text: // SPDX-License-Identifier: GPL-2.0
  /*
   * core.c - Implementation of core module of MOST Linux driver stack
   *
   * Copyright (C) 2013-2020 Microchip Technology Germany II GmbH & Co. KG
   */
  
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/device.h>
  #include <linux/list.h>
  #include <linux/poll.h>
  #include <linux/wait.h>
  #include <linux/kobject.h>
  #include <linux/mutex.h>
  #include <linux/completion.h>
  #include <linux/sysfs.h>
  #include <linux/kthread.h>
  #include <linux/dma-mapping.h>
  #include <linux/idr.h>
  #include <linux/most.h>
  
  #define MAX_CHANNELS	64
  #define STRING_SIZE	80
  
  static struct ida mdev_id;
  static int dummy_num_buffers;
  static struct list_head comp_list;
  
  struct pipe {
  	struct most_component *comp;
  	int refs;
  	int num_buffers;
  };
  
  struct most_channel {
  	struct device dev;
  	struct completion cleanup;
  	atomic_t mbo_ref;
  	atomic_t mbo_nq_level;
  	u16 channel_id;
  	char name[STRING_SIZE];
  	bool is_poisoned;
  	struct mutex start_mutex; /* channel activation synchronization */
  	struct mutex nq_mutex; /* nq thread synchronization */
  	int is_starving;
  	struct most_interface *iface;
  	struct most_channel_config cfg;
  	bool keep_mbo;
  	bool enqueue_halt;
  	struct list_head fifo;
  	spinlock_t fifo_lock; /* fifo access synchronization */
  	struct list_head halt_fifo;
  	struct list_head list;
  	struct pipe pipe0;
  	struct pipe pipe1;
  	struct list_head trash_fifo;
  	struct task_struct *hdm_enqueue_task;
  	wait_queue_head_t hdm_fifo_wq;
  
  };
  
  #define to_channel(d) container_of(d, struct most_channel, dev)
  
  struct interface_private {
  	int dev_id;
  	char name[STRING_SIZE];
  	struct most_channel *channel[MAX_CHANNELS];
  	struct list_head channel_list;
  };
  
  static const struct {
  	int most_ch_data_type;
  	const char *name;
  } ch_data_type[] = {
  	{ MOST_CH_CONTROL, "control" },
  	{ MOST_CH_ASYNC, "async" },
  	{ MOST_CH_SYNC, "sync" },
  	{ MOST_CH_ISOC, "isoc"},
  	{ MOST_CH_ISOC, "isoc_avp"},
  };
  
  /**
   * list_pop_mbo - retrieves the first MBO of the list and removes it
   * @ptr: the list head to grab the MBO from.
   */
  #define list_pop_mbo(ptr)						\
  ({									\
  	struct mbo *_mbo = list_first_entry(ptr, struct mbo, list);	\
  	list_del(&_mbo->list);						\
  	_mbo;								\
  })
  
  /**
   * most_free_mbo_coherent - free an MBO and its coherent buffer
   * @mbo: most buffer
   */
  static void most_free_mbo_coherent(struct mbo *mbo)
  {
  	struct most_channel *c = mbo->context;
  	u16 const coherent_buf_size = c->cfg.buffer_size + c->cfg.extra_len;
  
  	if (c->iface->dma_free)
  		c->iface->dma_free(mbo, coherent_buf_size);
  	else
  		kfree(mbo->virt_address);
  	kfree(mbo);
  	if (atomic_sub_and_test(1, &c->mbo_ref))
  		complete(&c->cleanup);
  }
  
  /**
   * flush_channel_fifos - clear the channel fifos
   * @c: pointer to channel object
   */
  static void flush_channel_fifos(struct most_channel *c)
  {
  	unsigned long flags, hf_flags;
  	struct mbo *mbo, *tmp;
  
  	if (list_empty(&c->fifo) && list_empty(&c->halt_fifo))
  		return;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	list_for_each_entry_safe(mbo, tmp, &c->fifo, list) {
  		list_del(&mbo->list);
  		spin_unlock_irqrestore(&c->fifo_lock, flags);
  		most_free_mbo_coherent(mbo);
  		spin_lock_irqsave(&c->fifo_lock, flags);
  	}
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  
  	spin_lock_irqsave(&c->fifo_lock, hf_flags);
  	list_for_each_entry_safe(mbo, tmp, &c->halt_fifo, list) {
  		list_del(&mbo->list);
  		spin_unlock_irqrestore(&c->fifo_lock, hf_flags);
  		most_free_mbo_coherent(mbo);
  		spin_lock_irqsave(&c->fifo_lock, hf_flags);
  	}
  	spin_unlock_irqrestore(&c->fifo_lock, hf_flags);
  
  	if (unlikely((!list_empty(&c->fifo) || !list_empty(&c->halt_fifo))))
  		dev_warn(&c->dev, "Channel or trash fifo not empty\n");
  }
  
  /**
   * flush_trash_fifo - clear the trash fifo
   * @c: pointer to channel object
   */
  static int flush_trash_fifo(struct most_channel *c)
  {
  	struct mbo *mbo, *tmp;
  	unsigned long flags;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	list_for_each_entry_safe(mbo, tmp, &c->trash_fifo, list) {
  		list_del(&mbo->list);
  		spin_unlock_irqrestore(&c->fifo_lock, flags);
  		most_free_mbo_coherent(mbo);
  		spin_lock_irqsave(&c->fifo_lock, flags);
  	}
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  	return 0;
  }
  
  static ssize_t available_directions_show(struct device *dev,
  					 struct device_attribute *attr,
  					 char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	strcpy(buf, "");
  	if (c->iface->channel_vector[i].direction & MOST_CH_RX)
  		strcat(buf, "rx ");
  	if (c->iface->channel_vector[i].direction & MOST_CH_TX)
  		strcat(buf, "tx ");
  	strcat(buf, "\n");
  	return strlen(buf);
  }
  
  static ssize_t available_datatypes_show(struct device *dev,
  					struct device_attribute *attr,
  					char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	strcpy(buf, "");
  	if (c->iface->channel_vector[i].data_type & MOST_CH_CONTROL)
  		strcat(buf, "control ");
  	if (c->iface->channel_vector[i].data_type & MOST_CH_ASYNC)
  		strcat(buf, "async ");
  	if (c->iface->channel_vector[i].data_type & MOST_CH_SYNC)
  		strcat(buf, "sync ");
  	if (c->iface->channel_vector[i].data_type & MOST_CH_ISOC)
  		strcat(buf, "isoc ");
  	strcat(buf, "\n");
  	return strlen(buf);
  }
  
  static ssize_t number_of_packet_buffers_show(struct device *dev,
  					     struct device_attribute *attr,
  					     char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	return snprintf(buf, PAGE_SIZE, "%d\n",
  			c->iface->channel_vector[i].num_buffers_packet);
  }
  
  static ssize_t number_of_stream_buffers_show(struct device *dev,
  					     struct device_attribute *attr,
  					     char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	return snprintf(buf, PAGE_SIZE, "%d\n",
  			c->iface->channel_vector[i].num_buffers_streaming);
  }
  
  static ssize_t size_of_packet_buffer_show(struct device *dev,
  					  struct device_attribute *attr,
  					  char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	return snprintf(buf, PAGE_SIZE, "%d\n",
  			c->iface->channel_vector[i].buffer_size_packet);
  }
  
  static ssize_t size_of_stream_buffer_show(struct device *dev,
  					  struct device_attribute *attr,
  					  char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  	unsigned int i = c->channel_id;
  
  	return snprintf(buf, PAGE_SIZE, "%d\n",
  			c->iface->channel_vector[i].buffer_size_streaming);
  }
  
  static ssize_t channel_starving_show(struct device *dev,
  				     struct device_attribute *attr,
  				     char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->is_starving);
  }
  
  static ssize_t set_number_of_buffers_show(struct device *dev,
  					  struct device_attribute *attr,
  					  char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->cfg.num_buffers);
  }
  
  static ssize_t set_buffer_size_show(struct device *dev,
  				    struct device_attribute *attr,
  				    char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->cfg.buffer_size);
  }
  
  static ssize_t set_direction_show(struct device *dev,
  				  struct device_attribute *attr,
  				  char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	if (c->cfg.direction & MOST_CH_TX)
  		return snprintf(buf, PAGE_SIZE, "tx\n");
  	else if (c->cfg.direction & MOST_CH_RX)
  		return snprintf(buf, PAGE_SIZE, "rx\n");
  	return snprintf(buf, PAGE_SIZE, "unconfigured\n");
  }
  
  static ssize_t set_datatype_show(struct device *dev,
  				 struct device_attribute *attr,
  				 char *buf)
  {
  	int i;
  	struct most_channel *c = to_channel(dev);
  
  	for (i = 0; i < ARRAY_SIZE(ch_data_type); i++) {
  		if (c->cfg.data_type & ch_data_type[i].most_ch_data_type)
  			return snprintf(buf, PAGE_SIZE, "%s",
  					ch_data_type[i].name);
  	}
  	return snprintf(buf, PAGE_SIZE, "unconfigured\n");
  }
  
  static ssize_t set_subbuffer_size_show(struct device *dev,
  				       struct device_attribute *attr,
  				       char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->cfg.subbuffer_size);
  }
  
  static ssize_t set_packets_per_xact_show(struct device *dev,
  					 struct device_attribute *attr,
  					 char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->cfg.packets_per_xact);
  }
  
  static ssize_t set_dbr_size_show(struct device *dev,
  				 struct device_attribute *attr, char *buf)
  {
  	struct most_channel *c = to_channel(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%d\n", c->cfg.dbr_size);
  }
  
  #define to_dev_attr(a) container_of(a, struct device_attribute, attr)
  static umode_t channel_attr_is_visible(struct kobject *kobj,
  				       struct attribute *attr, int index)
  {
  	struct device_attribute *dev_attr = to_dev_attr(attr);
  	struct device *dev = kobj_to_dev(kobj);
  	struct most_channel *c = to_channel(dev);
  
  	if (!strcmp(dev_attr->attr.name, "set_dbr_size") &&
  	    (c->iface->interface != ITYPE_MEDIALB_DIM2))
  		return 0;
  	if (!strcmp(dev_attr->attr.name, "set_packets_per_xact") &&
  	    (c->iface->interface != ITYPE_USB))
  		return 0;
  
  	return attr->mode;
  }
  
  #define DEV_ATTR(_name)  (&dev_attr_##_name.attr)
  
  static DEVICE_ATTR_RO(available_directions);
  static DEVICE_ATTR_RO(available_datatypes);
  static DEVICE_ATTR_RO(number_of_packet_buffers);
  static DEVICE_ATTR_RO(number_of_stream_buffers);
  static DEVICE_ATTR_RO(size_of_stream_buffer);
  static DEVICE_ATTR_RO(size_of_packet_buffer);
  static DEVICE_ATTR_RO(channel_starving);
  static DEVICE_ATTR_RO(set_buffer_size);
  static DEVICE_ATTR_RO(set_number_of_buffers);
  static DEVICE_ATTR_RO(set_direction);
  static DEVICE_ATTR_RO(set_datatype);
  static DEVICE_ATTR_RO(set_subbuffer_size);
  static DEVICE_ATTR_RO(set_packets_per_xact);
  static DEVICE_ATTR_RO(set_dbr_size);
  
  static struct attribute *channel_attrs[] = {
  	DEV_ATTR(available_directions),
  	DEV_ATTR(available_datatypes),
  	DEV_ATTR(number_of_packet_buffers),
  	DEV_ATTR(number_of_stream_buffers),
  	DEV_ATTR(size_of_stream_buffer),
  	DEV_ATTR(size_of_packet_buffer),
  	DEV_ATTR(channel_starving),
  	DEV_ATTR(set_buffer_size),
  	DEV_ATTR(set_number_of_buffers),
  	DEV_ATTR(set_direction),
  	DEV_ATTR(set_datatype),
  	DEV_ATTR(set_subbuffer_size),
  	DEV_ATTR(set_packets_per_xact),
  	DEV_ATTR(set_dbr_size),
  	NULL,
  };
  
  static struct attribute_group channel_attr_group = {
  	.attrs = channel_attrs,
  	.is_visible = channel_attr_is_visible,
  };
  
  static const struct attribute_group *channel_attr_groups[] = {
  	&channel_attr_group,
  	NULL,
  };
  
  static ssize_t description_show(struct device *dev,
  				struct device_attribute *attr,
  				char *buf)
  {
  	struct most_interface *iface = dev_get_drvdata(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%s\n", iface->description);
  }
  
  static ssize_t interface_show(struct device *dev,
  			      struct device_attribute *attr,
  			      char *buf)
  {
  	struct most_interface *iface = dev_get_drvdata(dev);
  
  	switch (iface->interface) {
  	case ITYPE_LOOPBACK:
  		return snprintf(buf, PAGE_SIZE, "loopback\n");
  	case ITYPE_I2C:
  		return snprintf(buf, PAGE_SIZE, "i2c\n");
  	case ITYPE_I2S:
  		return snprintf(buf, PAGE_SIZE, "i2s\n");
  	case ITYPE_TSI:
  		return snprintf(buf, PAGE_SIZE, "tsi\n");
  	case ITYPE_HBI:
  		return snprintf(buf, PAGE_SIZE, "hbi\n");
  	case ITYPE_MEDIALB_DIM:
  		return snprintf(buf, PAGE_SIZE, "mlb_dim\n");
  	case ITYPE_MEDIALB_DIM2:
  		return snprintf(buf, PAGE_SIZE, "mlb_dim2\n");
  	case ITYPE_USB:
  		return snprintf(buf, PAGE_SIZE, "usb\n");
  	case ITYPE_PCIE:
  		return snprintf(buf, PAGE_SIZE, "pcie\n");
  	}
  	return snprintf(buf, PAGE_SIZE, "unknown\n");
  }
  
  static DEVICE_ATTR_RO(description);
  static DEVICE_ATTR_RO(interface);
  
  static struct attribute *interface_attrs[] = {
  	DEV_ATTR(description),
  	DEV_ATTR(interface),
  	NULL,
  };
  
  static struct attribute_group interface_attr_group = {
  	.attrs = interface_attrs,
  };
  
  static const struct attribute_group *interface_attr_groups[] = {
  	&interface_attr_group,
  	NULL,
  };
  
  static struct most_component *match_component(char *name)
  {
  	struct most_component *comp;
  
  	list_for_each_entry(comp, &comp_list, list) {
  		if (!strcmp(comp->name, name))
  			return comp;
  	}
  	return NULL;
  }
  
  struct show_links_data {
  	int offs;
  	char *buf;
  };
  
  static int print_links(struct device *dev, void *data)
  {
  	struct show_links_data *d = data;
  	int offs = d->offs;
  	char *buf = d->buf;
  	struct most_channel *c;
  	struct most_interface *iface = dev_get_drvdata(dev);
  
  	list_for_each_entry(c, &iface->p->channel_list, list) {
  		if (c->pipe0.comp) {
  			offs += scnprintf(buf + offs,
  					 PAGE_SIZE - offs,
  					 "%s:%s:%s\n",
  					 c->pipe0.comp->name,
  					 dev_name(iface->dev),
  					 dev_name(&c->dev));
  		}
  		if (c->pipe1.comp) {
  			offs += scnprintf(buf + offs,
  					 PAGE_SIZE - offs,
  					 "%s:%s:%s\n",
  					 c->pipe1.comp->name,
  					 dev_name(iface->dev),
  					 dev_name(&c->dev));
  		}
  	}
  	d->offs = offs;
  	return 0;
  }
  
  static int most_match(struct device *dev, struct device_driver *drv)
  {
  	if (!strcmp(dev_name(dev), "most"))
  		return 0;
  	else
  		return 1;
  }
  
  static struct bus_type mostbus = {
  	.name = "most",
  	.match = most_match,
  };
  
  static ssize_t links_show(struct device_driver *drv, char *buf)
  {
  	struct show_links_data d = { .buf = buf };
  
  	bus_for_each_dev(&mostbus, NULL, &d, print_links);
  	return d.offs;
  }
  
  static ssize_t components_show(struct device_driver *drv, char *buf)
  {
  	struct most_component *comp;
  	int offs = 0;
  
  	list_for_each_entry(comp, &comp_list, list) {
  		offs += scnprintf(buf + offs, PAGE_SIZE - offs, "%s\n",
  				 comp->name);
  	}
  	return offs;
  }
  
  /**
   * get_channel - get pointer to channel
   * @mdev: name of the device interface
   * @mdev_ch: name of channel
   */
  static struct most_channel *get_channel(char *mdev, char *mdev_ch)
  {
  	struct device *dev = NULL;
  	struct most_interface *iface;
  	struct most_channel *c, *tmp;
  
  	dev = bus_find_device_by_name(&mostbus, NULL, mdev);
  	if (!dev)
  		return NULL;
  	put_device(dev);
  	iface = dev_get_drvdata(dev);
  	list_for_each_entry_safe(c, tmp, &iface->p->channel_list, list) {
  		if (!strcmp(dev_name(&c->dev), mdev_ch))
  			return c;
  	}
  	return NULL;
  }
  
  static
  inline int link_channel_to_component(struct most_channel *c,
  				     struct most_component *comp,
  				     char *name,
  				     char *comp_param)
  {
  	int ret;
  	struct most_component **comp_ptr;
  
  	if (!c->pipe0.comp)
  		comp_ptr = &c->pipe0.comp;
  	else if (!c->pipe1.comp)
  		comp_ptr = &c->pipe1.comp;
  	else
  		return -ENOSPC;
  
  	*comp_ptr = comp;
  	ret = comp->probe_channel(c->iface, c->channel_id, &c->cfg, name,
  				  comp_param);
  	if (ret) {
  		*comp_ptr = NULL;
  		return ret;
  	}
  	return 0;
  }
  
  int most_set_cfg_buffer_size(char *mdev, char *mdev_ch, u16 val)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	c->cfg.buffer_size = val;
  	return 0;
  }
  
  int most_set_cfg_subbuffer_size(char *mdev, char *mdev_ch, u16 val)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	c->cfg.subbuffer_size = val;
  	return 0;
  }
  
  int most_set_cfg_dbr_size(char *mdev, char *mdev_ch, u16 val)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	c->cfg.dbr_size = val;
  	return 0;
  }
  
  int most_set_cfg_num_buffers(char *mdev, char *mdev_ch, u16 val)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	c->cfg.num_buffers = val;
  	return 0;
  }
  
  int most_set_cfg_datatype(char *mdev, char *mdev_ch, char *buf)
  {
  	int i;
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	for (i = 0; i < ARRAY_SIZE(ch_data_type); i++) {
  		if (!strcmp(buf, ch_data_type[i].name)) {
  			c->cfg.data_type = ch_data_type[i].most_ch_data_type;
  			break;
  		}
  	}
  
  	if (i == ARRAY_SIZE(ch_data_type))
  		dev_warn(&c->dev, "Invalid attribute settings\n");
  	return 0;
  }
  
  int most_set_cfg_direction(char *mdev, char *mdev_ch, char *buf)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	if (!strcmp(buf, "dir_rx")) {
  		c->cfg.direction = MOST_CH_RX;
  	} else if (!strcmp(buf, "rx")) {
  		c->cfg.direction = MOST_CH_RX;
  	} else if (!strcmp(buf, "dir_tx")) {
  		c->cfg.direction = MOST_CH_TX;
  	} else if (!strcmp(buf, "tx")) {
  		c->cfg.direction = MOST_CH_TX;
  	} else {
  		dev_err(&c->dev, "Invalid direction\n");
  		return -ENODATA;
  	}
  	return 0;
  }
  
  int most_set_cfg_packets_xact(char *mdev, char *mdev_ch, u16 val)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  
  	if (!c)
  		return -ENODEV;
  	c->cfg.packets_per_xact = val;
  	return 0;
  }
  
  int most_cfg_complete(char *comp_name)
  {
  	struct most_component *comp;
  
  	comp = match_component(comp_name);
  	if (!comp)
  		return -ENODEV;
  
  	return comp->cfg_complete();
  }
  
  int most_add_link(char *mdev, char *mdev_ch, char *comp_name, char *link_name,
  		  char *comp_param)
  {
  	struct most_channel *c = get_channel(mdev, mdev_ch);
  	struct most_component *comp = match_component(comp_name);
  
  	if (!c || !comp)
  		return -ENODEV;
  
  	return link_channel_to_component(c, comp, link_name, comp_param);
  }
  
  int most_remove_link(char *mdev, char *mdev_ch, char *comp_name)
  {
  	struct most_channel *c;
  	struct most_component *comp;
  
  	comp = match_component(comp_name);
  	if (!comp)
  		return -ENODEV;
  	c = get_channel(mdev, mdev_ch);
  	if (!c)
  		return -ENODEV;
  
  	if (comp->disconnect_channel(c->iface, c->channel_id))
  		return -EIO;
  	if (c->pipe0.comp == comp)
  		c->pipe0.comp = NULL;
  	if (c->pipe1.comp == comp)
  		c->pipe1.comp = NULL;
  	return 0;
  }
  
  #define DRV_ATTR(_name)  (&driver_attr_##_name.attr)
  
  static DRIVER_ATTR_RO(links);
  static DRIVER_ATTR_RO(components);
  
  static struct attribute *mc_attrs[] = {
  	DRV_ATTR(links),
  	DRV_ATTR(components),
  	NULL,
  };
  
  static struct attribute_group mc_attr_group = {
  	.attrs = mc_attrs,
  };
  
  static const struct attribute_group *mc_attr_groups[] = {
  	&mc_attr_group,
  	NULL,
  };
  
  static struct device_driver mostbus_driver = {
  	.name = "most_core",
  	.bus = &mostbus,
  	.groups = mc_attr_groups,
  };
  
  static inline void trash_mbo(struct mbo *mbo)
  {
  	unsigned long flags;
  	struct most_channel *c = mbo->context;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	list_add(&mbo->list, &c->trash_fifo);
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  }
  
  static bool hdm_mbo_ready(struct most_channel *c)
  {
  	bool empty;
  
  	if (c->enqueue_halt)
  		return false;
  
  	spin_lock_irq(&c->fifo_lock);
  	empty = list_empty(&c->halt_fifo);
  	spin_unlock_irq(&c->fifo_lock);
  
  	return !empty;
  }
  
  static void nq_hdm_mbo(struct mbo *mbo)
  {
  	unsigned long flags;
  	struct most_channel *c = mbo->context;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	list_add_tail(&mbo->list, &c->halt_fifo);
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  	wake_up_interruptible(&c->hdm_fifo_wq);
  }
  
  static int hdm_enqueue_thread(void *data)
  {
  	struct most_channel *c = data;
  	struct mbo *mbo;
  	int ret;
  	typeof(c->iface->enqueue) enqueue = c->iface->enqueue;
  
  	while (likely(!kthread_should_stop())) {
  		wait_event_interruptible(c->hdm_fifo_wq,
  					 hdm_mbo_ready(c) ||
  					 kthread_should_stop());
  
  		mutex_lock(&c->nq_mutex);
  		spin_lock_irq(&c->fifo_lock);
  		if (unlikely(c->enqueue_halt || list_empty(&c->halt_fifo))) {
  			spin_unlock_irq(&c->fifo_lock);
  			mutex_unlock(&c->nq_mutex);
  			continue;
  		}
  
  		mbo = list_pop_mbo(&c->halt_fifo);
  		spin_unlock_irq(&c->fifo_lock);
  
  		if (c->cfg.direction == MOST_CH_RX)
  			mbo->buffer_length = c->cfg.buffer_size;
  
  		ret = enqueue(mbo->ifp, mbo->hdm_channel_id, mbo);
  		mutex_unlock(&c->nq_mutex);
  
  		if (unlikely(ret)) {
  			dev_err(&c->dev, "Buffer enqueue failed\n");
  			nq_hdm_mbo(mbo);
  			c->hdm_enqueue_task = NULL;
  			return 0;
  		}
  	}
  
  	return 0;
  }
  
  static int run_enqueue_thread(struct most_channel *c, int channel_id)
  {
  	struct task_struct *task =
  		kthread_run(hdm_enqueue_thread, c, "hdm_fifo_%d",
  			    channel_id);
  
  	if (IS_ERR(task))
  		return PTR_ERR(task);
  
  	c->hdm_enqueue_task = task;
  	return 0;
  }
  
  /**
   * arm_mbo - recycle MBO for further usage
   * @mbo: most buffer
   *
   * This puts an MBO back to the list to have it ready for up coming
   * tx transactions.
   *
   * In case the MBO belongs to a channel that recently has been
   * poisoned, the MBO is scheduled to be trashed.
   * Calls the completion handler of an attached component.
   */
  static void arm_mbo(struct mbo *mbo)
  {
  	unsigned long flags;
  	struct most_channel *c;
  
  	c = mbo->context;
  
  	if (c->is_poisoned) {
  		trash_mbo(mbo);
  		return;
  	}
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	++*mbo->num_buffers_ptr;
  	list_add_tail(&mbo->list, &c->fifo);
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  
  	if (c->pipe0.refs && c->pipe0.comp->tx_completion)
  		c->pipe0.comp->tx_completion(c->iface, c->channel_id);
  
  	if (c->pipe1.refs && c->pipe1.comp->tx_completion)
  		c->pipe1.comp->tx_completion(c->iface, c->channel_id);
  }
  
  /**
   * arm_mbo_chain - helper function that arms an MBO chain for the HDM
   * @c: pointer to interface channel
   * @dir: direction of the channel
   * @compl: pointer to completion function
   *
   * This allocates buffer objects including the containing DMA coherent
   * buffer and puts them in the fifo.
   * Buffers of Rx channels are put in the kthread fifo, hence immediately
   * submitted to the HDM.
   *
   * Returns the number of allocated and enqueued MBOs.
   */
  static int arm_mbo_chain(struct most_channel *c, int dir,
  			 void (*compl)(struct mbo *))
  {
  	unsigned int i;
  	struct mbo *mbo;
  	unsigned long flags;
  	u32 coherent_buf_size = c->cfg.buffer_size + c->cfg.extra_len;
  
  	atomic_set(&c->mbo_nq_level, 0);
  
  	for (i = 0; i < c->cfg.num_buffers; i++) {
  		mbo = kzalloc(sizeof(*mbo), GFP_KERNEL);
  		if (!mbo)
  			goto flush_fifos;
  
  		mbo->context = c;
  		mbo->ifp = c->iface;
  		mbo->hdm_channel_id = c->channel_id;
  		if (c->iface->dma_alloc) {
  			mbo->virt_address =
  				c->iface->dma_alloc(mbo, coherent_buf_size);
  		} else {
  			mbo->virt_address =
  				kzalloc(coherent_buf_size, GFP_KERNEL);
  		}
  		if (!mbo->virt_address)
  			goto release_mbo;
  
  		mbo->complete = compl;
  		mbo->num_buffers_ptr = &dummy_num_buffers;
  		if (dir == MOST_CH_RX) {
  			nq_hdm_mbo(mbo);
  			atomic_inc(&c->mbo_nq_level);
  		} else {
  			spin_lock_irqsave(&c->fifo_lock, flags);
  			list_add_tail(&mbo->list, &c->fifo);
  			spin_unlock_irqrestore(&c->fifo_lock, flags);
  		}
  	}
  	return c->cfg.num_buffers;
  
  release_mbo:
  	kfree(mbo);
  
  flush_fifos:
  	flush_channel_fifos(c);
  	return 0;
  }
  
  /**
   * most_submit_mbo - submits an MBO to fifo
   * @mbo: most buffer
   */
  void most_submit_mbo(struct mbo *mbo)
  {
  	if (WARN_ONCE(!mbo || !mbo->context,
  		      "Bad buffer or missing channel reference\n"))
  		return;
  
  	nq_hdm_mbo(mbo);
  }
  EXPORT_SYMBOL_GPL(most_submit_mbo);
  
  /**
   * most_write_completion - write completion handler
   * @mbo: most buffer
   *
   * This recycles the MBO for further usage. In case the channel has been
   * poisoned, the MBO is scheduled to be trashed.
   */
  static void most_write_completion(struct mbo *mbo)
  {
  	struct most_channel *c;
  
  	c = mbo->context;
  	if (unlikely(c->is_poisoned || (mbo->status == MBO_E_CLOSE)))
  		trash_mbo(mbo);
  	else
  		arm_mbo(mbo);
  }
  
  int channel_has_mbo(struct most_interface *iface, int id,
  		    struct most_component *comp)
  {
  	struct most_channel *c = iface->p->channel[id];
  	unsigned long flags;
  	int empty;
  
  	if (unlikely(!c))
  		return -EINVAL;
  
  	if (c->pipe0.refs && c->pipe1.refs &&
  	    ((comp == c->pipe0.comp && c->pipe0.num_buffers <= 0) ||
  	     (comp == c->pipe1.comp && c->pipe1.num_buffers <= 0)))
  		return 0;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	empty = list_empty(&c->fifo);
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  	return !empty;
  }
  EXPORT_SYMBOL_GPL(channel_has_mbo);
  
  /**
   * most_get_mbo - get pointer to an MBO of pool
   * @iface: pointer to interface instance
   * @id: channel ID
   * @comp: driver component
   *
   * This attempts to get a free buffer out of the channel fifo.
   * Returns a pointer to MBO on success or NULL otherwise.
   */
  struct mbo *most_get_mbo(struct most_interface *iface, int id,
  			 struct most_component *comp)
  {
  	struct mbo *mbo;
  	struct most_channel *c;
  	unsigned long flags;
  	int *num_buffers_ptr;
  
  	c = iface->p->channel[id];
  	if (unlikely(!c))
  		return NULL;
  
  	if (c->pipe0.refs && c->pipe1.refs &&
  	    ((comp == c->pipe0.comp && c->pipe0.num_buffers <= 0) ||
  	     (comp == c->pipe1.comp && c->pipe1.num_buffers <= 0)))
  		return NULL;
  
  	if (comp == c->pipe0.comp)
  		num_buffers_ptr = &c->pipe0.num_buffers;
  	else if (comp == c->pipe1.comp)
  		num_buffers_ptr = &c->pipe1.num_buffers;
  	else
  		num_buffers_ptr = &dummy_num_buffers;
  
  	spin_lock_irqsave(&c->fifo_lock, flags);
  	if (list_empty(&c->fifo)) {
  		spin_unlock_irqrestore(&c->fifo_lock, flags);
  		return NULL;
  	}
  	mbo = list_pop_mbo(&c->fifo);
  	--*num_buffers_ptr;
  	spin_unlock_irqrestore(&c->fifo_lock, flags);
  
  	mbo->num_buffers_ptr = num_buffers_ptr;
  	mbo->buffer_length = c->cfg.buffer_size;
  	return mbo;
  }
  EXPORT_SYMBOL_GPL(most_get_mbo);
  
  /**
   * most_put_mbo - return buffer to pool
   * @mbo: most buffer
   */
  void most_put_mbo(struct mbo *mbo)
  {
  	struct most_channel *c = mbo->context;
  
  	if (c->cfg.direction == MOST_CH_TX) {
  		arm_mbo(mbo);
  		return;
  	}
  	nq_hdm_mbo(mbo);
  	atomic_inc(&c->mbo_nq_level);
  }
  EXPORT_SYMBOL_GPL(most_put_mbo);
  
  /**
   * most_read_completion - read completion handler
   * @mbo: most buffer
   *
   * This function is called by the HDM when data has been received from the
   * hardware and copied to the buffer of the MBO.
   *
   * In case the channel has been poisoned it puts the buffer in the trash queue.
   * Otherwise, it passes the buffer to an component for further processing.
   */
  static void most_read_completion(struct mbo *mbo)
  {
  	struct most_channel *c = mbo->context;
  
  	if (unlikely(c->is_poisoned || (mbo->status == MBO_E_CLOSE))) {
  		trash_mbo(mbo);
  		return;
  	}
  
  	if (mbo->status == MBO_E_INVAL) {
  		nq_hdm_mbo(mbo);
  		atomic_inc(&c->mbo_nq_level);
  		return;
  	}
  
  	if (atomic_sub_and_test(1, &c->mbo_nq_level))
  		c->is_starving = 1;
  
  	if (c->pipe0.refs && c->pipe0.comp->rx_completion &&
  	    c->pipe0.comp->rx_completion(mbo) == 0)
  		return;
  
  	if (c->pipe1.refs && c->pipe1.comp->rx_completion &&
  	    c->pipe1.comp->rx_completion(mbo) == 0)
  		return;
  
  	most_put_mbo(mbo);
  }
  
  /**
   * most_start_channel - prepares a channel for communication
   * @iface: pointer to interface instance
   * @id: channel ID
   * @comp: driver component
   *
   * This prepares the channel for usage. Cross-checks whether the
   * channel's been properly configured.
   *
   * Returns 0 on success or error code otherwise.
   */
  int most_start_channel(struct most_interface *iface, int id,
  		       struct most_component *comp)
  {
  	int num_buffer;
  	int ret;
  	struct most_channel *c = iface->p->channel[id];
  
  	if (unlikely(!c))
  		return -EINVAL;
  
  	mutex_lock(&c->start_mutex);
  	if (c->pipe0.refs + c->pipe1.refs > 0)
  		goto out; /* already started by another component */
  
  	if (!try_module_get(iface->mod)) {
  		dev_err(&c->dev, "Failed to acquire HDM lock\n");
  		mutex_unlock(&c->start_mutex);
  		return -ENOLCK;
  	}
  
  	c->cfg.extra_len = 0;
  	if (c->iface->configure(c->iface, c->channel_id, &c->cfg)) {
  		dev_err(&c->dev, "Channel configuration failed. Go check settings...\n");
  		ret = -EINVAL;
  		goto err_put_module;
  	}
  
  	init_waitqueue_head(&c->hdm_fifo_wq);
  
  	if (c->cfg.direction == MOST_CH_RX)
  		num_buffer = arm_mbo_chain(c, c->cfg.direction,
  					   most_read_completion);
  	else
  		num_buffer = arm_mbo_chain(c, c->cfg.direction,
  					   most_write_completion);
  	if (unlikely(!num_buffer)) {
  		ret = -ENOMEM;
  		goto err_put_module;
  	}
  
  	ret = run_enqueue_thread(c, id);
  	if (ret)
  		goto err_put_module;
  
  	c->is_starving = 0;
  	c->pipe0.num_buffers = c->cfg.num_buffers / 2;
  	c->pipe1.num_buffers = c->cfg.num_buffers - c->pipe0.num_buffers;
  	atomic_set(&c->mbo_ref, num_buffer);
  
  out:
  	if (comp == c->pipe0.comp)
  		c->pipe0.refs++;
  	if (comp == c->pipe1.comp)
  		c->pipe1.refs++;
  	mutex_unlock(&c->start_mutex);
  	return 0;
  
  err_put_module:
  	module_put(iface->mod);
  	mutex_unlock(&c->start_mutex);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(most_start_channel);
  
  /**
   * most_stop_channel - stops a running channel
   * @iface: pointer to interface instance
   * @id: channel ID
   * @comp: driver component
   */
  int most_stop_channel(struct most_interface *iface, int id,
  		      struct most_component *comp)
  {
  	struct most_channel *c;
  
  	if (unlikely((!iface) || (id >= iface->num_channels) || (id < 0))) {
  		pr_err("Bad interface or index out of range\n");
  		return -EINVAL;
  	}
  	c = iface->p->channel[id];
  	if (unlikely(!c))
  		return -EINVAL;
  
  	mutex_lock(&c->start_mutex);
  	if (c->pipe0.refs + c->pipe1.refs >= 2)
  		goto out;
  
  	if (c->hdm_enqueue_task)
  		kthread_stop(c->hdm_enqueue_task);
  	c->hdm_enqueue_task = NULL;
  
  	if (iface->mod)
  		module_put(iface->mod);
  
  	c->is_poisoned = true;
  	if (c->iface->poison_channel(c->iface, c->channel_id)) {
  		dev_err(&c->dev, "Failed to stop channel %d of interface %s\n", c->channel_id,
  			c->iface->description);
  		mutex_unlock(&c->start_mutex);
  		return -EAGAIN;
  	}
  	flush_trash_fifo(c);
  	flush_channel_fifos(c);
  
  #ifdef CMPL_INTERRUPTIBLE
  	if (wait_for_completion_interruptible(&c->cleanup)) {
  		dev_err(&c->dev, "Interrupted while cleaning up channel %d\n", c->channel_id);
  		mutex_unlock(&c->start_mutex);
  		return -EINTR;
  	}
  #else
  	wait_for_completion(&c->cleanup);
  #endif
  	c->is_poisoned = false;
  
  out:
  	if (comp == c->pipe0.comp)
  		c->pipe0.refs--;
  	if (comp == c->pipe1.comp)
  		c->pipe1.refs--;
  	mutex_unlock(&c->start_mutex);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(most_stop_channel);
  
  /**
   * most_register_component - registers a driver component with the core
   * @comp: driver component
   */
  int most_register_component(struct most_component *comp)
  {
  	if (!comp) {
  		pr_err("Bad component\n");
  		return -EINVAL;
  	}
  	list_add_tail(&comp->list, &comp_list);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(most_register_component);
  
  static int disconnect_channels(struct device *dev, void *data)
  {
  	struct most_interface *iface;
  	struct most_channel *c, *tmp;
  	struct most_component *comp = data;
  
  	iface = dev_get_drvdata(dev);
  	list_for_each_entry_safe(c, tmp, &iface->p->channel_list, list) {
  		if (c->pipe0.comp == comp || c->pipe1.comp == comp)
  			comp->disconnect_channel(c->iface, c->channel_id);
  		if (c->pipe0.comp == comp)
  			c->pipe0.comp = NULL;
  		if (c->pipe1.comp == comp)
  			c->pipe1.comp = NULL;
  	}
  	return 0;
  }
  
  /**
   * most_deregister_component - deregisters a driver component with the core
   * @comp: driver component
   */
  int most_deregister_component(struct most_component *comp)
  {
  	if (!comp) {
  		pr_err("Bad component\n");
  		return -EINVAL;
  	}
  
  	bus_for_each_dev(&mostbus, NULL, comp, disconnect_channels);
  	list_del(&comp->list);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(most_deregister_component);
  
  static void release_channel(struct device *dev)
  {
  	struct most_channel *c = to_channel(dev);
  
  	kfree(c);
  }
  
  /**
   * most_register_interface - registers an interface with core
   * @iface: device interface
   *
   * Allocates and initializes a new interface instance and all of its channels.
   * Returns a pointer to kobject or an error pointer.
   */
  int most_register_interface(struct most_interface *iface)
  {
  	unsigned int i;
  	int id;
  	struct most_channel *c;
  
  	if (!iface || !iface->enqueue || !iface->configure ||
  	    !iface->poison_channel || (iface->num_channels > MAX_CHANNELS))
  		return -EINVAL;
  
  	id = ida_simple_get(&mdev_id, 0, 0, GFP_KERNEL);
  	if (id < 0) {
  		dev_err(iface->dev, "Failed to allocate device ID\n");
  		return id;
  	}
  
  	iface->p = kzalloc(sizeof(*iface->p), GFP_KERNEL);
  	if (!iface->p) {
  		ida_simple_remove(&mdev_id, id);
  		return -ENOMEM;
  	}
  
  	INIT_LIST_HEAD(&iface->p->channel_list);
  	iface->p->dev_id = id;
  	strscpy(iface->p->name, iface->description, sizeof(iface->p->name));
  	iface->dev->bus = &mostbus;
  	iface->dev->groups = interface_attr_groups;
  	dev_set_drvdata(iface->dev, iface);
  	if (device_register(iface->dev)) {
  		dev_err(iface->dev, "Failed to register interface device\n");
  		kfree(iface->p);
  		put_device(iface->dev);
  		ida_simple_remove(&mdev_id, id);
  		return -ENOMEM;
  	}
  
  	for (i = 0; i < iface->num_channels; i++) {
  		const char *name_suffix = iface->channel_vector[i].name_suffix;
  
  		c = kzalloc(sizeof(*c), GFP_KERNEL);
  		if (!c)
  			goto err_free_resources;
  		if (!name_suffix)
  			snprintf(c->name, STRING_SIZE, "ch%d", i);
  		else
  			snprintf(c->name, STRING_SIZE, "%s", name_suffix);
  		c->dev.init_name = c->name;
  		c->dev.parent = iface->dev;
  		c->dev.groups = channel_attr_groups;
  		c->dev.release = release_channel;
  		iface->p->channel[i] = c;
  		c->is_starving = 0;
  		c->iface = iface;
  		c->channel_id = i;
  		c->keep_mbo = false;
  		c->enqueue_halt = false;
  		c->is_poisoned = false;
  		c->cfg.direction = 0;
  		c->cfg.data_type = 0;
  		c->cfg.num_buffers = 0;
  		c->cfg.buffer_size = 0;
  		c->cfg.subbuffer_size = 0;
  		c->cfg.packets_per_xact = 0;
  		spin_lock_init(&c->fifo_lock);
  		INIT_LIST_HEAD(&c->fifo);
  		INIT_LIST_HEAD(&c->trash_fifo);
  		INIT_LIST_HEAD(&c->halt_fifo);
  		init_completion(&c->cleanup);
  		atomic_set(&c->mbo_ref, 0);
  		mutex_init(&c->start_mutex);
  		mutex_init(&c->nq_mutex);
  		list_add_tail(&c->list, &iface->p->channel_list);
  		if (device_register(&c->dev)) {
  			dev_err(&c->dev, "Failed to register channel device\n");
  			goto err_free_most_channel;
  		}
  	}
  	most_interface_register_notify(iface->description);
  	return 0;
  
  err_free_most_channel:
  	put_device(&c->dev);
  
  err_free_resources:
  	while (i > 0) {
  		c = iface->p->channel[--i];
  		device_unregister(&c->dev);
  	}
  	kfree(iface->p);
  	device_unregister(iface->dev);
  	ida_simple_remove(&mdev_id, id);
  	return -ENOMEM;
  }
  EXPORT_SYMBOL_GPL(most_register_interface);
  
  /**
   * most_deregister_interface - deregisters an interface with core
   * @iface: device interface
   *
   * Before removing an interface instance from the list, all running
   * channels are stopped and poisoned.
   */
  void most_deregister_interface(struct most_interface *iface)
  {
  	int i;
  	struct most_channel *c;
  
  	for (i = 0; i < iface->num_channels; i++) {
  		c = iface->p->channel[i];
  		if (c->pipe0.comp)
  			c->pipe0.comp->disconnect_channel(c->iface,
  							c->channel_id);
  		if (c->pipe1.comp)
  			c->pipe1.comp->disconnect_channel(c->iface,
  							c->channel_id);
  		c->pipe0.comp = NULL;
  		c->pipe1.comp = NULL;
  		list_del(&c->list);
  		device_unregister(&c->dev);
  	}
  
  	ida_simple_remove(&mdev_id, iface->p->dev_id);
  	kfree(iface->p);
  	device_unregister(iface->dev);
  }
  EXPORT_SYMBOL_GPL(most_deregister_interface);
  
  /**
   * most_stop_enqueue - prevents core from enqueueing MBOs
   * @iface: pointer to interface
   * @id: channel id
   *
   * This is called by an HDM that _cannot_ attend to its duties and
   * is imminent to get run over by the core. The core is not going to
   * enqueue any further packets unless the flagging HDM calls
   * most_resume enqueue().
   */
  void most_stop_enqueue(struct most_interface *iface, int id)
  {
  	struct most_channel *c = iface->p->channel[id];
  
  	if (!c)
  		return;
  
  	mutex_lock(&c->nq_mutex);
  	c->enqueue_halt = true;
  	mutex_unlock(&c->nq_mutex);
  }
  EXPORT_SYMBOL_GPL(most_stop_enqueue);
  
  /**
   * most_resume_enqueue - allow core to enqueue MBOs again
   * @iface: pointer to interface
   * @id: channel id
   *
   * This clears the enqueue halt flag and enqueues all MBOs currently
   * sitting in the wait fifo.
   */
  void most_resume_enqueue(struct most_interface *iface, int id)
  {
  	struct most_channel *c = iface->p->channel[id];
  
  	if (!c)
  		return;
  
  	mutex_lock(&c->nq_mutex);
  	c->enqueue_halt = false;
  	mutex_unlock(&c->nq_mutex);
  
  	wake_up_interruptible(&c->hdm_fifo_wq);
  }
  EXPORT_SYMBOL_GPL(most_resume_enqueue);
  
  static int __init most_init(void)
  {
  	int err;
  
  	INIT_LIST_HEAD(&comp_list);
  	ida_init(&mdev_id);
  
  	err = bus_register(&mostbus);
  	if (err) {
  		pr_err("Failed to register most bus\n");
  		return err;
  	}
  	err = driver_register(&mostbus_driver);
  	if (err) {
  		pr_err("Failed to register core driver\n");
  		goto err_unregister_bus;
  	}
  	configfs_init();
  	return 0;
  
  err_unregister_bus:
  	bus_unregister(&mostbus);
  	return err;
  }
  
  static void __exit most_exit(void)
  {
  	driver_unregister(&mostbus_driver);
  	bus_unregister(&mostbus);
  	ida_destroy(&mdev_id);
  }
  
  subsys_initcall(most_init);
  module_exit(most_exit);
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Christian Gromm <christian.gromm@microchip.com>");
  MODULE_DESCRIPTION("Core module of stacked MOST Linux driver");
  