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/export.h>
9#include <linux/kernel.h>
10#include <linux/module.h>
11#include <linux/slab.h>
12
13#include <media/cec.h>
14
15#include <drm/display/drm_dp_helper.h>
16#include <drm/drm_connector.h>
17#include <drm/drm_device.h>
18#include <drm/drm_edid.h>
19
20/*
21 * Unfortunately it turns out that we have a chicken-and-egg situation
22 * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
23 * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
24 * Parade PS176), but they do not wire up the CEC pin, thus making CEC
25 * useless. Note that MegaChips 2900-based adapters appear to have good
26 * support for CEC tunneling. Those adapters that I have tested using
27 * this chipset all have the CEC line connected.
28 *
29 * Sadly there is no way for this driver to know this. What happens is
30 * that a /dev/cecX device is created that is isolated and unable to see
31 * any of the other CEC devices. Quite literally the CEC wire is cut
32 * (or in this case, never connected in the first place).
33 *
34 * The reason so few adapters support this is that this tunneling protocol
35 * was never supported by any OS. So there was no easy way of testing it,
36 * and no incentive to correctly wire up the CEC pin.
37 *
38 * Hopefully by creating this driver it will be easier for vendors to
39 * finally fix their adapters and test the CEC functionality.
40 *
41 * I keep a list of known working adapters here:
42 *
43 * https://hverkuil.home.xs4all.nl/cec-status.txt
44 *
45 * Please mail me (hverkuil@kernel.org) if you find an adapter that works
46 * and is not yet listed there.
47 *
48 * Note that the current implementation does not support CEC over an MST hub.
49 * As far as I can see there is no mechanism defined in the DisplayPort
50 * standard to transport CEC interrupts over an MST device. It might be
51 * possible to do this through polling, but I have not been able to get that
52 * to work.
53 */
54
55/**
56 * DOC: dp cec helpers
57 *
58 * These functions take care of supporting the CEC-Tunneling-over-AUX
59 * feature of DisplayPort-to-HDMI adapters.
60 */
61
62/*
63 * When the EDID is unset because the HPD went low, then the CEC DPCD registers
64 * typically can no longer be read (true for a DP-to-HDMI adapter since it is
65 * powered by the HPD). However, some displays toggle the HPD off and on for a
66 * short period for one reason or another, and that would cause the CEC adapter
67 * to be removed and added again, even though nothing else changed.
68 *
69 * This module parameter sets a delay in seconds before the CEC adapter is
70 * actually unregistered. Only if the HPD does not return within that time will
71 * the CEC adapter be unregistered.
72 *
73 * If it is set to a value >= NEVER_UNREG_DELAY, then the CEC adapter will never
74 * be unregistered for as long as the connector remains registered.
75 *
76 * If it is set to 0, then the CEC adapter will be unregistered immediately as
77 * soon as the HPD disappears.
78 *
79 * The default is one second to prevent short HPD glitches from unregistering
80 * the CEC adapter.
81 *
82 * Note that for integrated HDMI branch devices that support CEC the DPCD
83 * registers remain available even if the HPD goes low since it is not powered
84 * by the HPD. In that case the CEC adapter will never be unregistered during
85 * the life time of the connector. At least, this is the theory since I do not
86 * have hardware with an integrated HDMI branch device that supports CEC.
87 */
88#define NEVER_UNREG_DELAY 1000
89static unsigned int drm_dp_cec_unregister_delay = 1;
90module_param(drm_dp_cec_unregister_delay, uint, 0600);
91MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
92 "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");
93
94static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
95{
96 struct drm_dp_aux *aux = cec_get_drvdata(adap);
97 u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
98 ssize_t err = 0;
99
100 err = drm_dp_dpcd_write_byte(aux, DP_CEC_TUNNELING_CONTROL, value: val);
101 return (enable && err < 0) ? err : 0;
102}
103
104static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
105{
106 struct drm_dp_aux *aux = cec_get_drvdata(adap);
107 /* Bit 15 (logical address 15) should always be set */
108 u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
109 u8 mask[2];
110 ssize_t err;
111
112 if (addr != CEC_LOG_ADDR_INVALID)
113 la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
114 mask[0] = la_mask & 0xff;
115 mask[1] = la_mask >> 8;
116 err = drm_dp_dpcd_write_data(aux, DP_CEC_LOGICAL_ADDRESS_MASK, buffer: mask, size: 2);
117 return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
118}
119
120static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
121 u32 signal_free_time, struct cec_msg *msg)
122{
123 struct drm_dp_aux *aux = cec_get_drvdata(adap);
124 unsigned int retries = min(5, attempts - 1);
125 ssize_t err;
126
127 err = drm_dp_dpcd_write_data(aux, DP_CEC_TX_MESSAGE_BUFFER,
128 buffer: msg->msg, size: msg->len);
129 if (err < 0)
130 return err;
131
132 return drm_dp_dpcd_write_byte(aux, DP_CEC_TX_MESSAGE_INFO,
133 value: (msg->len - 1) | (retries << 4) |
134 DP_CEC_TX_MESSAGE_SEND);
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_read_byte(aux, DP_CEC_TUNNELING_CONTROL, valuep: &val);
148 if (!err) {
149 if (enable)
150 val |= DP_CEC_SNOOPING_ENABLE;
151 else
152 val &= ~DP_CEC_SNOOPING_ENABLE;
153 err = drm_dp_dpcd_write_byte(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_read_byte(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_data(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_read_byte(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_write_byte(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_read_byte(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_write_byte(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_read_byte(aux, DP_CEC_TUNNELING_CAPABILITY, valuep: &cap) < 0 ||
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 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
315
316 mutex_lock(&aux->cec.lock);
317 if (!drm_dp_cec_cap(aux, cec_cap: &cap)) {
318 /* CEC is not supported, unregister any existing adapter */
319 cec_unregister_adapter(adap: aux->cec.adap);
320 aux->cec.adap = NULL;
321 goto unlock;
322 }
323
324 if (cap & DP_CEC_SNOOPING_CAPABLE)
325 cec_caps |= CEC_CAP_MONITOR_ALL;
326 if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
327 num_las = CEC_MAX_LOG_ADDRS;
328
329 if (aux->cec.adap) {
330 /* Check if the adapter properties have changed */
331 if ((aux->cec.adap->capabilities & CEC_CAP_MONITOR_ALL) ==
332 (cec_caps & CEC_CAP_MONITOR_ALL) &&
333 aux->cec.adap->available_log_addrs == num_las) {
334 /* Unchanged, so just set the phys addr */
335 cec_s_phys_addr(adap: aux->cec.adap, phys_addr: source_physical_address, block: false);
336 goto unlock;
337 }
338 /*
339 * The capabilities changed, so unregister the old
340 * adapter first.
341 */
342 cec_unregister_adapter(adap: aux->cec.adap);
343 }
344
345 /* Create a new adapter */
346 aux->cec.adap = cec_allocate_adapter(ops: &drm_dp_cec_adap_ops,
347 priv: aux, name: connector->name, caps: cec_caps,
348 available_las: num_las);
349 if (IS_ERR(ptr: aux->cec.adap)) {
350 aux->cec.adap = NULL;
351 goto unlock;
352 }
353
354 cec_fill_conn_info_from_drm(conn_info: &conn_info, connector);
355 cec_s_conn_info(adap: aux->cec.adap, conn_info: &conn_info);
356
357 if (cec_register_adapter(adap: aux->cec.adap, parent: connector->dev->dev)) {
358 cec_delete_adapter(adap: aux->cec.adap);
359 aux->cec.adap = NULL;
360 } else {
361 /*
362 * Update the phys addr for the new CEC adapter. When called
363 * from drm_dp_cec_register_connector() edid == NULL, so in
364 * that case the phys addr is just invalidated.
365 */
366 cec_s_phys_addr(adap: aux->cec.adap, phys_addr: source_physical_address, block: false);
367 }
368unlock:
369 mutex_unlock(lock: &aux->cec.lock);
370}
371EXPORT_SYMBOL(drm_dp_cec_attach);
372
373/*
374 * Note: Prefer calling drm_dp_cec_attach() with
375 * connector->display_info.source_physical_address if possible.
376 */
377void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
378{
379 u16 pa = CEC_PHYS_ADDR_INVALID;
380
381 if (edid && edid->extensions)
382 pa = cec_get_edid_phys_addr(edid: (const u8 *)edid,
383 EDID_LENGTH * (edid->extensions + 1), NULL);
384
385 drm_dp_cec_attach(aux, pa);
386}
387EXPORT_SYMBOL(drm_dp_cec_set_edid);
388
389/*
390 * The EDID disappeared (likely because of the HPD going down).
391 */
392void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
393{
394 /* No transfer function was set, so not a DP connector */
395 if (!aux->transfer)
396 return;
397
398 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
399
400 mutex_lock(&aux->cec.lock);
401 if (!aux->cec.adap)
402 goto unlock;
403
404 cec_phys_addr_invalidate(adap: aux->cec.adap);
405 /*
406 * We're done if we want to keep the CEC device
407 * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
408 * DPCD still indicates the CEC capability (expected for an integrated
409 * HDMI branch device).
410 */
411 if (drm_dp_cec_unregister_delay < NEVER_UNREG_DELAY &&
412 !drm_dp_cec_cap(aux, NULL)) {
413 /*
414 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
415 * seconds. This to debounce short HPD off-and-on cycles from
416 * displays.
417 */
418 schedule_delayed_work(dwork: &aux->cec.unregister_work,
419 delay: drm_dp_cec_unregister_delay * HZ);
420 }
421unlock:
422 mutex_unlock(lock: &aux->cec.lock);
423}
424EXPORT_SYMBOL(drm_dp_cec_unset_edid);
425
426/**
427 * drm_dp_cec_register_connector() - register a new connector
428 * @aux: DisplayPort AUX channel
429 * @connector: drm connector
430 *
431 * A new connector was registered with associated CEC adapter name and
432 * CEC adapter parent device. After registering the name and parent
433 * drm_dp_cec_set_edid() is called to check if the connector supports
434 * CEC and to register a CEC adapter if that is the case.
435 */
436void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
437 struct drm_connector *connector)
438{
439 WARN_ON(aux->cec.adap);
440 if (WARN_ON(!aux->transfer))
441 return;
442 aux->cec.connector = connector;
443 INIT_DELAYED_WORK(&aux->cec.unregister_work,
444 drm_dp_cec_unregister_work);
445}
446EXPORT_SYMBOL(drm_dp_cec_register_connector);
447
448/**
449 * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
450 * @aux: DisplayPort AUX channel
451 */
452void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
453{
454 if (!aux->cec.adap)
455 return;
456 cancel_delayed_work_sync(dwork: &aux->cec.unregister_work);
457 cec_unregister_adapter(adap: aux->cec.adap);
458 aux->cec.adap = NULL;
459}
460EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
461

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