid);
374 }
375unlock:
376 mutex_unlock(&aux->cec.lock);
377}
378EXPORT_SYMBOL(drm_dp_cec_set_edid);
379
380/*
381 * The EDID disappeared (likely because of the HPD going down).
382 */
383void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
384{
385 /* No transfer function was set, so not a DP connector */
386 if (!aux->transfer)
387 return;
388
389 cancel_delayed_work_sync(&aux->cec.unregister_work);
390
391 mutex_lock(&aux->cec.lock);
392 if (!aux->cec.adap)
393 goto unlock;
394
395 cec_phys_addr_invalidate(aux->cec.adap);
396 /*
397 * We're done if we want to keep the CEC device
398 * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
399 * DPCD still indicates the CEC capability (expected for an integrated
400 * HDMI branch device).
401 */
402 if (drm_dp_cec_unregister_delay < NEVER_UNREG_DELAY &&
403 !drm_dp_cec_cap(aux, NULL)) {
404 /*
405 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
406 * seconds. This to debounce short HPD off-and-on cycles from
407 * displays.
408 */
409 schedule_delayed_work(&aux->cec.unregister_work,
410 drm_dp_cec_unregister_delay * HZ);
411 }
412unlock:
413 mutex_unlock(&aux->cec.lock);
414}
415EXPORT_SYMBOL(drm_dp_cec_unset_edid);
416
417/**
418 * drm_dp_cec_register_connector() - register a new connector
419 * @aux: DisplayPort AUX channel
420 * @connector: drm connector
421 *
422 * A new connector was registered with associated CEC adapter name and
423 * CEC adapter parent device. After registering the name and parent
424 * drm_dp_cec_set_edid() is called to check if the connector supports
425 * CEC and to register a CEC adapter if that is the case.
426 */
427void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
428 struct drm_connector *connector)
429{
430 WARN_ON(aux->cec.adap);
431 if (WARN_ON(!aux->transfer))
432 return;
433 aux->cec.connector = connector;
434 INIT_DELAYED_WORK(&aux->cec.unregister_work,
435 drm_dp_cec_unregister_work);
436}
437EXPORT_SYMBOL(drm_dp_cec_register_connector);
438
439/**
440 * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
441 * @aux: DisplayPort AUX channel
442 */
443void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
444{
445 if (!aux->cec.adap)
446 return;
447 cancel_delayed_work_sync(&aux->cec.unregister_work);
448 cec_unregister_adapter(aux->cec.adap);
449 aux->cec.adap = NULL;
450}
451EXPORT_SYMBOL(drm_dp_cec_unregister_connector);