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/display/drm_dp_helper.h>
15#include <drm/drm_connector.h>
16#include <drm/drm_device.h>
17#include <drm/drm_edid.h>
18
19/*
20 * Unfortunately it turns out that we have a chicken-and-egg situation
21 * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
22 * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
23 * Parade PS176), but they do not wire up the CEC pin, thus making CEC
24 * useless. Note that MegaChips 2900-based adapters appear to have good
25 * support for CEC tunneling. Those adapters that I have tested using
26 * this chipset all have the CEC line connected.
27 *
28 * Sadly there is no way for this driver to know this. What happens is
29 * that a /dev/cecX device is created that is isolated and unable to see
30 * any of the other CEC devices. Quite literally the CEC wire is cut
31 * (or in this case, never connected in the first place).
32 *
33 * The reason so few adapters support this is that this tunneling protocol
34 * was never supported by any OS. So there was no easy way of testing it,
35 * and no incentive to correctly wire up the CEC pin.
36 *
37 * Hopefully by creating this driver it will be easier for vendors to
38 * finally fix their adapters and test the CEC functionality.
39 *
40 * I keep a list of known working adapters here:
41 *
42 * https://hverkuil.home.xs4all.nl/cec-status.txt
43 *
44 * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
45 * and is not yet listed there.
46 *
47 * Note that the current implementation does not support CEC over an MST hub.
48 * As far as I can see there is no mechanism defined in the DisplayPort
49 * standard to transport CEC interrupts over an MST device. It might be
50 * possible to do this through polling, but I have not been able to get that
51 * to work.
52 */
53
54/**
55 * DOC: dp cec helpers
56 *
57 * These functions take care of supporting the CEC-Tunneling-over-AUX
58 * feature of DisplayPort-to-HDMI adapters.
59 */
60
61/*
62 * When the EDID is unset because the HPD went low, then the CEC DPCD registers
63 * typically can no longer be read (true for a DP-to-HDMI adapter since it is
64 * powered by the HPD). However, some displays toggle the HPD off and on for a
65 * short period for one reason or another, and that would cause the CEC adapter
66 * to be removed and added again, even though nothing else changed.
67 *
68 * This module parameter sets a delay in seconds before the CEC adapter is
69 * actually unregistered. Only if the HPD does not return within that time will
70 * the CEC adapter be unregistered.
71 *
72 * If it is set to a value >= NEVER_UNREG_DELAY, then the CEC adapter will never
73 * be unregistered for as long as the connector remains registered.
74 *
75 * If it is set to 0, then the CEC adapter will be unregistered immediately as
76 * soon as the HPD disappears.
77 *
78 * The default is one second to prevent short HPD glitches from unregistering
79 * the CEC adapter.
80 *
81 * Note that for integrated HDMI branch devices that support CEC the DPCD
82 * registers remain available even if the HPD goes low since it is not powered
83 * by the HPD. In that case the CEC adapter will never be unregistered during
84 * the life time of the connector. At least, this is the theory since I do not
85 * have hardware with an integrated HDMI branch device that supports CEC.
86 */
87#define NEVER_UNREG_DELAY 1000
88static unsigned int drm_dp_cec_unregister_delay = 1;
89module_param(drm_dp_cec_unregister_delay, uint, 0600);
90MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
91 "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");
92
93static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
94{
95 struct drm_dp_aux *aux = cec_get_drvdata(adap);
96 u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
97 ssize_t err = 0;
98
99 err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, value: val);
100 return (enable && err < 0) ? err : 0;
101}
102
103static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
104{
105 struct drm_dp_aux *aux = cec_get_drvdata(adap);
106 /* Bit 15 (logical address 15) should always be set */
107 u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
108 u8 mask[2];
109 ssize_t err;
110
111 if (addr != CEC_LOG_ADDR_INVALID)
112 la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
113 mask[0] = la_mask & 0xff;
114 mask[1] = la_mask >> 8;
115 err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, buffer: mask, size: 2);
116 return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
117}
118
119static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
120 u32 signal_free_time, struct cec_msg *msg)
121{
122 struct drm_dp_aux *aux = cec_get_drvdata(adap);
123 unsigned int retries = min(5, attempts - 1);
124 ssize_t err;
125
126 err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
127 buffer: msg->msg, size: msg->len);
128 if (err < 0)
129 return err;
130
131 err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
132 value: (msg->len - 1) | (retries << 4) |
133 DP_CEC_TX_MESSAGE_SEND);
134 return err < 0 ? err : 0;
135}
136
137static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
138 bool enable)
139{
140 struct drm_dp_aux *aux = cec_get_drvdata(adap);
141 ssize_t err;
142 u8 val;
143
144 if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
145 return 0;
146
147 err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, valuep: &val);
148 if (err >= 0) {
149 if (enable)
150 val |= DP_CEC_SNOOPING_ENABLE;
151 else
152 val &= ~DP_CEC_SNOOPING_ENABLE;
153 err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, value: val);
154 }
155 return (enable && err < 0) ? err : 0;
156}
157
158static void drm_dp_cec_adap_status(struct cec_adapter *adap,
159 struct seq_file *file)
160{
161 struct drm_dp_aux *aux = cec_get_drvdata(adap);
162 struct drm_dp_desc desc;
163 struct drm_dp_dpcd_ident *id = &desc.ident;
164
165 if (drm_dp_read_desc(aux, desc: &desc, is_branch: true))
166 return;
167 seq_printf(m: file, fmt: "OUI: %*phD\n",
168 (int)sizeof(id->oui), id->oui);
169 seq_printf(m: file, fmt: "ID: %*pE\n",
170 (int)strnlen(p: id->device_id, maxlen: sizeof(id->device_id)),
171 id->device_id);
172 seq_printf(m: file, fmt: "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
173 /*
174 * Show this both in decimal and hex: at least one vendor
175 * always reports this in hex.
176 */
177 seq_printf(m: file, fmt: "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
178 id->sw_major_rev, id->sw_minor_rev,
179 id->sw_major_rev, id->sw_minor_rev);
180}
181
182static const struct cec_adap_ops drm_dp_cec_adap_ops = {
183 .adap_enable = drm_dp_cec_adap_enable,
184 .adap_log_addr = drm_dp_cec_adap_log_addr,
185 .adap_transmit = drm_dp_cec_adap_transmit,
186 .adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
187 .adap_status = drm_dp_cec_adap_status,
188};
189
190static int drm_dp_cec_received(struct drm_dp_aux *aux)
191{
192 struct cec_adapter *adap = aux->cec.adap;
193 struct cec_msg msg;
194 u8 rx_msg_info;
195 ssize_t err;
196
197 err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, valuep: &rx_msg_info);
198 if (err < 0)
199 return err;
200
201 if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
202 return 0;
203
204 msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
205 err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, buffer: msg.msg, size: msg.len);
206 if (err < 0)
207 return err;
208
209 cec_received_msg(adap, msg: &msg);
210 return 0;
211}
212
213static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
214{
215 struct cec_adapter *adap = aux->cec.adap;
216 u8 flags;
217
218 if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, valuep: &flags) < 0)
219 return;
220
221 if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
222 drm_dp_cec_received(aux);
223
224 if (flags & DP_CEC_TX_MESSAGE_SENT)
225 cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
226 else if (flags & DP_CEC_TX_LINE_ERROR)
227 cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
228 CEC_TX_STATUS_MAX_RETRIES);
229 else if (flags &
230 (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
231 cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
232 CEC_TX_STATUS_MAX_RETRIES);
233 drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, value: flags);
234}
235
236/**
237 * drm_dp_cec_irq() - handle CEC interrupt, if any
238 * @aux: DisplayPort AUX channel
239 *
240 * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
241 * is present, then it will check for a CEC_IRQ and handle it accordingly.
242 */
243void drm_dp_cec_irq(struct drm_dp_aux *aux)
244{
245 u8 cec_irq;
246 int ret;
247
248 /* No transfer function was set, so not a DP connector */
249 if (!aux->transfer)
250 return;
251
252 mutex_lock(&aux->cec.lock);
253 if (!aux->cec.adap)
254 goto unlock;
255
256 ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
257 valuep: &cec_irq);
258 if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
259 goto unlock;
260
261 drm_dp_cec_handle_irq(aux);
262 drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
263unlock:
264 mutex_unlock(lock: &aux->cec.lock);
265}
266EXPORT_SYMBOL(drm_dp_cec_irq);
267
268static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
269{
270 u8 cap = 0;
271
272 if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, valuep: &cap) != 1 ||
273 !(cap & DP_CEC_TUNNELING_CAPABLE))
274 return false;
275 if (cec_cap)
276 *cec_cap = cap;
277 return true;
278}
279
280/*
281 * Called if the HPD was low for more than drm_dp_cec_unregister_delay
282 * seconds. This unregisters the CEC adapter.
283 */
284static void drm_dp_cec_unregister_work(struct work_struct *work)
285{
286 struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
287 cec.unregister_work.work);
288
289 mutex_lock(&aux->cec.lock);
290 cec_unregister_adapter(adap: aux->cec.adap);
291 aux->cec.adap = NULL;
292 mutex_unlock(lock: &aux->cec.lock);
293}
294
295/*
296 * A new EDID is set. If there is no CEC adapter, then create one. If
297 * there was a CEC adapter, then check if the CEC adapter properties
298 * were unchanged and just update the CEC physical address. Otherwise
299 * unregister the old CEC adapter and create a new one.
300 */
301void drm_dp_cec_attach(struct drm_dp_aux *aux, u16 source_physical_address)
302{
303 struct drm_connector *connector = aux->cec.connector;
304 u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD |
305 CEC_CAP_CONNECTOR_INFO;
306 struct cec_connector_info conn_info;
307 unsigned int num_las = 1;
308 u8 cap;
309
310 /* No transfer function was set, so not a DP connector */
311 if (!aux->transfer)
312 return;
313
314#ifndef CONFIG_MEDIA_CEC_RC
315 /*
316 * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
317 * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
318 *
319 * Do this here as well to ensure the tests against cec_caps are
320 * correct.
321 */
322 cec_caps &= ~CEC_CAP_RC;
323#endif
324 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
325
326 mutex_lock(&aux->cec.lock);
327 if (!drm_dp_cec_cap(aux, cec_cap: &cap)) {
328 /* CEC is not supported, unregister any existing adapter */
329 cec_unregister_adapter(adap: aux->cec.adap);
330 aux->cec.adap = NULL;
331 goto unlock;
332 }
333
334 if (cap & DP_CEC_SNOOPING_CAPABLE)
335 cec_caps |= CEC_CAP_MONITOR_ALL;
336 if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
337 num_las = CEC_MAX_LOG_ADDRS;
338
339 if (aux->cec.adap) {
340 if (aux->cec.adap->capabilities == cec_caps &&
341 aux->cec.adap->available_log_addrs == num_las) {
342 /* Unchanged, so just set the phys addr */
343 cec_s_phys_addr(adap: aux->cec.adap, phys_addr: source_physical_address, block: false);
344 goto unlock;
345 }
346 /*
347 * The capabilities changed, so unregister the old
348 * adapter first.
349 */
350 cec_unregister_adapter(adap: aux->cec.adap);
351 }
352
353 /* Create a new adapter */
354 aux->cec.adap = cec_allocate_adapter(ops: &drm_dp_cec_adap_ops,
355 priv: aux, name: connector->name, caps: cec_caps,
356 available_las: num_las);
357 if (IS_ERR(ptr: aux->cec.adap)) {
358 aux->cec.adap = NULL;
359 goto unlock;
360 }
361
362 cec_fill_conn_info_from_drm(conn_info: &conn_info, connector);
363 cec_s_conn_info(adap: aux->cec.adap, conn_info: &conn_info);
364
365 if (cec_register_adapter(adap: aux->cec.adap, parent: connector->dev->dev)) {
366 cec_delete_adapter(adap: aux->cec.adap);
367 aux->cec.adap = NULL;
368 } else {
369 /*
370 * Update the phys addr for the new CEC adapter. When called
371 * from drm_dp_cec_register_connector() edid == NULL, so in
372 * that case the phys addr is just invalidated.
373 */
374 cec_s_phys_addr(adap: aux->cec.adap, phys_addr: source_physical_address, block: false);
375 }
376unlock:
377 mutex_unlock(lock: &aux->cec.lock);
378}
379EXPORT_SYMBOL(drm_dp_cec_attach);
380
381/*
382 * Note: Prefer calling drm_dp_cec_attach() with
383 * connector->display_info.source_physical_address if possible.
384 */
385void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
386{
387 u16 pa = CEC_PHYS_ADDR_INVALID;
388
389 if (edid && edid->extensions)
390 pa = cec_get_edid_phys_addr(edid: (const u8 *)edid,
391 EDID_LENGTH * (edid->extensions + 1), NULL);
392
393 drm_dp_cec_attach(aux, pa);
394}
395EXPORT_SYMBOL(drm_dp_cec_set_edid);
396
397/*
398 * The EDID disappeared (likely because of the HPD going down).
399 */
400void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
401{
402 /* No transfer function was set, so not a DP connector */
403 if (!aux->transfer)
404 return;
405
406 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
407
408 mutex_lock(&aux->cec.lock);
409 if (!aux->cec.adap)
410 goto unlock;
411
412 cec_phys_addr_invalidate(adap: aux->cec.adap);
413 /*
414 * We're done if we want to keep the CEC device
415 * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
416 * DPCD still indicates the CEC capability (expected for an integrated
417 * HDMI branch device).
418 */
419 if (drm_dp_cec_unregister_delay < NEVER_UNREG_DELAY &&
420 !drm_dp_cec_cap(aux, NULL)) {
421 /*
422 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
423 * seconds. This to debounce short HPD off-and-on cycles from
424 * displays.
425 */
426 schedule_delayed_work(dwork: &aux->cec.unregister_work,
427 delay: drm_dp_cec_unregister_delay * HZ);
428 }
429unlock:
430 mutex_unlock(lock: &aux->cec.lock);
431}
432EXPORT_SYMBOL(drm_dp_cec_unset_edid);
433
434/**
435 * drm_dp_cec_register_connector() - register a new connector
436 * @aux: DisplayPort AUX channel
437 * @connector: drm connector
438 *
439 * A new connector was registered with associated CEC adapter name and
440 * CEC adapter parent device. After registering the name and parent
441 * drm_dp_cec_set_edid() is called to check if the connector supports
442 * CEC and to register a CEC adapter if that is the case.
443 */
444void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
445 struct drm_connector *connector)
446{
447 WARN_ON(aux->cec.adap);
448 if (WARN_ON(!aux->transfer))
449 return;
450 aux->cec.connector = connector;
451 INIT_DELAYED_WORK(&aux->cec.unregister_work,
452 drm_dp_cec_unregister_work);
453}
454EXPORT_SYMBOL(drm_dp_cec_register_connector);
455
456/**
457 * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
458 * @aux: DisplayPort AUX channel
459 */
460void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
461{
462 if (!aux->cec.adap)
463 return;
464 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
465 cec_unregister_adapter(adap: aux->cec.adap);
466 aux->cec.adap = NULL;
467}
468EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
469

source code of linux/drivers/gpu/drm/display/drm_dp_cec.c