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 
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
87 static unsigned int drm_dp_cec_unregister_delay = 1;
88 module_param(drm_dp_cec_unregister_delay, uint, 0600);
89 MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
90 		 "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");
91 
drm_dp_cec_adap_enable(struct cec_adapter * adap,bool enable)92 static 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 
drm_dp_cec_adap_log_addr(struct cec_adapter * adap,u8 addr)102 static 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 
drm_dp_cec_adap_transmit(struct cec_adapter * adap,u8 attempts,u32 signal_free_time,struct cec_msg * msg)118 static 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 
drm_dp_cec_adap_monitor_all_enable(struct cec_adapter * adap,bool enable)136 static 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 
drm_dp_cec_adap_status(struct cec_adapter * adap,struct seq_file * file)157 static 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 
181 static 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 
drm_dp_cec_received(struct drm_dp_aux * aux)189 static 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 
drm_dp_cec_handle_irq(struct drm_dp_aux * aux)212 static 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  */
drm_dp_cec_irq(struct drm_dp_aux * aux)242 void 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);
262 unlock:
263 	mutex_unlock(&aux->cec.lock);
264 }
265 EXPORT_SYMBOL(drm_dp_cec_irq);
266 
drm_dp_cec_cap(struct drm_dp_aux * aux,u8 * cec_cap)267 static 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  */
drm_dp_cec_unregister_work(struct work_struct * work)283 static 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  */
drm_dp_cec_set_edid(struct drm_dp_aux * aux,const struct edid * edid)300 void 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 	}
375 unlock:
376 	mutex_unlock(&aux->cec.lock);
377 }
378 EXPORT_SYMBOL(drm_dp_cec_set_edid);
379 
380 /*
381  * The EDID disappeared (likely because of the HPD going down).
382  */
drm_dp_cec_unset_edid(struct drm_dp_aux * aux)383 void 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 	}
412 unlock:
413 	mutex_unlock(&aux->cec.lock);
414 }
415 EXPORT_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  */
drm_dp_cec_register_connector(struct drm_dp_aux * aux,struct drm_connector * connector)427 void 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 }
437 EXPORT_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  */
drm_dp_cec_unregister_connector(struct drm_dp_aux * aux)443 void 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 }
451 EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
452