/*
   *
   * Copyright (c) 2009, Microsoft Corporation.
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms and conditions of the GNU General Public License,
   * version 2, as published by the Free Software Foundation.
   *
   * This program is distributed in the hope it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   * more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
   * Place - Suite 330, Boston, MA 02111-1307 USA.
   *
   * Authors:
   *   Haiyang Zhang <haiyangz@microsoft.com>
   *   Hank Janssen  <hjanssen@microsoft.com>
   *   K. Y. Srinivasan <kys@microsoft.com>
   *
   */
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/hyperv.h>
  
  #include "hyperv_vmbus.h"
  
  void hv_begin_read(struct hv_ring_buffer_info *rbi)
  {
  	rbi->ring_buffer->interrupt_mask = 1;
  	mb();
  }
  
  u32 hv_end_read(struct hv_ring_buffer_info *rbi)
  {
  	u32 read;
  	u32 write;
  
  	rbi->ring_buffer->interrupt_mask = 0;
  	mb();
  
  	/*
  	 * Now check to see if the ring buffer is still empty.
  	 * If it is not, we raced and we need to process new
  	 * incoming messages.
  	 */
  	hv_get_ringbuffer_availbytes(rbi, &read, &write);
  
  	return read;
  }
  
  /*
   * When we write to the ring buffer, check if the host needs to
   * be signaled. Here is the details of this protocol:
   *
   *	1. The host guarantees that while it is draining the
   *	   ring buffer, it will set the interrupt_mask to
   *	   indicate it does not need to be interrupted when
   *	   new data is placed.
   *
   *	2. The host guarantees that it will completely drain
   *	   the ring buffer before exiting the read loop. Further,
   *	   once the ring buffer is empty, it will clear the
   *	   interrupt_mask and re-check to see if new data has
   *	   arrived.
   */
  
  static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
  {
  	mb();
  	if (rbi->ring_buffer->interrupt_mask)
  		return false;
  
  	/* check interrupt_mask before read_index */
  	rmb();
  	/*
  	 * This is the only case we need to signal when the
  	 * ring transitions from being empty to non-empty.
  	 */
  	if (old_write == rbi->ring_buffer->read_index)
  		return true;
  
  	return false;
  }
  
  /*
   * To optimize the flow management on the send-side,
   * when the sender is blocked because of lack of
   * sufficient space in the ring buffer, potential the
   * consumer of the ring buffer can signal the producer.
   * This is controlled by the following parameters:
   *
   * 1. pending_send_sz: This is the size in bytes that the
   *    producer is trying to send.
   * 2. The feature bit feat_pending_send_sz set to indicate if
   *    the consumer of the ring will signal when the ring
   *    state transitions from being full to a state where
   *    there is room for the producer to send the pending packet.
   */
  
  static bool hv_need_to_signal_on_read(u32 old_rd,
  					 struct hv_ring_buffer_info *rbi)
  {
  	u32 prev_write_sz;
  	u32 cur_write_sz;
  	u32 r_size;
  	u32 write_loc = rbi->ring_buffer->write_index;
  	u32 read_loc = rbi->ring_buffer->read_index;
  	u32 pending_sz = rbi->ring_buffer->pending_send_sz;
  
  	/*
  	 * If the other end is not blocked on write don't bother.
  	 */
  	if (pending_sz == 0)
  		return false;
  
  	r_size = rbi->ring_datasize;
  	cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
  			read_loc - write_loc;
  
  	prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
  			old_rd - write_loc;
  
  
  	if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
  		return true;
  
  	return false;
  }
  
  /*
   * hv_get_next_write_location()
   *
   * Get the next write location for the specified ring buffer
   *
   */
  static inline u32
  hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
  {
  	u32 next = ring_info->ring_buffer->write_index;
  
  	return next;
  }
  
  /*
   * hv_set_next_write_location()
   *
   * Set the next write location for the specified ring buffer
   *
   */
  static inline void
  hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
  		     u32 next_write_location)
  {
  	ring_info->ring_buffer->write_index = next_write_location;
  }
  
  /*
   * hv_get_next_read_location()
   *
   * Get the next read location for the specified ring buffer
   */
  static inline u32
  hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
  {
  	u32 next = ring_info->ring_buffer->read_index;
  
  	return next;
  }
  
  /*
   * hv_get_next_readlocation_withoffset()
   *
   * Get the next read location + offset for the specified ring buffer.
   * This allows the caller to skip
   */
  static inline u32
  hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
  				 u32 offset)
  {
  	u32 next = ring_info->ring_buffer->read_index;
  
  	next += offset;
  	next %= ring_info->ring_datasize;
  
  	return next;
  }
  
  /*
   *
   * hv_set_next_read_location()
   *
   * Set the next read location for the specified ring buffer
   *
   */
  static inline void
  hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
  		    u32 next_read_location)
  {
  	ring_info->ring_buffer->read_index = next_read_location;
  }
  
  
  /*
   *
   * hv_get_ring_buffer()
   *
   * Get the start of the ring buffer
   */
  static inline void *
  hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
  {
  	return (void *)ring_info->ring_buffer->buffer;
  }
  
  
  /*
   *
   * hv_get_ring_buffersize()
   *
   * Get the size of the ring buffer
   */
  static inline u32
  hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
  {
  	return ring_info->ring_datasize;
  }
  
  /*
   *
   * hv_get_ring_bufferindices()
   *
   * Get the read and write indices as u64 of the specified ring buffer
   *
   */
  static inline u64
  hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
  {
  	return (u64)ring_info->ring_buffer->write_index << 32;
  }
  
  /*
   *
   * hv_copyfrom_ringbuffer()
   *
   * Helper routine to copy to source from ring buffer.
   * Assume there is enough room. Handles wrap-around in src case only!!
   *
   */
  static u32 hv_copyfrom_ringbuffer(
  	struct hv_ring_buffer_info	*ring_info,
  	void				*dest,
  	u32				destlen,
  	u32				start_read_offset)
  {
  	void *ring_buffer = hv_get_ring_buffer(ring_info);
  	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
  
  	u32 frag_len;
  
  	/* wrap-around detected at the src */
  	if (destlen > ring_buffer_size - start_read_offset) {
  		frag_len = ring_buffer_size - start_read_offset;
  
  		memcpy(dest, ring_buffer + start_read_offset, frag_len);
  		memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
  	} else
  
  		memcpy(dest, ring_buffer + start_read_offset, destlen);
  
  
  	start_read_offset += destlen;
  	start_read_offset %= ring_buffer_size;
  
  	return start_read_offset;
  }
  
  
  /*
   *
   * hv_copyto_ringbuffer()
   *
   * Helper routine to copy from source to ring buffer.
   * Assume there is enough room. Handles wrap-around in dest case only!!
   *
   */
  static u32 hv_copyto_ringbuffer(
  	struct hv_ring_buffer_info	*ring_info,
  	u32				start_write_offset,
  	void				*src,
  	u32				srclen)
  {
  	void *ring_buffer = hv_get_ring_buffer(ring_info);
  	u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
  	u32 frag_len;
  
  	/* wrap-around detected! */
  	if (srclen > ring_buffer_size - start_write_offset) {
  		frag_len = ring_buffer_size - start_write_offset;
  		memcpy(ring_buffer + start_write_offset, src, frag_len);
  		memcpy(ring_buffer, src + frag_len, srclen - frag_len);
  	} else
  		memcpy(ring_buffer + start_write_offset, src, srclen);
  
  	start_write_offset += srclen;
  	start_write_offset %= ring_buffer_size;
  
  	return start_write_offset;
  }
  
  /*
   *
   * hv_ringbuffer_get_debuginfo()
   *
   * Get various debug metrics for the specified ring buffer
   *
   */
  void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
  			    struct hv_ring_buffer_debug_info *debug_info)
  {
  	u32 bytes_avail_towrite;
  	u32 bytes_avail_toread;
  
  	if (ring_info->ring_buffer) {
  		hv_get_ringbuffer_availbytes(ring_info,
  					&bytes_avail_toread,
  					&bytes_avail_towrite);
  
  		debug_info->bytes_avail_toread = bytes_avail_toread;
  		debug_info->bytes_avail_towrite = bytes_avail_towrite;
  		debug_info->current_read_index =
  			ring_info->ring_buffer->read_index;
  		debug_info->current_write_index =
  			ring_info->ring_buffer->write_index;
  		debug_info->current_interrupt_mask =
  			ring_info->ring_buffer->interrupt_mask;
  	}
  }
  
  /*
   *
   * hv_ringbuffer_init()
   *
   *Initialize the ring buffer
   *
   */
  int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
  		   void *buffer, u32 buflen)
  {
  	if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
  		return -EINVAL;
  
  	memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
  
  	ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
  	ring_info->ring_buffer->read_index =
  		ring_info->ring_buffer->write_index = 0;
  
  	ring_info->ring_size = buflen;
  	ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
  
  	spin_lock_init(&ring_info->ring_lock);
  
  	return 0;
  }
  
  /*
   *
   * hv_ringbuffer_cleanup()
   *
   * Cleanup the ring buffer
   *
   */
  void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
  {
  }
  
  /*
   *
   * hv_ringbuffer_write()
   *
   * Write to the ring buffer
   *
   */
  int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
  		    struct scatterlist *sglist, u32 sgcount, bool *signal)
  {
  	int i = 0;
  	u32 bytes_avail_towrite;
  	u32 bytes_avail_toread;
  	u32 totalbytes_towrite = 0;
  
  	struct scatterlist *sg;
  	u32 next_write_location;
  	u32 old_write;
  	u64 prev_indices = 0;
  	unsigned long flags;
  
  	for_each_sg(sglist, sg, sgcount, i)
  	{
  		totalbytes_towrite += sg->length;
  	}
  
  	totalbytes_towrite += sizeof(u64);
  
  	spin_lock_irqsave(&outring_info->ring_lock, flags);
  
  	hv_get_ringbuffer_availbytes(outring_info,
  				&bytes_avail_toread,
  				&bytes_avail_towrite);
  
  
  	/* If there is only room for the packet, assume it is full. */
  	/* Otherwise, the next time around, we think the ring buffer */
  	/* is empty since the read index == write index */
  	if (bytes_avail_towrite <= totalbytes_towrite) {
  		spin_unlock_irqrestore(&outring_info->ring_lock, flags);
  		return -EAGAIN;
  	}
  
  	/* Write to the ring buffer */
  	next_write_location = hv_get_next_write_location(outring_info);
  
  	old_write = next_write_location;
  
  	for_each_sg(sglist, sg, sgcount, i)
  	{
  		next_write_location = hv_copyto_ringbuffer(outring_info,
  						     next_write_location,
  						     sg_virt(sg),
  						     sg->length);
  	}
  
  	/* Set previous packet start */
  	prev_indices = hv_get_ring_bufferindices(outring_info);
  
  	next_write_location = hv_copyto_ringbuffer(outring_info,
  					     next_write_location,
  					     &prev_indices,
  					     sizeof(u64));
  
  	/* Issue a full memory barrier before updating the write index */
  	mb();
  
  	/* Now, update the write location */
  	hv_set_next_write_location(outring_info, next_write_location);
  
  
  	spin_unlock_irqrestore(&outring_info->ring_lock, flags);
  
  	*signal = hv_need_to_signal(old_write, outring_info);
  	return 0;
  }
  
  
  /*
   *
   * hv_ringbuffer_peek()
   *
   * Read without advancing the read index
   *
   */
  int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
  		   void *Buffer, u32 buflen)
  {
  	u32 bytes_avail_towrite;
  	u32 bytes_avail_toread;
  	u32 next_read_location = 0;
  	unsigned long flags;
  
  	spin_lock_irqsave(&Inring_info->ring_lock, flags);
  
  	hv_get_ringbuffer_availbytes(Inring_info,
  				&bytes_avail_toread,
  				&bytes_avail_towrite);
  
  	/* Make sure there is something to read */
  	if (bytes_avail_toread < buflen) {
  
  		spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
  
  		return -EAGAIN;
  	}
  
  	/* Convert to byte offset */
  	next_read_location = hv_get_next_read_location(Inring_info);
  
  	next_read_location = hv_copyfrom_ringbuffer(Inring_info,
  						Buffer,
  						buflen,
  						next_read_location);
  
  	spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
  
  	return 0;
  }
  
  
  /*
   *
   * hv_ringbuffer_read()
   *
   * Read and advance the read index
   *
   */
  int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
  		   u32 buflen, u32 offset, bool *signal)
  {
  	u32 bytes_avail_towrite;
  	u32 bytes_avail_toread;
  	u32 next_read_location = 0;
  	u64 prev_indices = 0;
  	unsigned long flags;
  	u32 old_read;
  
  	if (buflen <= 0)
  		return -EINVAL;
  
  	spin_lock_irqsave(&inring_info->ring_lock, flags);
  
  	hv_get_ringbuffer_availbytes(inring_info,
  				&bytes_avail_toread,
  				&bytes_avail_towrite);
  
  	old_read = bytes_avail_toread;
  
  	/* Make sure there is something to read */
  	if (bytes_avail_toread < buflen) {
  		spin_unlock_irqrestore(&inring_info->ring_lock, flags);
  
  		return -EAGAIN;
  	}
  
  	next_read_location =
  		hv_get_next_readlocation_withoffset(inring_info, offset);
  
  	next_read_location = hv_copyfrom_ringbuffer(inring_info,
  						buffer,
  						buflen,
  						next_read_location);
  
  	next_read_location = hv_copyfrom_ringbuffer(inring_info,
  						&prev_indices,
  						sizeof(u64),
  						next_read_location);
  
  	/* Make sure all reads are done before we update the read index since */
  	/* the writer may start writing to the read area once the read index */
  	/*is updated */
  	mb();
  
  	/* Update the read index */
  	hv_set_next_read_location(inring_info, next_read_location);
  
  	spin_unlock_irqrestore(&inring_info->ring_lock, flags);
  
  	*signal = hv_need_to_signal_on_read(old_read, inring_info);
  
  	return 0;
  }