/*
   * Function Control Protocol (IEC 61883-1) helper functions
   *
   * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
   * Licensed under the terms of the GNU General Public License, version 2.
   */
  
  #include <linux/device.h>
  #include <linux/firewire.h>
  #include <linux/firewire-constants.h>
  #include <linux/list.h>
  #include <linux/module.h>
  #include <linux/sched.h>
  #include <linux/spinlock.h>
  #include <linux/wait.h>
  #include <linux/delay.h>
  #include "fcp.h"
  #include "lib.h"
  
  #define CTS_AVC 0x00
  
  #define ERROR_RETRIES	3
  #define ERROR_DELAY_MS	5
  #define FCP_TIMEOUT_MS	125
  
  static DEFINE_SPINLOCK(transactions_lock);
  static LIST_HEAD(transactions);
  
  enum fcp_state {
  	STATE_PENDING,
  	STATE_BUS_RESET,
  	STATE_COMPLETE,
  };
  
  struct fcp_transaction {
  	struct list_head list;
  	struct fw_unit *unit;
  	void *response_buffer;
  	unsigned int response_size;
  	unsigned int response_match_bytes;
  	enum fcp_state state;
  	wait_queue_head_t wait;
  };
  
  /**
   * fcp_avc_transaction - send an AV/C command and wait for its response
   * @unit: a unit on the target device
   * @command: a buffer containing the command frame; must be DMA-able
   * @command_size: the size of @command
   * @response: a buffer for the response frame
   * @response_size: the maximum size of @response
   * @response_match_bytes: a bitmap specifying the bytes used to detect the
   *                        correct response frame
   *
   * This function sends a FCP command frame to the target and waits for the
   * corresponding response frame to be returned.
   *
   * Because it is possible for multiple FCP transactions to be active at the
   * same time, the correct response frame is detected by the value of certain
   * bytes.  These bytes must be set in @response before calling this function,
   * and the corresponding bits must be set in @response_match_bytes.
   *
   * @command and @response can point to the same buffer.
   *
   * Asynchronous operation (INTERIM, NOTIFY) is not supported at the moment.
   *
   * Returns the actual size of the response frame, or a negative error code.
   */
  int fcp_avc_transaction(struct fw_unit *unit,
  			const void *command, unsigned int command_size,
  			void *response, unsigned int response_size,
  			unsigned int response_match_bytes)
  {
  	struct fcp_transaction t;
  	int tcode, ret, tries = 0;
  
  	t.unit = unit;
  	t.response_buffer = response;
  	t.response_size = response_size;
  	t.response_match_bytes = response_match_bytes;
  	t.state = STATE_PENDING;
  	init_waitqueue_head(&t.wait);
  
  	spin_lock_irq(&transactions_lock);
  	list_add_tail(&t.list, &transactions);
  	spin_unlock_irq(&transactions_lock);
  
  	for (;;) {
  		tcode = command_size == 4 ? TCODE_WRITE_QUADLET_REQUEST
  					  : TCODE_WRITE_BLOCK_REQUEST;
  		ret = snd_fw_transaction(t.unit, tcode,
  					 CSR_REGISTER_BASE + CSR_FCP_COMMAND,
  					 (void *)command, command_size, 0);
  		if (ret < 0)
  			break;
  
  		wait_event_timeout(t.wait, t.state != STATE_PENDING,
  				   msecs_to_jiffies(FCP_TIMEOUT_MS));
  
  		if (t.state == STATE_COMPLETE) {
  			ret = t.response_size;
  			break;
  		} else if (t.state == STATE_BUS_RESET) {
  			msleep(ERROR_DELAY_MS);
  		} else if (++tries >= ERROR_RETRIES) {
  			dev_err(&t.unit->device, "FCP command timed out
  ");
  			ret = -EIO;
  			break;
  		}
  	}
  
  	spin_lock_irq(&transactions_lock);
  	list_del(&t.list);
  	spin_unlock_irq(&transactions_lock);
  
  	return ret;
  }
  EXPORT_SYMBOL(fcp_avc_transaction);
  
  /**
   * fcp_bus_reset - inform the target handler about a bus reset
   * @unit: the unit that might be used by fcp_avc_transaction()
   *
   * This function must be called from the driver's .update handler to inform
   * the FCP transaction handler that a bus reset has happened.  Any pending FCP
   * transactions are retried.
   */
  void fcp_bus_reset(struct fw_unit *unit)
  {
  	struct fcp_transaction *t;
  
  	spin_lock_irq(&transactions_lock);
  	list_for_each_entry(t, &transactions, list) {
  		if (t->unit == unit &&
  		    t->state == STATE_PENDING) {
  			t->state = STATE_BUS_RESET;
  			wake_up(&t->wait);
  		}
  	}
  	spin_unlock_irq(&transactions_lock);
  }
  EXPORT_SYMBOL(fcp_bus_reset);
  
  /* checks whether the response matches the masked bytes in response_buffer */
  static bool is_matching_response(struct fcp_transaction *transaction,
  				 const void *response, size_t length)
  {
  	const u8 *p1, *p2;
  	unsigned int mask, i;
  
  	p1 = response;
  	p2 = transaction->response_buffer;
  	mask = transaction->response_match_bytes;
  
  	for (i = 0; ; ++i) {
  		if ((mask & 1) && p1[i] != p2[i])
  			return false;
  		mask >>= 1;
  		if (!mask)
  			return true;
  		if (--length == 0)
  			return false;
  	}
  }
  
  static void fcp_response(struct fw_card *card, struct fw_request *request,
  			 int tcode, int destination, int source,
  			 int generation, unsigned long long offset,
  			 void *data, size_t length, void *callback_data)
  {
  	struct fcp_transaction *t;
  	unsigned long flags;
  
  	if (length < 1 || (*(const u8 *)data & 0xf0) != CTS_AVC)
  		return;
  
  	spin_lock_irqsave(&transactions_lock, flags);
  	list_for_each_entry(t, &transactions, list) {
  		struct fw_device *device = fw_parent_device(t->unit);
  		if (device->card != card ||
  		    device->generation != generation)
  			continue;
  		smp_rmb(); /* node_id vs. generation */
  		if (device->node_id != source)
  			continue;
  
  		if (t->state == STATE_PENDING &&
  		    is_matching_response(t, data, length)) {
  			t->state = STATE_COMPLETE;
  			t->response_size = min((unsigned int)length,
  					       t->response_size);
  			memcpy(t->response_buffer, data, t->response_size);
  			wake_up(&t->wait);
  		}
  	}
  	spin_unlock_irqrestore(&transactions_lock, flags);
  }
  
  static struct fw_address_handler response_register_handler = {
  	.length = 0x200,
  	.address_callback = fcp_response,
  };
  
  static int __init fcp_module_init(void)
  {
  	static const struct fw_address_region response_register_region = {
  		.start = CSR_REGISTER_BASE + CSR_FCP_RESPONSE,
  		.end = CSR_REGISTER_BASE + CSR_FCP_END,
  	};
  
  	fw_core_add_address_handler(&response_register_handler,
  				    &response_register_region);
  
  	return 0;
  }
  
  static void __exit fcp_module_exit(void)
  {
  	WARN_ON(!list_empty(&transactions));
  	fw_core_remove_address_handler(&response_register_handler);
  }
  
  module_init(fcp_module_init);
  module_exit(fcp_module_exit);