media: vivid: add signal-free time for cec message xfer

Currently, the vivid emulation of cec message transmission does not force
adapters to wait until the cec bus has been signal-free for a certain
number of bit periods before transmitting or re-transmitting a message.
Without enforcing the signal-free time requirements, adapters do not share
the bus very well and some messages are sent too quickly while other
messages are lost. By emulating a signal-free time and forcing adapters
to wait their turn to transmit, the vivid emulation of cec transmission
is much more reliable.
Signed-off-by: Deborah Brouwer <deborahbrouwer3563@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/test-drivers/vivid/vivid-cec.c

@@ -5,39 +5,22 @@
  * Copyright 2016 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
  */
 
+#include <linux/delay.h>
 #include <media/cec.h>
 
 #include "vivid-core.h"
 #include "vivid-cec.h"
 
-#define CEC_TIM_START_BIT_TOTAL		4500
-#define CEC_TIM_START_BIT_LOW		3700
-#define CEC_TIM_START_BIT_HIGH		800
-#define CEC_TIM_DATA_BIT_TOTAL		2400
-#define CEC_TIM_DATA_BIT_0_LOW		1500
-#define CEC_TIM_DATA_BIT_0_HIGH		900
-#define CEC_TIM_DATA_BIT_1_LOW		600
-#define CEC_TIM_DATA_BIT_1_HIGH		1800
+#define CEC_START_BIT_US		4500
+#define CEC_DATA_BIT_US			2400
+#define CEC_MARGIN_US			350
 
-void vivid_cec_bus_free_work(struct vivid_dev *dev)
-{
-	spin_lock(&dev->cec_slock);
-	while (!list_empty(&dev->cec_work_list)) {
-		struct vivid_cec_work *cw =
-			list_first_entry(&dev->cec_work_list,
-					 struct vivid_cec_work, list);
-
-		spin_unlock(&dev->cec_slock);
-		cancel_delayed_work_sync(&cw->work);
-		spin_lock(&dev->cec_slock);
-		list_del(&cw->list);
-		cec_transmit_attempt_done(cw->adap, CEC_TX_STATUS_LOW_DRIVE);
-		kfree(cw);
-	}
-	spin_unlock(&dev->cec_slock);
-}
+struct xfer_on_bus {
+	struct cec_adapter	*adap;
+	u8			status;
+};
 
-static bool vivid_cec_find_dest_adap(struct vivid_dev *dev,
+static bool find_dest_adap(struct vivid_dev *dev,
 			   struct cec_adapter *adap, u8 dest)
 {
 	unsigned int i;
@@ -61,116 +44,187 @@ static bool vivid_cec_find_dest_adap(struct vivid_dev *dev,
 	return false;
 }
 
-static void vivid_cec_pin_adap_events(struct cec_adapter *adap, ktime_t ts,
-				      const struct cec_msg *msg, bool nacked)
+static bool xfer_ready(struct vivid_dev *dev)
 {
-	unsigned int len = nacked ? 1 : msg->len;
 	unsigned int i;
-	bool bit;
-
-	if (adap == NULL)
-		return;
-
-	/*
-	 * Suffix ULL on constant 10 makes the expression
-	 * CEC_TIM_START_BIT_TOTAL + 10ULL * len * CEC_TIM_DATA_BIT_TOTAL
-	 * to be evaluated using 64-bit unsigned arithmetic (u64), which
-	 * is what ktime_sub_us expects as second argument.
-	 */
-	ts = ktime_sub_us(ts, CEC_TIM_START_BIT_TOTAL +
-			       10ULL * len * CEC_TIM_DATA_BIT_TOTAL);
-	cec_queue_pin_cec_event(adap, false, false, ts);
-	ts = ktime_add_us(ts, CEC_TIM_START_BIT_LOW);
-	cec_queue_pin_cec_event(adap, true, false, ts);
-	ts = ktime_add_us(ts, CEC_TIM_START_BIT_HIGH);
+	bool ready = false;
 
-	for (i = 0; i < 10 * len; i++) {
-		switch (i % 10) {
-		case 0 ... 7:
-			bit = msg->msg[i / 10] & (0x80 >> (i % 10));
-			break;
-		case 8: /* EOM */
-			bit = i / 10 == msg->len - 1;
-			break;
-		case 9: /* ACK */
-			bit = cec_msg_is_broadcast(msg) ^ nacked;
+	spin_lock(&dev->cec_xfers_slock);
+	for (i = 0; i < ARRAY_SIZE(dev->xfers); i++) {
+		if (dev->xfers[i].sft &&
+		    dev->xfers[i].sft <= dev->cec_sft) {
+			ready = true;
 			break;
 		}
-		cec_queue_pin_cec_event(adap, false, false, ts);
-		if (bit)
-			ts = ktime_add_us(ts, CEC_TIM_DATA_BIT_1_LOW);
-		else
-			ts = ktime_add_us(ts, CEC_TIM_DATA_BIT_0_LOW);
-		cec_queue_pin_cec_event(adap, true, false, ts);
-		if (bit)
-			ts = ktime_add_us(ts, CEC_TIM_DATA_BIT_1_HIGH);
-		else
-			ts = ktime_add_us(ts, CEC_TIM_DATA_BIT_0_HIGH);
 	}
+	spin_unlock(&dev->cec_xfers_slock);
+
+	return ready;
 }
 
-static void vivid_cec_pin_events(struct vivid_dev *dev,
-				 const struct cec_msg *msg, bool nacked)
+/*
+ * If an adapter tries to send successive messages, it must wait for the
+ * longest signal-free time between its transmissions. But, if another
+ * adapter sends a message in the interim, then the wait can be reduced
+ * because the messages are no longer successive. Make these adjustments
+ * if necessary. Should be called holding cec_xfers_slock.
+ */
+static void adjust_sfts(struct vivid_dev *dev)
 {
-	ktime_t ts = ktime_get();
 	unsigned int i;
+	u8 initiator;
 
-	vivid_cec_pin_adap_events(dev->cec_rx_adap, ts, msg, nacked);
-	for (i = 0; i < MAX_OUTPUTS; i++)
-		vivid_cec_pin_adap_events(dev->cec_tx_adap[i], ts, msg, nacked);
+	for (i = 0; i < ARRAY_SIZE(dev->xfers); i++) {
+		if (dev->xfers[i].sft <= CEC_SIGNAL_FREE_TIME_RETRY)
+			continue;
+		initiator = dev->xfers[i].msg[0] >> 4;
+		if (initiator == dev->last_initiator)
+			dev->xfers[i].sft = CEC_SIGNAL_FREE_TIME_NEXT_XFER;
+		else
+			dev->xfers[i].sft = CEC_SIGNAL_FREE_TIME_NEW_INITIATOR;
+	}
 }
 
-static void vivid_cec_xfer_done_worker(struct work_struct *work)
+/*
+ * The main emulation of the bus on which CEC adapters attempt to send
+ * messages to each other. The bus keeps track of how long it has been
+ * signal-free and accepts a pending transmission only if the state of
+ * the bus matches the transmission's signal-free requirements. It calls
+ * cec_transmit_attempt_done() for all transmits that enter the bus and
+ * cec_received_msg() for successful transmits.
+ */
+int vivid_cec_bus_thread(void *_dev)
 {
-	struct vivid_cec_work *cw =
-		container_of(work, struct vivid_cec_work, work.work);
-	struct vivid_dev *dev = cw->dev;
-	struct cec_adapter *adap = cw->adap;
-	u8 dest = cec_msg_destination(&cw->msg);
-	bool valid_dest;
+	u32 last_sft;
 	unsigned int i;
+	unsigned int dest;
+	ktime_t start, end;
+	s64 delta_us, retry_us;
+	struct vivid_dev *dev = _dev;
+
+	dev->cec_sft = CEC_SIGNAL_FREE_TIME_NEXT_XFER;
+	for (;;) {
+		bool first = true;
+		int wait_xfer_us = 0;
+		bool valid_dest = false;
+		int wait_arb_lost_us = 0;
+		unsigned int first_idx = 0;
+		unsigned int first_status = 0;
+		struct cec_msg first_msg = {};
+		struct xfer_on_bus xfers_on_bus[MAX_OUTPUTS] = {};
+
+		wait_event_interruptible(dev->kthread_waitq_cec, xfer_ready(dev) ||
+					 kthread_should_stop());
+		if (kthread_should_stop())
+			break;
+		last_sft = dev->cec_sft;
+		dev->cec_sft = 0;
+		/*
+		 * Move the messages that are ready onto the bus. The adapter with
+		 * the most leading zeros will win control of the bus and any other
+		 * adapters will lose arbitration.
+		 */
+		spin_lock(&dev->cec_xfers_slock);
+		for (i = 0; i < ARRAY_SIZE(dev->xfers); i++) {
+			if (!dev->xfers[i].sft || dev->xfers[i].sft > last_sft)
+				continue;
+			if (first) {
+				first = false;
+				first_idx = i;
+				xfers_on_bus[first_idx].adap = dev->xfers[i].adap;
+				memcpy(first_msg.msg, dev->xfers[i].msg, dev->xfers[i].len);
+				first_msg.len = dev->xfers[i].len;
+			} else {
+				xfers_on_bus[i].adap = dev->xfers[i].adap;
+				xfers_on_bus[i].status = CEC_TX_STATUS_ARB_LOST;
+				/*
+				 * For simplicity wait for all 4 bits of the initiator's
+				 * address even though HDMI specification uses bit-level
+				 * precision.
+				 */
+				wait_arb_lost_us = 4 * CEC_DATA_BIT_US + CEC_START_BIT_US;
+			}
+			dev->xfers[i].sft = 0;
+		}
+		dev->last_initiator = cec_msg_initiator(&first_msg);
+		adjust_sfts(dev);
+		spin_unlock(&dev->cec_xfers_slock);
 
-	valid_dest = cec_msg_is_broadcast(&cw->msg);
+		dest = cec_msg_destination(&first_msg);
+		valid_dest = cec_msg_is_broadcast(&first_msg);
 		if (!valid_dest)
-		valid_dest = vivid_cec_find_dest_adap(dev, adap, dest);
-
-	cw->tx_status = valid_dest ? CEC_TX_STATUS_OK : CEC_TX_STATUS_NACK;
-	spin_lock(&dev->cec_slock);
-	dev->cec_xfer_time_jiffies = 0;
-	dev->cec_xfer_start_jiffies = 0;
-	list_del(&cw->list);
-	spin_unlock(&dev->cec_slock);
-	vivid_cec_pin_events(dev, &cw->msg, !valid_dest);
-	cec_transmit_attempt_done(cw->adap, cw->tx_status);
-
-	/* Broadcast message */
-	if (adap != dev->cec_rx_adap)
-		cec_received_msg(dev->cec_rx_adap, &cw->msg);
-	for (i = 0; i < MAX_OUTPUTS && dev->cec_tx_adap[i]; i++)
-		if (adap != dev->cec_tx_adap[i])
-			cec_received_msg(dev->cec_tx_adap[i], &cw->msg);
-	kfree(cw);
-}
-
-static void vivid_cec_xfer_try_worker(struct work_struct *work)
-{
-	struct vivid_cec_work *cw =
-		container_of(work, struct vivid_cec_work, work.work);
-	struct vivid_dev *dev = cw->dev;
-
-	spin_lock(&dev->cec_slock);
-	if (dev->cec_xfer_time_jiffies) {
-		list_del(&cw->list);
-		spin_unlock(&dev->cec_slock);
-		cec_transmit_attempt_done(cw->adap, CEC_TX_STATUS_ARB_LOST);
-		kfree(cw);
+			valid_dest = find_dest_adap(dev, xfers_on_bus[first_idx].adap, dest);
+		if (valid_dest) {
+			first_status = CEC_TX_STATUS_OK;
+			/*
+			 * Message length is in bytes, but each byte is transmitted in
+			 * a block of 10 bits.
+			 */
+			wait_xfer_us = first_msg.len * 10 * CEC_DATA_BIT_US;
 		} else {
-		INIT_DELAYED_WORK(&cw->work, vivid_cec_xfer_done_worker);
-		dev->cec_xfer_start_jiffies = jiffies;
-		dev->cec_xfer_time_jiffies = usecs_to_jiffies(cw->usecs);
-		spin_unlock(&dev->cec_slock);
-		schedule_delayed_work(&cw->work, dev->cec_xfer_time_jiffies);
+			first_status = CEC_TX_STATUS_NACK;
+			/*
+			 * A message that is not acknowledged stops transmitting after
+			 * the header block of 10 bits.
+			 */
+			wait_xfer_us = 10 * CEC_DATA_BIT_US;
+		}
+		wait_xfer_us += CEC_START_BIT_US;
+		xfers_on_bus[first_idx].status = first_status;
+
+		/* Sleep as if sending messages on a real hardware bus. */
+		start = ktime_get();
+		if (wait_arb_lost_us) {
+			usleep_range(wait_arb_lost_us - CEC_MARGIN_US, wait_arb_lost_us);
+			for (i = 0; i < ARRAY_SIZE(xfers_on_bus); i++) {
+				if (xfers_on_bus[i].status != CEC_TX_STATUS_ARB_LOST)
+					continue;
+				cec_transmit_attempt_done(xfers_on_bus[i].adap,
+							  CEC_TX_STATUS_ARB_LOST);
+			}
+			if (kthread_should_stop())
+				break;
+		}
+		wait_xfer_us -= wait_arb_lost_us;
+		usleep_range(wait_xfer_us - CEC_MARGIN_US, wait_xfer_us);
+		cec_transmit_attempt_done(xfers_on_bus[first_idx].adap, first_status);
+		if (kthread_should_stop())
+			break;
+		if (first_status == CEC_TX_STATUS_OK) {
+			if (xfers_on_bus[first_idx].adap != dev->cec_rx_adap)
+				cec_received_msg(dev->cec_rx_adap, &first_msg);
+			for (i = 0; i < MAX_OUTPUTS && dev->cec_tx_adap[i]; i++)
+				if (xfers_on_bus[first_idx].adap != dev->cec_tx_adap[i])
+					cec_received_msg(dev->cec_tx_adap[i], &first_msg);
 		}
+		end = ktime_get();
+		/*
+		 * If the emulated transfer took more or less time than it should
+		 * have, then compensate by adjusting the wait time needed for the
+		 * bus to be signal-free for 3 bit periods (the retry time).
+		 */
+		delta_us = div_s64(end - start, 1000);
+		delta_us -= wait_xfer_us + wait_arb_lost_us;
+		retry_us = CEC_SIGNAL_FREE_TIME_RETRY * CEC_DATA_BIT_US - delta_us;
+		if (retry_us > CEC_MARGIN_US)
+			usleep_range(retry_us - CEC_MARGIN_US, retry_us);
+		dev->cec_sft = CEC_SIGNAL_FREE_TIME_RETRY;
+		/*
+		 * If there are no messages that need to be retried, check if any
+		 * adapters that did not just transmit a message are ready to
+		 * transmit. If none of these adapters are ready, then increase
+		 * the signal-free time so that the bus is available to all
+		 * adapters and go back to waiting for a transmission.
+		 */
+		while (dev->cec_sft >= CEC_SIGNAL_FREE_TIME_RETRY &&
+		       dev->cec_sft < CEC_SIGNAL_FREE_TIME_NEXT_XFER &&
+		       !xfer_ready(dev) && !kthread_should_stop()) {
+			usleep_range(2 * CEC_DATA_BIT_US - CEC_MARGIN_US,
+				     2 * CEC_DATA_BIT_US);
+			dev->cec_sft += 2;
+		}
+	}
+	return 0;
 }
 
 static int vivid_cec_adap_enable(struct cec_adapter *adap, bool enable)
@@ -184,41 +238,26 @@ static int vivid_cec_adap_log_addr(struct cec_adapter *adap, u8 log_addr)
 	return 0;
 }
 
-/*
- * One data bit takes 2400 us, each byte needs 10 bits so that's 24000 us
- * per byte.
- */
-#define USECS_PER_BYTE 24000
-
 static int vivid_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
 				   u32 signal_free_time, struct cec_msg *msg)
 {
 	struct vivid_dev *dev = cec_get_drvdata(adap);
-	struct vivid_cec_work *cw = kzalloc(sizeof(*cw), GFP_KERNEL);
-	long delta_jiffies = 0;
-
-	if (cw == NULL)
-		return -ENOMEM;
-	cw->dev = dev;
-	cw->adap = adap;
-	cw->usecs = CEC_FREE_TIME_TO_USEC(signal_free_time) +
-		    msg->len * USECS_PER_BYTE;
-	cw->msg = *msg;
-
-	spin_lock(&dev->cec_slock);
-	list_add(&cw->list, &dev->cec_work_list);
-	if (dev->cec_xfer_time_jiffies == 0) {
-		INIT_DELAYED_WORK(&cw->work, vivid_cec_xfer_done_worker);
-		dev->cec_xfer_start_jiffies = jiffies;
-		dev->cec_xfer_time_jiffies = usecs_to_jiffies(cw->usecs);
-		delta_jiffies = dev->cec_xfer_time_jiffies;
-	} else {
-		INIT_DELAYED_WORK(&cw->work, vivid_cec_xfer_try_worker);
-		delta_jiffies = dev->cec_xfer_start_jiffies +
-			dev->cec_xfer_time_jiffies - jiffies;
+	u8 idx = cec_msg_initiator(msg);
+
+	spin_lock(&dev->cec_xfers_slock);
+	dev->xfers[idx].adap = adap;
+	memcpy(dev->xfers[idx].msg, msg->msg, CEC_MAX_MSG_SIZE);
+	dev->xfers[idx].len = msg->len;
+	dev->xfers[idx].sft = CEC_SIGNAL_FREE_TIME_RETRY;
+	if (signal_free_time > CEC_SIGNAL_FREE_TIME_RETRY) {
+		if (idx == dev->last_initiator)
+			dev->xfers[idx].sft = CEC_SIGNAL_FREE_TIME_NEXT_XFER;
+		else
+			dev->xfers[idx].sft = CEC_SIGNAL_FREE_TIME_NEW_INITIATOR;
 	}
-	spin_unlock(&dev->cec_slock);
-	schedule_delayed_work(&cw->work, delta_jiffies < 0 ? 0 : delta_jiffies);
+	spin_unlock(&dev->cec_xfers_slock);
+	wake_up_interruptible(&dev->kthread_waitq_cec);
+
 	return 0;
 }
 

drivers/media/test-drivers/vivid/vivid-cec.h

@@ -9,12 +9,5 @@
 struct cec_adapter *vivid_cec_alloc_adap(struct vivid_dev *dev,
 					 unsigned int idx,
 					 bool is_source);
-void vivid_cec_bus_free_work(struct vivid_dev *dev);
-
-#else
-
-static inline void vivid_cec_bus_free_work(struct vivid_dev *dev)
-{
-}
-
+int vivid_cec_bus_thread(void *_dev);
 #endif

drivers/media/test-drivers/vivid/vivid-core.c

@@ -1888,18 +1888,7 @@ static int vivid_create_instance(struct platform_device *pdev, int inst)
 	INIT_LIST_HEAD(&dev->meta_out_active);
 	INIT_LIST_HEAD(&dev->touch_cap_active);
 
-	INIT_LIST_HEAD(&dev->cec_work_list);
-	spin_lock_init(&dev->cec_slock);
-	/*
-	 * Same as create_singlethread_workqueue, but now I can use the
-	 * string formatting of alloc_ordered_workqueue.
-	 */
-	dev->cec_workqueue = alloc_ordered_workqueue("vivid-%03d-cec",
-						     WQ_MEM_RECLAIM, inst);
-	if (!dev->cec_workqueue) {
-		ret = -ENOMEM;
-		goto unreg_dev;
-	}
+	spin_lock_init(&dev->cec_xfers_slock);
 
 	if (allocators[inst] == 1)
 		dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
@@ -1939,6 +1928,19 @@ static int vivid_create_instance(struct platform_device *pdev, int inst)
 			cec_tx_bus_cnt++;
 		}
 	}
+
+	if (dev->cec_rx_adap || cec_tx_bus_cnt) {
+		init_waitqueue_head(&dev->kthread_waitq_cec);
+		dev->kthread_cec = kthread_run(vivid_cec_bus_thread, dev,
+					       "vivid_cec-%s", dev->v4l2_dev.name);
+		if (IS_ERR(dev->kthread_cec)) {
+			dev->kthread_cec = NULL;
+			v4l2_err(&dev->v4l2_dev, "kernel_thread() failed\n");
+			ret = PTR_ERR(dev->kthread_cec);
+			goto unreg_dev;
+		}
+	}
+
 #endif
 
 	v4l2_ctrl_handler_setup(&dev->ctrl_hdl_vid_cap);
@@ -1978,10 +1980,8 @@ static int vivid_create_instance(struct platform_device *pdev, int inst)
 	cec_unregister_adapter(dev->cec_rx_adap);
 	for (i = 0; i < MAX_OUTPUTS; i++)
 		cec_unregister_adapter(dev->cec_tx_adap[i]);
-	if (dev->cec_workqueue) {
-		vivid_cec_bus_free_work(dev);
-		destroy_workqueue(dev->cec_workqueue);
-	}
+	if (dev->kthread_cec)
+		kthread_stop(dev->kthread_cec);
 free_dev:
 	v4l2_device_put(&dev->v4l2_dev);
 	return ret;
@@ -2103,10 +2103,8 @@ static int vivid_remove(struct platform_device *pdev)
 		cec_unregister_adapter(dev->cec_rx_adap);
 		for (j = 0; j < MAX_OUTPUTS; j++)
 			cec_unregister_adapter(dev->cec_tx_adap[j]);
-		if (dev->cec_workqueue) {
-			vivid_cec_bus_free_work(dev);
-			destroy_workqueue(dev->cec_workqueue);
-		}
+		if (dev->kthread_cec)
+			kthread_stop(dev->kthread_cec);
 		v4l2_device_put(&dev->v4l2_dev);
 		vivid_devs[i] = NULL;
 	}

drivers/media/test-drivers/vivid/vivid-core.h

@@ -110,15 +110,11 @@ enum vivid_colorspace {
 #define VIVID_INVALID_SIGNAL(mode) \
 	((mode) == NO_SIGNAL || (mode) == NO_LOCK || (mode) == OUT_OF_RANGE)
 
-struct vivid_cec_work {
-	struct list_head	list;
-	struct delayed_work	work;
+struct vivid_cec_xfer {
 	struct cec_adapter	*adap;
-	struct vivid_dev	*dev;
-	unsigned int		usecs;
-	unsigned int		timeout_ms;
-	u8			tx_status;
-	struct cec_msg		msg;
+	u8			msg[CEC_MAX_MSG_SIZE];
+	u32			len;
+	u32			sft;
 };
 
 struct vivid_dev {
@@ -560,12 +556,13 @@ struct vivid_dev {
 	/* CEC */
 	struct cec_adapter		*cec_rx_adap;
 	struct cec_adapter		*cec_tx_adap[MAX_OUTPUTS];
-	struct workqueue_struct		*cec_workqueue;
-	spinlock_t			cec_slock;
-	struct list_head		cec_work_list;
-	unsigned int			cec_xfer_time_jiffies;
-	unsigned long			cec_xfer_start_jiffies;
 	u8				cec_output2bus_map[MAX_OUTPUTS];
+	struct task_struct		*kthread_cec;
+	wait_queue_head_t		kthread_waitq_cec;
+	struct vivid_cec_xfer	xfers[MAX_OUTPUTS];
+	spinlock_t			cec_xfers_slock; /* read and write cec messages */
+	u32				cec_sft; /* bus signal free time, in bit periods */
+	u8				last_initiator;
 
 	/* CEC OSD String */
 	char				osd[14];