--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DisplayPort CEC-Tunneling-over-AUX support
+ *
+ * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <drm/drm_dp_helper.h>
+#include <media/cec.h>
+
+/*
+ * Unfortunately it turns out that we have a chicken-and-egg situation
+ * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
+ * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
+ * Parade PS176), but they do not wire up the CEC pin, thus making CEC
+ * useless.
+ *
+ * Sadly there is no way for this driver to know this. What happens is
+ * that a /dev/cecX device is created that is isolated and unable to see
+ * any of the other CEC devices. Quite literally the CEC wire is cut
+ * (or in this case, never connected in the first place).
+ *
+ * The reason so few adapters support this is that this tunneling protocol
+ * was never supported by any OS. So there was no easy way of testing it,
+ * and no incentive to correctly wire up the CEC pin.
+ *
+ * Hopefully by creating this driver it will be easier for vendors to
+ * finally fix their adapters and test the CEC functionality.
+ *
+ * I keep a list of known working adapters here:
+ *
+ * https://hverkuil.home.xs4all.nl/cec-status.txt
+ *
+ * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
+ * and is not yet listed there.
+ *
+ * Note that the current implementation does not support CEC over an MST hub.
+ * As far as I can see there is no mechanism defined in the DisplayPort
+ * standard to transport CEC interrupts over an MST device. It might be
+ * possible to do this through polling, but I have not been able to get that
+ * to work.
+ */
+
+/**
+ * DOC: dp cec helpers
+ *
+ * These functions take care of supporting the CEC-Tunneling-over-AUX
+ * feature of DisplayPort-to-HDMI adapters.
+ */
+
+/*
+ * When the EDID is unset because the HPD went low, then the CEC DPCD registers
+ * typically can no longer be read (true for a DP-to-HDMI adapter since it is
+ * powered by the HPD). However, some displays toggle the HPD off and on for a
+ * short period for one reason or another, and that would cause the CEC adapter
+ * to be removed and added again, even though nothing else changed.
+ *
+ * This module parameter sets a delay in seconds before the CEC adapter is
+ * actually unregistered. Only if the HPD does not return within that time will
+ * the CEC adapter be unregistered.
+ *
+ * If it is set to a value >= NEVER_UNREG_DELAY, then the CEC adapter will never
+ * be unregistered for as long as the connector remains registered.
+ *
+ * If it is set to 0, then the CEC adapter will be unregistered immediately as
+ * soon as the HPD disappears.
+ *
+ * The default is one second to prevent short HPD glitches from unregistering
+ * the CEC adapter.
+ *
+ * Note that for integrated HDMI branch devices that support CEC the DPCD
+ * registers remain available even if the HPD goes low since it is not powered
+ * by the HPD. In that case the CEC adapter will never be unregistered during
+ * the life time of the connector. At least, this is the theory since I do not
+ * have hardware with an integrated HDMI branch device that supports CEC.
+ */
+#define NEVER_UNREG_DELAY 1000
+static unsigned int drm_dp_cec_unregister_delay = 1;
+module_param(drm_dp_cec_unregister_delay, uint, 0600);
+MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
+ "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");
+
+static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
+{
+ struct drm_dp_aux *aux = cec_get_drvdata(adap);
+ u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
+ ssize_t err = 0;
+
+ err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
+ return (enable && err < 0) ? err : 0;
+}
+
+static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
+{
+ struct drm_dp_aux *aux = cec_get_drvdata(adap);
+ /* Bit 15 (logical address 15) should always be set */
+ u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
+ u8 mask[2];
+ ssize_t err;
+
+ if (addr != CEC_LOG_ADDR_INVALID)
+ la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
+ mask[0] = la_mask & 0xff;
+ mask[1] = la_mask >> 8;
+ err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
+ return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
+}
+
+static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
+ u32 signal_free_time, struct cec_msg *msg)
+{
+ struct drm_dp_aux *aux = cec_get_drvdata(adap);
+ unsigned int retries = min(5, attempts - 1);
+ ssize_t err;
+
+ err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
+ msg->msg, msg->len);
+ if (err < 0)
+ return err;
+
+ err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
+ (msg->len - 1) | (retries << 4) |
+ DP_CEC_TX_MESSAGE_SEND);
+ return err < 0 ? err : 0;
+}
+
+static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
+ bool enable)
+{
+ struct drm_dp_aux *aux = cec_get_drvdata(adap);
+ ssize_t err;
+ u8 val;
+
+ if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
+ return 0;
+
+ err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
+ if (err >= 0) {
+ if (enable)
+ val |= DP_CEC_SNOOPING_ENABLE;
+ else
+ val &= ~DP_CEC_SNOOPING_ENABLE;
+ err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
+ }
+ return (enable && err < 0) ? err : 0;
+}
+
+static void drm_dp_cec_adap_status(struct cec_adapter *adap,
+ struct seq_file *file)
+{
+ struct drm_dp_aux *aux = cec_get_drvdata(adap);
+ struct drm_dp_desc desc;
+ struct drm_dp_dpcd_ident *id = &desc.ident;
+
+ if (drm_dp_read_desc(aux, &desc, true))
+ return;
+ seq_printf(file, "OUI: %*pdH\n",
+ (int)sizeof(id->oui), id->oui);
+ seq_printf(file, "ID: %*pE\n",
+ (int)strnlen(id->device_id, sizeof(id->device_id)),
+ id->device_id);
+ seq_printf(file, "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
+ /*
+ * Show this both in decimal and hex: at least one vendor
+ * always reports this in hex.
+ */
+ seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
+ id->sw_major_rev, id->sw_minor_rev,
+ id->sw_major_rev, id->sw_minor_rev);
+}
+
+static const struct cec_adap_ops drm_dp_cec_adap_ops = {
+ .adap_enable = drm_dp_cec_adap_enable,
+ .adap_log_addr = drm_dp_cec_adap_log_addr,
+ .adap_transmit = drm_dp_cec_adap_transmit,
+ .adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
+ .adap_status = drm_dp_cec_adap_status,
+};
+
+static int drm_dp_cec_received(struct drm_dp_aux *aux)
+{
+ struct cec_adapter *adap = aux->cec.adap;
+ struct cec_msg msg;
+ u8 rx_msg_info;
+ ssize_t err;
+
+ err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
+ if (err < 0)
+ return err;
+
+ if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
+ return 0;
+
+ msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
+ err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
+ if (err < 0)
+ return err;
+
+ cec_received_msg(adap, &msg);
+ return 0;
+}
+
+static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
+{
+ struct cec_adapter *adap = aux->cec.adap;
+ u8 flags;
+
+ if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags) < 0)
+ return;
+
+ if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
+ drm_dp_cec_received(aux);
+
+ if (flags & DP_CEC_TX_MESSAGE_SENT)
+ cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
+ else if (flags & DP_CEC_TX_LINE_ERROR)
+ cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
+ CEC_TX_STATUS_MAX_RETRIES);
+ else if (flags &
+ (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
+ cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
+ CEC_TX_STATUS_MAX_RETRIES);
+ drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
+}
+
+/**
+ * drm_dp_cec_irq() - handle CEC interrupt, if any
+ * @aux: DisplayPort AUX channel
+ *
+ * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
+ * is present, then it will check for a CEC_IRQ and handle it accordingly.
+ */
+void drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+ u8 cec_irq;
+ int ret;
+
+ mutex_lock(&aux->cec.lock);
+ if (!aux->cec.adap)
+ goto unlock;
+
+ ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
+ &cec_irq);
+ if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
+ goto unlock;
+
+ drm_dp_cec_handle_irq(aux);
+ drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
+unlock:
+ mutex_unlock(&aux->cec.lock);
+}
+EXPORT_SYMBOL(drm_dp_cec_irq);
+
+static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
+{
+ u8 cap = 0;
+
+ if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
+ !(cap & DP_CEC_TUNNELING_CAPABLE))
+ return false;
+ if (cec_cap)
+ *cec_cap = cap;
+ return true;
+}
+
+/*
+ * Called if the HPD was low for more than drm_dp_cec_unregister_delay
+ * seconds. This unregisters the CEC adapter.
+ */
+static void drm_dp_cec_unregister_work(struct work_struct *work)
+{
+ struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
+ cec.unregister_work.work);
+
+ mutex_lock(&aux->cec.lock);
+ cec_unregister_adapter(aux->cec.adap);
+ aux->cec.adap = NULL;
+ mutex_unlock(&aux->cec.lock);
+}
+
+/*
+ * A new EDID is set. If there is no CEC adapter, then create one. If
+ * there was a CEC adapter, then check if the CEC adapter properties
+ * were unchanged and just update the CEC physical address. Otherwise
+ * unregister the old CEC adapter and create a new one.
+ */
+void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
+{
+ u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
+ unsigned int num_las = 1;
+ u8 cap;
+
+#ifndef CONFIG_MEDIA_CEC_RC
+ /*
+ * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
+ * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
+ *
+ * Do this here as well to ensure the tests against cec_caps are
+ * correct.
+ */
+ cec_caps &= ~CEC_CAP_RC;
+#endif
+ cancel_delayed_work_sync(&aux->cec.unregister_work);
+
+ mutex_lock(&aux->cec.lock);
+ if (!drm_dp_cec_cap(aux, &cap)) {
+ /* CEC is not supported, unregister any existing adapter */
+ cec_unregister_adapter(aux->cec.adap);
+ aux->cec.adap = NULL;
+ goto unlock;
+ }
+
+ if (cap & DP_CEC_SNOOPING_CAPABLE)
+ cec_caps |= CEC_CAP_MONITOR_ALL;
+ if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
+ num_las = CEC_MAX_LOG_ADDRS;
+
+ if (aux->cec.adap) {
+ if (aux->cec.adap->capabilities == cec_caps &&
+ aux->cec.adap->available_log_addrs == num_las) {
+ /* Unchanged, so just set the phys addr */
+ cec_s_phys_addr_from_edid(aux->cec.adap, edid);
+ goto unlock;
+ }
+ /*
+ * The capabilities changed, so unregister the old
+ * adapter first.
+ */
+ cec_unregister_adapter(aux->cec.adap);
+ }
+
+ /* Create a new adapter */
+ aux->cec.adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
+ aux, aux->cec.name, cec_caps,
+ num_las);
+ if (IS_ERR(aux->cec.adap)) {
+ aux->cec.adap = NULL;
+ goto unlock;
+ }
+ if (cec_register_adapter(aux->cec.adap, aux->cec.parent)) {
+ cec_delete_adapter(aux->cec.adap);
+ aux->cec.adap = NULL;
+ } else {
+ /*
+ * Update the phys addr for the new CEC adapter. When called
+ * from drm_dp_cec_register_connector() edid == NULL, so in
+ * that case the phys addr is just invalidated.
+ */
+ cec_s_phys_addr_from_edid(aux->cec.adap, edid);
+ }
+unlock:
+ mutex_unlock(&aux->cec.lock);
+}
+EXPORT_SYMBOL(drm_dp_cec_set_edid);
+
+/*
+ * The EDID disappeared (likely because of the HPD going down).
+ */
+void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
+{
+ cancel_delayed_work_sync(&aux->cec.unregister_work);
+
+ mutex_lock(&aux->cec.lock);
+ if (!aux->cec.adap)
+ goto unlock;
+
+ cec_phys_addr_invalidate(aux->cec.adap);
+ /*
+ * We're done if we want to keep the CEC device
+ * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
+ * DPCD still indicates the CEC capability (expected for an integrated
+ * HDMI branch device).
+ */
+ if (drm_dp_cec_unregister_delay < NEVER_UNREG_DELAY &&
+ !drm_dp_cec_cap(aux, NULL)) {
+ /*
+ * Unregister the CEC adapter after drm_dp_cec_unregister_delay
+ * seconds. This to debounce short HPD off-and-on cycles from
+ * displays.
+ */
+ schedule_delayed_work(&aux->cec.unregister_work,
+ drm_dp_cec_unregister_delay * HZ);
+ }
+unlock:
+ mutex_unlock(&aux->cec.lock);
+}
+EXPORT_SYMBOL(drm_dp_cec_unset_edid);
+
+/**
+ * drm_dp_cec_register_connector() - register a new connector
+ * @aux: DisplayPort AUX channel
+ * @name: name of the CEC device
+ * @parent: parent device
+ *
+ * A new connector was registered with associated CEC adapter name and
+ * CEC adapter parent device. After registering the name and parent
+ * drm_dp_cec_set_edid() is called to check if the connector supports
+ * CEC and to register a CEC adapter if that is the case.
+ */
+void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
+ struct device *parent)
+{
+ WARN_ON(aux->cec.adap);
+ aux->cec.name = name;
+ aux->cec.parent = parent;
+ INIT_DELAYED_WORK(&aux->cec.unregister_work,
+ drm_dp_cec_unregister_work);
+
+ drm_dp_cec_set_edid(aux, NULL);
+}
+EXPORT_SYMBOL(drm_dp_cec_register_connector);
+
+/**
+ * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
+ * @aux: DisplayPort AUX channel
+ */
+void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
+{
+ if (!aux->cec.adap)
+ return;
+ cancel_delayed_work_sync(&aux->cec.unregister_work);
+ cec_unregister_adapter(aux->cec.adap);
+ aux->cec.adap = NULL;
+}
+EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
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