[PATCH 1/3] drm: add support for DisplayPort CEC-Tunneling-over-AUX

[Hans Verkuil <hverkuil@xs4all.nl>]

From: Hans Verkuil <hans.verkuil@cisco.com>

This adds support for the DisplayPort CEC-Tunneling-over-AUX
feature that is part of the DisplayPort 1.3 standard.

Unfortunately, not all DisplayPort/USB-C to HDMI adapters with a
chip that has this capability actually hook up the CEC pin, so
even though a CEC device is created, it may not actually work.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 drivers/gpu/drm/Kconfig      |  10 ++
 drivers/gpu/drm/Makefile     |   1 +
 drivers/gpu/drm/drm_dp_cec.c | 308 +++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_dp_helper.h  |  24 ++++
 4 files changed, 343 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_dp_cec.c

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 83cb2a88c204..1f2708df5c4e 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -120,6 +120,16 @@ config DRM_LOAD_EDID_FIRMWARE
 	  default case is N. Details and instructions how to build your own
 	  EDID data are given in Documentation/EDID/HOWTO.txt.
 
+config DRM_DP_CEC
+	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
+	select CEC_CORE
+	help
+	  Choose this option if you want to enable HDMI CEC support for
+	  DisplayPort/USB-C to HDMI adapters.
+
+	  Note: not all adapters support this feature, and even for those
+	  that do support this they often do not hook up the CEC pin.
+
 config DRM_TTM
 	tristate
 	depends on DRM && MMU
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 24a066e1841c..c6552c62049e 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -40,6 +40,7 @@ drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
 drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
 drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
+drm_kms_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
 
 obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
 obj-$(CONFIG_DRM_DEBUG_MM_SELFTEST) += selftests/
diff --git a/drivers/gpu/drm/drm_dp_cec.c b/drivers/gpu/drm/drm_dp_cec.c
new file mode 100644
index 000000000000..7f2e298d45c0
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_cec.c
@@ -0,0 +1,308 @@
+/*
+ * DisplayPort CEC-Tunneling-over-AUX support
+ *
+ * Copyright 2017 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ *
+ * This program is free software; you may redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#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).
+ *
+ * I suspect that 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.
+ */
+
+/**
+ * DOC: dp cec helpers
+ *
+ * These functions take care of supporting the CEC-Tunneling-over-AUX
+ * feature of DisplayPort-to-HDMI adapters.
+ */
+
+static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	ssize_t err = 0;
+
+	if (enable)
+		err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL,
+					 DP_CEC_TUNNELING_ENABLE);
+	else
+		err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, 0);
+	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);
+	u8 mask[2] = { 0x00, 0x80 };
+	ssize_t err;
+
+	if (addr != CEC_LOG_ADDR_INVALID) {
+		u16 la_mask = adap->log_addrs.log_addr_mask;
+
+		la_mask |= 0x8000 | (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 = 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;
+
+	if (retries > 5)
+		retries = 5;
+	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);
+	u8 buf[DP_AUX_MAX_PAYLOAD_BYTES];
+	u8 hw_rev;
+
+	if (drm_dp_dpcd_read(aux, DP_BRANCH_OUI,
+			     buf, sizeof(buf)) != sizeof(buf))
+		return;
+	hw_rev = buf[9];
+	buf[9] = 0;
+	seq_printf(file, "OUI: %02x-%02x-%02x\n",
+		   buf[0], buf[1], buf[2]);
+	seq_printf(file, "ID: %s\n", buf + 3);
+	seq_printf(file, "HW Rev: %d.%d\n", hw_rev >> 4, 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",
+		   buf[10], buf[11], buf[10], buf[11]);
+}
+
+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 int drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
+{
+	struct cec_adapter *adap = aux->cec_adap;
+	u8 flags;
+	ssize_t err;
+
+	err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags);
+	if (err < 0)
+		return err;
+
+	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);
+	return 0;
+}
+
+/**
+ * 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.
+ *
+ * Returns true if an interrupt was handled successfully or false otherwise.
+ */
+bool drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+	int attempts = 4;
+	bool handled = false;
+
+	if (!aux->cec_adap)
+		return false;
+
+	while (attempts--) {
+		u8 cec_irq;
+		int ret;
+
+		ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
+					&cec_irq);
+		if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
+			break;
+
+		if (!drm_dp_cec_handle_irq(aux))
+			handled = true;
+
+		ret = drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
+					 DP_CEC_IRQ);
+		if (ret < 0)
+			break;
+	}
+	return handled;
+}
+EXPORT_SYMBOL(drm_dp_cec_irq);
+
+/**
+ * drm_dp_cec_configure_adapter() - configure the CEC adapter
+ * @aux: DisplayPort AUX channel
+ * @name: name of the CEC device
+ * @parent: parent device
+ *
+ * Checks if this is a DisplayPort-to-HDMI adapter that supports
+ * CEC-tunneling-over-AUX, and if so it creates a CEC device.
+ *
+ * If a CEC device was already created, then check if the capabilities
+ * have changed. If not, then do nothing. Otherwise destroy the old
+ * CEC device and create a new CEC device.
+ *
+ * This can happen when one DP-to-HDMI adapter is disconnected and
+ * replaced by another adapter with different CEC capabilities.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
+				 struct device *parent)
+{
+	u32 cec_caps = CEC_CAP_LOG_ADDRS | CEC_CAP_TRANSMIT |
+		       CEC_CAP_PASSTHROUGH | CEC_CAP_RC | CEC_CAP_NEEDS_HPD;
+	unsigned int num_las = 1;
+	int err;
+	u8 cap;
+
+	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
+	    !(cap & DP_CEC_TUNNELING_CAPABLE)) {
+		cec_unregister_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+		return -ENODEV;
+	}
+
+	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 (!IS_ERR_OR_NULL(aux->cec_adap)) {
+		if (aux->cec_adap->capabilities == cec_caps &&
+		    aux->cec_adap->available_log_addrs == num_las)
+			return 0;
+		cec_unregister_adapter(aux->cec_adap);
+	}
+
+	aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
+			 aux, name, cec_caps, num_las);
+	if (IS_ERR(aux->cec_adap)) {
+		err = PTR_ERR(aux->cec_adap);
+		aux->cec_adap = NULL;
+		return err;
+	}
+	err = cec_register_adapter(aux->cec_adap, parent);
+	if (err) {
+		cec_delete_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+	}
+	return err;
+}
+EXPORT_SYMBOL(drm_dp_cec_configure_adapter);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index b17476a6909c..0e236dd40b42 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -952,6 +952,8 @@ struct drm_dp_aux_msg {
 	size_t size;
 };
 
+struct cec_adapter;
+
 /**
  * struct drm_dp_aux - DisplayPort AUX channel
  * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
@@ -1010,6 +1012,10 @@ struct drm_dp_aux {
 	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
 	 */
 	unsigned i2c_defer_count;
+	/**
+	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
+	 */
+	struct cec_adapter *cec_adap;
 };
 
 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
@@ -1132,4 +1138,22 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
 	return desc->quirks & BIT(quirk);
 }
 
+#ifdef CONFIG_DRM_DP_CEC
+bool drm_dp_cec_irq(struct drm_dp_aux *aux);
+int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
+				 struct device *parent);
+#else
+static inline bool drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+	return false;
+}
+
+static inline int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux,
+					       const char *name,
+					       struct device *parent)
+{
+	return -ENODEV;
+}
+#endif
+
 #endif /* _DRM_DP_HELPER_H_ */
-- 
2.11.0