root/drivers/gpu/drm/drm_dp_cec.c

DEFINITIONS

1. drm_dp_cec_adap_enable
2. drm_dp_cec_adap_log_addr
3. drm_dp_cec_adap_transmit
4. drm_dp_cec_adap_monitor_all_enable
5. drm_dp_cec_adap_status
6. drm_dp_cec_received
7. drm_dp_cec_handle_irq
8. drm_dp_cec_irq
9. drm_dp_cec_cap
10. drm_dp_cec_unregister_work
11. drm_dp_cec_set_edid
12. drm_dp_cec_unset_edid
13. drm_dp_cec_register_connector
14. drm_dp_cec_unregister_connector

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