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, 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, mask, 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				msg->msg, msg->len);
128	if (err < 0)
129		return err;
130
131	err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
132				 (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, &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, 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, true))
166		return;
167	seq_printf(file, "OUI: %*phD\n",
168		   (int)sizeof(id->oui), id->oui);
169	seq_printf(file, "ID: %*pE\n",
170		   (int)strnlen(id->device_id, sizeof(id->device_id)),
171		   id->device_id);
172	seq_printf(file, "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(file, "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, &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, msg.msg, msg.len);
206	if (err < 0)
207		return err;
208
209	cec_received_msg(adap, &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, &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, 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				&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(&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, &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(aux->cec.adap);
291	aux->cec.adap = NULL;
292	mutex_unlock(&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(&aux->cec.unregister_work);
315
316	mutex_lock(&aux->cec.lock);
317	if (!drm_dp_cec_cap(aux, &cap)) {
318		/* CEC is not supported, unregister any existing adapter */
319		cec_unregister_adapter(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(aux->cec.adap, source_physical_address, false);
336			goto unlock;
337		}
338		/*
339		 * The capabilities changed, so unregister the old
340		 * adapter first.
341		 */
342		cec_unregister_adapter(aux->cec.adap);
343	}
344
345	/* Create a new adapter */
346	aux->cec.adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
347					     aux, connector->name, cec_caps,
348					     num_las);
349	if (IS_ERR(aux->cec.adap)) {
350		aux->cec.adap = NULL;
351		goto unlock;
352	}
353
354	cec_fill_conn_info_from_drm(&conn_info, connector);
355	cec_s_conn_info(aux->cec.adap, &conn_info);
356
357	if (cec_register_adapter(aux->cec.adap, connector->dev->dev)) {
358		cec_delete_adapter(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(aux->cec.adap, source_physical_address, false);
367	}
368unlock:
369	mutex_unlock(&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((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(&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(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(&aux->cec.unregister_work,
419				      drm_dp_cec_unregister_delay * HZ);
420	}
421unlock:
422	mutex_unlock(&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(&aux->cec.unregister_work);
457	cec_unregister_adapter(aux->cec.adap);
458	aux->cec.adap = NULL;
459}
460EXPORT_SYMBOL(drm_dp_cec_unregister_connector);