/*
   * Intel(R) Trace Hub Memory Storage Unit
   *
   * Copyright (C) 2014-2015 Intel 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.
   */
  
  #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
  
  #include <linux/types.h>
  #include <linux/module.h>
  #include <linux/device.h>
  #include <linux/uaccess.h>
  #include <linux/sizes.h>
  #include <linux/printk.h>
  #include <linux/slab.h>
  #include <linux/mm.h>
  #include <linux/fs.h>
  #include <linux/io.h>
  #include <linux/dma-mapping.h>
  
  #include <asm/cacheflush.h>
  
  #include "intel_th.h"
  #include "msu.h"
  
  #define msc_dev(x) (&(x)->thdev->dev)
  
  /**
   * struct msc_block - multiblock mode block descriptor
   * @bdesc:	pointer to hardware descriptor (beginning of the block)
   * @addr:	physical address of the block
   */
  struct msc_block {
  	struct msc_block_desc	*bdesc;
  	dma_addr_t		addr;
  };
  
  /**
   * struct msc_window - multiblock mode window descriptor
   * @entry:	window list linkage (msc::win_list)
   * @pgoff:	page offset into the buffer that this window starts at
   * @nr_blocks:	number of blocks (pages) in this window
   * @block:	array of block descriptors
   */
  struct msc_window {
  	struct list_head	entry;
  	unsigned long		pgoff;
  	unsigned int		nr_blocks;
  	struct msc		*msc;
  	struct msc_block	block[0];
  };
  
  /**
   * struct msc_iter - iterator for msc buffer
   * @entry:		msc::iter_list linkage
   * @msc:		pointer to the MSC device
   * @start_win:		oldest window
   * @win:		current window
   * @offset:		current logical offset into the buffer
   * @start_block:	oldest block in the window
   * @block:		block number in the window
   * @block_off:		offset into current block
   * @wrap_count:		block wrapping handling
   * @eof:		end of buffer reached
   */
  struct msc_iter {
  	struct list_head	entry;
  	struct msc		*msc;
  	struct msc_window	*start_win;
  	struct msc_window	*win;
  	unsigned long		offset;
  	int			start_block;
  	int			block;
  	unsigned int		block_off;
  	unsigned int		wrap_count;
  	unsigned int		eof;
  };
  
  /**
   * struct msc - MSC device representation
   * @reg_base:		register window base address
   * @thdev:		intel_th_device pointer
   * @win_list:		list of windows in multiblock mode
   * @nr_pages:		total number of pages allocated for this buffer
   * @single_sz:		amount of data in single mode
   * @single_wrap:	single mode wrap occurred
   * @base:		buffer's base pointer
   * @base_addr:		buffer's base address
   * @user_count:		number of users of the buffer
   * @mmap_count:		number of mappings
   * @buf_mutex:		mutex to serialize access to buffer-related bits
  
   * @enabled:		MSC is enabled
   * @wrap:		wrapping is enabled
   * @mode:		MSC operating mode
   * @burst_len:		write burst length
   * @index:		number of this MSC in the MSU
   */
  struct msc {
  	void __iomem		*reg_base;
  	struct intel_th_device	*thdev;
  
  	struct list_head	win_list;
  	unsigned long		nr_pages;
  	unsigned long		single_sz;
  	unsigned int		single_wrap : 1;
  	void			*base;
  	dma_addr_t		base_addr;
  
  	/* <0: no buffer, 0: no users, >0: active users */
  	atomic_t		user_count;
  
  	atomic_t		mmap_count;
  	struct mutex		buf_mutex;
  
  	struct mutex		iter_mutex;
  	struct list_head	iter_list;
  
  	/* config */
  	unsigned int		enabled : 1,
  				wrap	: 1;
  	unsigned int		mode;
  	unsigned int		burst_len;
  	unsigned int		index;
  };
  
  static inline bool msc_block_is_empty(struct msc_block_desc *bdesc)
  {
  	/* header hasn't been written */
  	if (!bdesc->valid_dw)
  		return true;
  
  	/* valid_dw includes the header */
  	if (!msc_data_sz(bdesc))
  		return true;
  
  	return false;
  }
  
  /**
   * msc_oldest_window() - locate the window with oldest data
   * @msc:	MSC device
   *
   * This should only be used in multiblock mode. Caller should hold the
   * msc::user_count reference.
   *
   * Return:	the oldest window with valid data
   */
  static struct msc_window *msc_oldest_window(struct msc *msc)
  {
  	struct msc_window *win;
  	u32 reg = ioread32(msc->reg_base + REG_MSU_MSC0NWSA);
  	unsigned long win_addr = (unsigned long)reg << PAGE_SHIFT;
  	unsigned int found = 0;
  
  	if (list_empty(&msc->win_list))
  		return NULL;
  
  	/*
  	 * we might need a radix tree for this, depending on how
  	 * many windows a typical user would allocate; ideally it's
  	 * something like 2, in which case we're good
  	 */
  	list_for_each_entry(win, &msc->win_list, entry) {
  		if (win->block[0].addr == win_addr)
  			found++;
  
  		/* skip the empty ones */
  		if (msc_block_is_empty(win->block[0].bdesc))
  			continue;
  
  		if (found)
  			return win;
  	}
  
  	return list_entry(msc->win_list.next, struct msc_window, entry);
  }
  
  /**
   * msc_win_oldest_block() - locate the oldest block in a given window
   * @win:	window to look at
   *
   * Return:	index of the block with the oldest data
   */
  static unsigned int msc_win_oldest_block(struct msc_window *win)
  {
  	unsigned int blk;
  	struct msc_block_desc *bdesc = win->block[0].bdesc;
  
  	/* without wrapping, first block is the oldest */
  	if (!msc_block_wrapped(bdesc))
  		return 0;
  
  	/*
  	 * with wrapping, last written block contains both the newest and the
  	 * oldest data for this window.
  	 */
  	for (blk = 0; blk < win->nr_blocks; blk++) {
  		bdesc = win->block[blk].bdesc;
  
  		if (msc_block_last_written(bdesc))
  			return blk;
  	}
  
  	return 0;
  }
  
  /**
   * msc_is_last_win() - check if a window is the last one for a given MSC
   * @win:	window
   * Return:	true if @win is the last window in MSC's multiblock buffer
   */
  static inline bool msc_is_last_win(struct msc_window *win)
  {
  	return win->entry.next == &win->msc->win_list;
  }
  
  /**
   * msc_next_window() - return next window in the multiblock buffer
   * @win:	current window
   *
   * Return:	window following the current one
   */
  static struct msc_window *msc_next_window(struct msc_window *win)
  {
  	if (msc_is_last_win(win))
  		return list_entry(win->msc->win_list.next, struct msc_window,
  				  entry);
  
  	return list_entry(win->entry.next, struct msc_window, entry);
  }
  
  static struct msc_block_desc *msc_iter_bdesc(struct msc_iter *iter)
  {
  	return iter->win->block[iter->block].bdesc;
  }
  
  static void msc_iter_init(struct msc_iter *iter)
  {
  	memset(iter, 0, sizeof(*iter));
  	iter->start_block = -1;
  	iter->block = -1;
  }
  
  static struct msc_iter *msc_iter_install(struct msc *msc)
  {
  	struct msc_iter *iter;
  
  	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
  	if (!iter)
  		return NULL;
  
  	msc_iter_init(iter);
  	iter->msc = msc;
  
  	mutex_lock(&msc->iter_mutex);
  	list_add_tail(&iter->entry, &msc->iter_list);
  	mutex_unlock(&msc->iter_mutex);
  
  	return iter;
  }
  
  static void msc_iter_remove(struct msc_iter *iter, struct msc *msc)
  {
  	mutex_lock(&msc->iter_mutex);
  	list_del(&iter->entry);
  	mutex_unlock(&msc->iter_mutex);
  
  	kfree(iter);
  }
  
  static void msc_iter_block_start(struct msc_iter *iter)
  {
  	if (iter->start_block != -1)
  		return;
  
  	iter->start_block = msc_win_oldest_block(iter->win);
  	iter->block = iter->start_block;
  	iter->wrap_count = 0;
  
  	/*
  	 * start with the block with oldest data; if data has wrapped
  	 * in this window, it should be in this block
  	 */
  	if (msc_block_wrapped(msc_iter_bdesc(iter)))
  		iter->wrap_count = 2;
  
  }
  
  static int msc_iter_win_start(struct msc_iter *iter, struct msc *msc)
  {
  	/* already started, nothing to do */
  	if (iter->start_win)
  		return 0;
  
  	iter->start_win = msc_oldest_window(msc);
  	if (!iter->start_win)
  		return -EINVAL;
  
  	iter->win = iter->start_win;
  	iter->start_block = -1;
  
  	msc_iter_block_start(iter);
  
  	return 0;
  }
  
  static int msc_iter_win_advance(struct msc_iter *iter)
  {
  	iter->win = msc_next_window(iter->win);
  	iter->start_block = -1;
  
  	if (iter->win == iter->start_win) {
  		iter->eof++;
  		return 1;
  	}
  
  	msc_iter_block_start(iter);
  
  	return 0;
  }
  
  static int msc_iter_block_advance(struct msc_iter *iter)
  {
  	iter->block_off = 0;
  
  	/* wrapping */
  	if (iter->wrap_count && iter->block == iter->start_block) {
  		iter->wrap_count--;
  		if (!iter->wrap_count)
  			/* copied newest data from the wrapped block */
  			return msc_iter_win_advance(iter);
  	}
  
  	/* no wrapping, check for last written block */
  	if (!iter->wrap_count && msc_block_last_written(msc_iter_bdesc(iter)))
  		/* copied newest data for the window */
  		return msc_iter_win_advance(iter);
  
  	/* block advance */
  	if (++iter->block == iter->win->nr_blocks)
  		iter->block = 0;
  
  	/* no wrapping, sanity check in case there is no last written block */
  	if (!iter->wrap_count && iter->block == iter->start_block)
  		return msc_iter_win_advance(iter);
  
  	return 0;
  }
  
  /**
   * msc_buffer_iterate() - go through multiblock buffer's data
   * @iter:	iterator structure
   * @size:	amount of data to scan
   * @data:	callback's private data
   * @fn:		iterator callback
   *
   * This will start at the window which will be written to next (containing
   * the oldest data) and work its way to the current window, calling @fn
   * for each chunk of data as it goes.
   *
   * Caller should have msc::user_count reference to make sure the buffer
   * doesn't disappear from under us.
   *
   * Return:	amount of data actually scanned.
   */
  static ssize_t
  msc_buffer_iterate(struct msc_iter *iter, size_t size, void *data,
  		   unsigned long (*fn)(void *, void *, size_t))
  {
  	struct msc *msc = iter->msc;
  	size_t len = size;
  	unsigned int advance;
  
  	if (iter->eof)
  		return 0;
  
  	/* start with the oldest window */
  	if (msc_iter_win_start(iter, msc))
  		return 0;
  
  	do {
  		unsigned long data_bytes = msc_data_sz(msc_iter_bdesc(iter));
  		void *src = (void *)msc_iter_bdesc(iter) + MSC_BDESC;
  		size_t tocopy = data_bytes, copied = 0;
  		size_t remaining = 0;
  
  		advance = 1;
  
  		/*
  		 * If block wrapping happened, we need to visit the last block
  		 * twice, because it contains both the oldest and the newest
  		 * data in this window.
  		 *
  		 * First time (wrap_count==2), in the very beginning, to collect
  		 * the oldest data, which is in the range
  		 * (data_bytes..DATA_IN_PAGE).
  		 *
  		 * Second time (wrap_count==1), it's just like any other block,
  		 * containing data in the range of [MSC_BDESC..data_bytes].
  		 */
  		if (iter->block == iter->start_block && iter->wrap_count) {
  			tocopy = DATA_IN_PAGE - data_bytes;
  			src += data_bytes;
  		}
  
  		if (!tocopy)
  			goto next_block;
  
  		tocopy -= iter->block_off;
  		src += iter->block_off;
  
  		if (len < tocopy) {
  			tocopy = len;
  			advance = 0;
  		}
  
  		remaining = fn(data, src, tocopy);
  
  		if (remaining)
  			advance = 0;
  
  		copied = tocopy - remaining;
  		len -= copied;
  		iter->block_off += copied;
  		iter->offset += copied;
  
  		if (!advance)
  			break;
  
  next_block:
  		if (msc_iter_block_advance(iter))
  			break;
  
  	} while (len);
  
  	return size - len;
  }
  
  /**
   * msc_buffer_clear_hw_header() - clear hw header for multiblock
   * @msc:	MSC device
   */
  static void msc_buffer_clear_hw_header(struct msc *msc)
  {
  	struct msc_window *win;
  
  	mutex_lock(&msc->buf_mutex);
  	list_for_each_entry(win, &msc->win_list, entry) {
  		unsigned int blk;
  		size_t hw_sz = sizeof(struct msc_block_desc) -
  			offsetof(struct msc_block_desc, hw_tag);
  
  		for (blk = 0; blk < win->nr_blocks; blk++) {
  			struct msc_block_desc *bdesc = win->block[blk].bdesc;
  
  			memset(&bdesc->hw_tag, 0, hw_sz);
  		}
  	}
  	mutex_unlock(&msc->buf_mutex);
  }
  
  /**
   * msc_configure() - set up MSC hardware
   * @msc:	the MSC device to configure
   *
   * Program storage mode, wrapping, burst length and trace buffer address
   * into a given MSC. If msc::enabled is set, enable the trace, too.
   */
  static int msc_configure(struct msc *msc)
  {
  	u32 reg;
  
  	if (msc->mode > MSC_MODE_MULTI)
  		return -ENOTSUPP;
  
  	if (msc->mode == MSC_MODE_MULTI)
  		msc_buffer_clear_hw_header(msc);
  
  	reg = msc->base_addr >> PAGE_SHIFT;
  	iowrite32(reg, msc->reg_base + REG_MSU_MSC0BAR);
  
  	if (msc->mode == MSC_MODE_SINGLE) {
  		reg = msc->nr_pages;
  		iowrite32(reg, msc->reg_base + REG_MSU_MSC0SIZE);
  	}
  
  	reg = ioread32(msc->reg_base + REG_MSU_MSC0CTL);
  	reg &= ~(MSC_MODE | MSC_WRAPEN | MSC_EN | MSC_RD_HDR_OVRD);
  
  	reg |= msc->mode << __ffs(MSC_MODE);
  	reg |= msc->burst_len << __ffs(MSC_LEN);
  	/*if (msc->mode == MSC_MODE_MULTI)
  	  reg |= MSC_RD_HDR_OVRD; */
  	if (msc->wrap)
  		reg |= MSC_WRAPEN;
  	if (msc->enabled)
  		reg |= MSC_EN;
  
  	iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);
  
  	if (msc->enabled) {
  		msc->thdev->output.multiblock = msc->mode == MSC_MODE_MULTI;
  		intel_th_trace_enable(msc->thdev);
  	}
  
  	return 0;
  }
  
  /**
   * msc_disable() - disable MSC hardware
   * @msc:	MSC device to disable
   *
   * If @msc is enabled, disable tracing on the switch and then disable MSC
   * storage.
   */
  static void msc_disable(struct msc *msc)
  {
  	unsigned long count;
  	u32 reg;
  
  	if (!msc->enabled)
  		return;
  
  	intel_th_trace_disable(msc->thdev);
  
  	for (reg = 0, count = MSC_PLE_WAITLOOP_DEPTH;
  	     count && !(reg & MSCSTS_PLE); count--) {
  		reg = ioread32(msc->reg_base + REG_MSU_MSC0STS);
  		cpu_relax();
  	}
  
  	if (!count)
  		dev_dbg(msc_dev(msc), "timeout waiting for MSC0 PLE
  ");
  
  	if (msc->mode == MSC_MODE_SINGLE) {
  		msc->single_wrap = !!(reg & MSCSTS_WRAPSTAT);
  
  		reg = ioread32(msc->reg_base + REG_MSU_MSC0MWP);
  		msc->single_sz = reg & ((msc->nr_pages << PAGE_SHIFT) - 1);
  		dev_dbg(msc_dev(msc), "MSCnMWP: %08x/%08lx, wrap: %d
  ",
  			reg, msc->single_sz, msc->single_wrap);
  	}
  
  	reg = ioread32(msc->reg_base + REG_MSU_MSC0CTL);
  	reg &= ~MSC_EN;
  	iowrite32(reg, msc->reg_base + REG_MSU_MSC0CTL);
  	msc->enabled = 0;
  
  	iowrite32(0, msc->reg_base + REG_MSU_MSC0BAR);
  	iowrite32(0, msc->reg_base + REG_MSU_MSC0SIZE);
  
  	dev_dbg(msc_dev(msc), "MSCnNWSA: %08x
  ",
  		ioread32(msc->reg_base + REG_MSU_MSC0NWSA));
  
  	reg = ioread32(msc->reg_base + REG_MSU_MSC0STS);
  	dev_dbg(msc_dev(msc), "MSCnSTS: %08x
  ", reg);
  }
  
  static int intel_th_msc_activate(struct intel_th_device *thdev)
  {
  	struct msc *msc = dev_get_drvdata(&thdev->dev);
  	int ret = 0;
  
  	if (!atomic_inc_unless_negative(&msc->user_count))
  		return -ENODEV;
  
  	mutex_lock(&msc->iter_mutex);
  	if (!list_empty(&msc->iter_list))
  		ret = -EBUSY;
  	mutex_unlock(&msc->iter_mutex);
  
  	if (ret) {
  		atomic_dec(&msc->user_count);
  		return ret;
  	}
  
  	msc->enabled = 1;
  
  	return msc_configure(msc);
  }
  
  static void intel_th_msc_deactivate(struct intel_th_device *thdev)
  {
  	struct msc *msc = dev_get_drvdata(&thdev->dev);
  
  	msc_disable(msc);
  
  	atomic_dec(&msc->user_count);
  }
  
  /**
   * msc_buffer_contig_alloc() - allocate a contiguous buffer for SINGLE mode
   * @msc:	MSC device
   * @size:	allocation size in bytes
   *
   * This modifies msc::base, which requires msc::buf_mutex to serialize, so the
   * caller is expected to hold it.
   *
   * Return:	0 on success, -errno otherwise.
   */
  static int msc_buffer_contig_alloc(struct msc *msc, unsigned long size)
  {
  	unsigned int order = get_order(size);
  	struct page *page;
  
  	if (!size)
  		return 0;
  
  	page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
  	if (!page)
  		return -ENOMEM;
  
  	split_page(page, order);
  	msc->nr_pages = size >> PAGE_SHIFT;
  	msc->base = page_address(page);
  	msc->base_addr = page_to_phys(page);
  
  	return 0;
  }
  
  /**
   * msc_buffer_contig_free() - free a contiguous buffer
   * @msc:	MSC configured in SINGLE mode
   */
  static void msc_buffer_contig_free(struct msc *msc)
  {
  	unsigned long off;
  
  	for (off = 0; off < msc->nr_pages << PAGE_SHIFT; off += PAGE_SIZE) {
  		struct page *page = virt_to_page(msc->base + off);
  
  		page->mapping = NULL;
  		__free_page(page);
  	}
  
  	msc->nr_pages = 0;
  }
  
  /**
   * msc_buffer_contig_get_page() - find a page at a given offset
   * @msc:	MSC configured in SINGLE mode
   * @pgoff:	page offset
   *
   * Return:	page, if @pgoff is within the range, NULL otherwise.
   */
  static struct page *msc_buffer_contig_get_page(struct msc *msc,
  					       unsigned long pgoff)
  {
  	if (pgoff >= msc->nr_pages)
  		return NULL;
  
  	return virt_to_page(msc->base + (pgoff << PAGE_SHIFT));
  }
  
  /**
   * msc_buffer_win_alloc() - alloc a window for a multiblock mode
   * @msc:	MSC device
   * @nr_blocks:	number of pages in this window
   *
   * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
   * to serialize, so the caller is expected to hold it.
   *
   * Return:	0 on success, -errno otherwise.
   */
  static int msc_buffer_win_alloc(struct msc *msc, unsigned int nr_blocks)
  {
  	struct msc_window *win;
  	unsigned long size = PAGE_SIZE;
  	int i, ret = -ENOMEM;
  
  	if (!nr_blocks)
  		return 0;
  
  	win = kzalloc(offsetof(struct msc_window, block[nr_blocks]),
  		      GFP_KERNEL);
  	if (!win)
  		return -ENOMEM;
  
  	if (!list_empty(&msc->win_list)) {
  		struct msc_window *prev = list_entry(msc->win_list.prev,
  						     struct msc_window, entry);
  
  		win->pgoff = prev->pgoff + prev->nr_blocks;
  	}
  
  	for (i = 0; i < nr_blocks; i++) {
  		win->block[i].bdesc = dma_alloc_coherent(msc_dev(msc), size,
  							 &win->block[i].addr,
  							 GFP_KERNEL);
  
  #ifdef CONFIG_X86
  		/* Set the page as uncached */
  		set_memory_uc((unsigned long)win->block[i].bdesc, 1);
  #endif
  
  		if (!win->block[i].bdesc)
  			goto err_nomem;
  	}
  
  	win->msc = msc;
  	win->nr_blocks = nr_blocks;
  
  	if (list_empty(&msc->win_list)) {
  		msc->base = win->block[0].bdesc;
  		msc->base_addr = win->block[0].addr;
  	}
  
  	list_add_tail(&win->entry, &msc->win_list);
  	msc->nr_pages += nr_blocks;
  
  	return 0;
  
  err_nomem:
  	for (i--; i >= 0; i--) {
  #ifdef CONFIG_X86
  		/* Reset the page to write-back before releasing */
  		set_memory_wb((unsigned long)win->block[i].bdesc, 1);
  #endif
  		dma_free_coherent(msc_dev(msc), size, win->block[i].bdesc,
  				  win->block[i].addr);
  	}
  	kfree(win);
  
  	return ret;
  }
  
  /**
   * msc_buffer_win_free() - free a window from MSC's window list
   * @msc:	MSC device
   * @win:	window to free
   *
   * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
   * to serialize, so the caller is expected to hold it.
   */
  static void msc_buffer_win_free(struct msc *msc, struct msc_window *win)
  {
  	int i;
  
  	msc->nr_pages -= win->nr_blocks;
  
  	list_del(&win->entry);
  	if (list_empty(&msc->win_list)) {
  		msc->base = NULL;
  		msc->base_addr = 0;
  	}
  
  	for (i = 0; i < win->nr_blocks; i++) {
  		struct page *page = virt_to_page(win->block[i].bdesc);
  
  		page->mapping = NULL;
  #ifdef CONFIG_X86
  		/* Reset the page to write-back before releasing */
  		set_memory_wb((unsigned long)win->block[i].bdesc, 1);
  #endif
  		dma_free_coherent(msc_dev(win->msc), PAGE_SIZE,
  				  win->block[i].bdesc, win->block[i].addr);
  	}
  
  	kfree(win);
  }
  
  /**
   * msc_buffer_relink() - set up block descriptors for multiblock mode
   * @msc:	MSC device
   *
   * This traverses msc::win_list, which requires msc::buf_mutex to serialize,
   * so the caller is expected to hold it.
   */
  static void msc_buffer_relink(struct msc *msc)
  {
  	struct msc_window *win, *next_win;
  
  	/* call with msc::mutex locked */
  	list_for_each_entry(win, &msc->win_list, entry) {
  		unsigned int blk;
  		u32 sw_tag = 0;
  
  		/*
  		 * Last window's next_win should point to the first window
  		 * and MSC_SW_TAG_LASTWIN should be set.
  		 */
  		if (msc_is_last_win(win)) {
  			sw_tag |= MSC_SW_TAG_LASTWIN;
  			next_win = list_entry(msc->win_list.next,
  					      struct msc_window, entry);
  		} else {
  			next_win = list_entry(win->entry.next,
  					      struct msc_window, entry);
  		}
  
  		for (blk = 0; blk < win->nr_blocks; blk++) {
  			struct msc_block_desc *bdesc = win->block[blk].bdesc;
  
  			memset(bdesc, 0, sizeof(*bdesc));
  
  			bdesc->next_win = next_win->block[0].addr >> PAGE_SHIFT;
  
  			/*
  			 * Similarly to last window, last block should point
  			 * to the first one.
  			 */
  			if (blk == win->nr_blocks - 1) {
  				sw_tag |= MSC_SW_TAG_LASTBLK;
  				bdesc->next_blk =
  					win->block[0].addr >> PAGE_SHIFT;
  			} else {
  				bdesc->next_blk =
  					win->block[blk + 1].addr >> PAGE_SHIFT;
  			}
  
  			bdesc->sw_tag = sw_tag;
  			bdesc->block_sz = PAGE_SIZE / 64;
  		}
  	}
  
  	/*
  	 * Make the above writes globally visible before tracing is
  	 * enabled to make sure hardware sees them coherently.
  	 */
  	wmb();
  }
  
  static void msc_buffer_multi_free(struct msc *msc)
  {
  	struct msc_window *win, *iter;
  
  	list_for_each_entry_safe(win, iter, &msc->win_list, entry)
  		msc_buffer_win_free(msc, win);
  }
  
  static int msc_buffer_multi_alloc(struct msc *msc, unsigned long *nr_pages,
  				  unsigned int nr_wins)
  {
  	int ret, i;
  
  	for (i = 0; i < nr_wins; i++) {
  		ret = msc_buffer_win_alloc(msc, nr_pages[i]);
  		if (ret) {
  			msc_buffer_multi_free(msc);
  			return ret;
  		}
  	}
  
  	msc_buffer_relink(msc);
  
  	return 0;
  }
  
  /**
   * msc_buffer_free() - free buffers for MSC
   * @msc:	MSC device
   *
   * Free MSC's storage buffers.
   *
   * This modifies msc::win_list and msc::base, which requires msc::buf_mutex to
   * serialize, so the caller is expected to hold it.
   */
  static void msc_buffer_free(struct msc *msc)
  {
  	if (msc->mode == MSC_MODE_SINGLE)
  		msc_buffer_contig_free(msc);
  	else if (msc->mode == MSC_MODE_MULTI)
  		msc_buffer_multi_free(msc);
  }
  
  /**
   * msc_buffer_alloc() - allocate a buffer for MSC
   * @msc:	MSC device
   * @size:	allocation size in bytes
   *
   * Allocate a storage buffer for MSC, depending on the msc::mode, it will be
   * either done via msc_buffer_contig_alloc() for SINGLE operation mode or
   * msc_buffer_win_alloc() for multiblock operation. The latter allocates one
   * window per invocation, so in multiblock mode this can be called multiple
   * times for the same MSC to allocate multiple windows.
   *
   * This modifies msc::win_list and msc::base, which requires msc::buf_mutex
   * to serialize, so the caller is expected to hold it.
   *
   * Return:	0 on success, -errno otherwise.
   */
  static int msc_buffer_alloc(struct msc *msc, unsigned long *nr_pages,
  			    unsigned int nr_wins)
  {
  	int ret;
  
  	/* -1: buffer not allocated */
  	if (atomic_read(&msc->user_count) != -1)
  		return -EBUSY;
  
  	if (msc->mode == MSC_MODE_SINGLE) {
  		if (nr_wins != 1)
  			return -EINVAL;
  
  		ret = msc_buffer_contig_alloc(msc, nr_pages[0] << PAGE_SHIFT);
  	} else if (msc->mode == MSC_MODE_MULTI) {
  		ret = msc_buffer_multi_alloc(msc, nr_pages, nr_wins);
  	} else {
  		ret = -ENOTSUPP;
  	}
  
  	if (!ret) {
  		/* allocation should be visible before the counter goes to 0 */
  		smp_mb__before_atomic();
  
  		if (WARN_ON_ONCE(atomic_cmpxchg(&msc->user_count, -1, 0) != -1))
  			return -EINVAL;
  	}
  
  	return ret;
  }
  
  /**
   * msc_buffer_unlocked_free_unless_used() - free a buffer unless it's in use
   * @msc:	MSC device
   *
   * This will free MSC buffer unless it is in use or there is no allocated
   * buffer.
   * Caller needs to hold msc::buf_mutex.
   *
   * Return:	0 on successful deallocation or if there was no buffer to
   *		deallocate, -EBUSY if there are active users.
   */
  static int msc_buffer_unlocked_free_unless_used(struct msc *msc)
  {
  	int count, ret = 0;
  
  	count = atomic_cmpxchg(&msc->user_count, 0, -1);
  
  	/* > 0: buffer is allocated and has users */
  	if (count > 0)
  		ret = -EBUSY;
  	/* 0: buffer is allocated, no users */
  	else if (!count)
  		msc_buffer_free(msc);
  	/* < 0: no buffer, nothing to do */
  
  	return ret;
  }
  
  /**
   * msc_buffer_free_unless_used() - free a buffer unless it's in use
   * @msc:	MSC device
   *
   * This is a locked version of msc_buffer_unlocked_free_unless_used().
   */
  static int msc_buffer_free_unless_used(struct msc *msc)
  {
  	int ret;
  
  	mutex_lock(&msc->buf_mutex);
  	ret = msc_buffer_unlocked_free_unless_used(msc);
  	mutex_unlock(&msc->buf_mutex);
  
  	return ret;
  }
  
  /**
   * msc_buffer_get_page() - get MSC buffer page at a given offset
   * @msc:	MSC device
   * @pgoff:	page offset into the storage buffer
   *
   * This traverses msc::win_list, so holding msc::buf_mutex is expected from
   * the caller.
   *
   * Return:	page if @pgoff corresponds to a valid buffer page or NULL.
   */
  static struct page *msc_buffer_get_page(struct msc *msc, unsigned long pgoff)
  {
  	struct msc_window *win;
  
  	if (msc->mode == MSC_MODE_SINGLE)
  		return msc_buffer_contig_get_page(msc, pgoff);
  
  	list_for_each_entry(win, &msc->win_list, entry)
  		if (pgoff >= win->pgoff && pgoff < win->pgoff + win->nr_blocks)
  			goto found;
  
  	return NULL;
  
  found:
  	pgoff -= win->pgoff;
  	return virt_to_page(win->block[pgoff].bdesc);
  }
  
  /**
   * struct msc_win_to_user_struct - data for copy_to_user() callback
   * @buf:	userspace buffer to copy data to
   * @offset:	running offset
   */
  struct msc_win_to_user_struct {
  	char __user	*buf;
  	unsigned long	offset;
  };
  
  /**
   * msc_win_to_user() - iterator for msc_buffer_iterate() to copy data to user
   * @data:	callback's private data
   * @src:	source buffer
   * @len:	amount of data to copy from the source buffer
   */
  static unsigned long msc_win_to_user(void *data, void *src, size_t len)
  {
  	struct msc_win_to_user_struct *u = data;
  	unsigned long ret;
  
  	ret = copy_to_user(u->buf + u->offset, src, len);
  	u->offset += len - ret;
  
  	return ret;
  }
  
  
  /*
   * file operations' callbacks
   */
  
  static int intel_th_msc_open(struct inode *inode, struct file *file)
  {
  	struct intel_th_device *thdev = file->private_data;
  	struct msc *msc = dev_get_drvdata(&thdev->dev);
  	struct msc_iter *iter;
  
  	if (!capable(CAP_SYS_RAWIO))
  		return -EPERM;
  
  	iter = msc_iter_install(msc);
  	if (!iter)
  		return -ENOMEM;
  
  	file->private_data = iter;
  
  	return nonseekable_open(inode, file);
  }
  
  static int intel_th_msc_release(struct inode *inode, struct file *file)
  {
  	struct msc_iter *iter = file->private_data;
  	struct msc *msc = iter->msc;
  
  	msc_iter_remove(iter, msc);
  
  	return 0;
  }
  
  static ssize_t
  msc_single_to_user(struct msc *msc, char __user *buf, loff_t off, size_t len)
  {
  	unsigned long size = msc->nr_pages << PAGE_SHIFT, rem = len;
  	unsigned long start = off, tocopy = 0;
  
  	if (msc->single_wrap) {
  		start += msc->single_sz;
  		if (start < size) {
  			tocopy = min(rem, size - start);
  			if (copy_to_user(buf, msc->base + start, tocopy))
  				return -EFAULT;
  
  			buf += tocopy;
  			rem -= tocopy;
  			start += tocopy;
  		}
  
  		start &= size - 1;
  		if (rem) {
  			tocopy = min(rem, msc->single_sz - start);
  			if (copy_to_user(buf, msc->base + start, tocopy))
  				return -EFAULT;
  
  			rem -= tocopy;
  		}
  
  		return len - rem;
  	}
  
  	if (copy_to_user(buf, msc->base + start, rem))
  		return -EFAULT;
  
  	return len;
  }
  
  static ssize_t intel_th_msc_read(struct file *file, char __user *buf,
  				 size_t len, loff_t *ppos)
  {
  	struct msc_iter *iter = file->private_data;
  	struct msc *msc = iter->msc;
  	size_t size;
  	loff_t off = *ppos;
  	ssize_t ret = 0;
  
  	if (!atomic_inc_unless_negative(&msc->user_count))
  		return 0;
  
  	if (msc->enabled) {
  		ret = -EBUSY;
  		goto put_count;
  	}
  
  	if (msc->mode == MSC_MODE_SINGLE && !msc->single_wrap)
  		size = msc->single_sz;
  	else
  		size = msc->nr_pages << PAGE_SHIFT;
  
  	if (!size)
  		return 0;
  
  	if (off >= size) {
  		len = 0;
  		goto put_count;
  	}
  	if (off + len >= size)
  		len = size - off;
  
  	if (msc->mode == MSC_MODE_SINGLE) {
  		ret = msc_single_to_user(msc, buf, off, len);
  		if (ret >= 0)
  			*ppos += ret;
  	} else if (msc->mode == MSC_MODE_MULTI) {
  		struct msc_win_to_user_struct u = {
  			.buf	= buf,
  			.offset	= 0,
  		};
  
  		ret = msc_buffer_iterate(iter, len, &u, msc_win_to_user);
  		if (ret >= 0)
  			*ppos = iter->offset;
  	} else {
  		ret = -ENOTSUPP;
  	}
  
  put_count:
  	atomic_dec(&msc->user_count);
  
  	return ret;
  }
  
  /*
   * vm operations callbacks (vm_ops)
   */
  
  static void msc_mmap_open(struct vm_area_struct *vma)
  {
  	struct msc_iter *iter = vma->vm_file->private_data;
  	struct msc *msc = iter->msc;
  
  	atomic_inc(&msc->mmap_count);
  }
  
  static void msc_mmap_close(struct vm_area_struct *vma)
  {
  	struct msc_iter *iter = vma->vm_file->private_data;
  	struct msc *msc = iter->msc;
  	unsigned long pg;
  
  	if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex))
  		return;
  
  	/* drop page _counts */
  	for (pg = 0; pg < msc->nr_pages; pg++) {
  		struct page *page = msc_buffer_get_page(msc, pg);
  
  		if (WARN_ON_ONCE(!page))
  			continue;
  
  		if (page->mapping)
  			page->mapping = NULL;
  	}
  
  	/* last mapping -- drop user_count */
  	atomic_dec(&msc->user_count);
  	mutex_unlock(&msc->buf_mutex);
  }
  
  static int msc_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  {
  	struct msc_iter *iter = vma->vm_file->private_data;
  	struct msc *msc = iter->msc;
  
  	vmf->page = msc_buffer_get_page(msc, vmf->pgoff);
  	if (!vmf->page)
  		return VM_FAULT_SIGBUS;
  
  	get_page(vmf->page);
  	vmf->page->mapping = vma->vm_file->f_mapping;
  	vmf->page->index = vmf->pgoff;
  
  	return 0;
  }
  
  static const struct vm_operations_struct msc_mmap_ops = {
  	.open	= msc_mmap_open,
  	.close	= msc_mmap_close,
  	.fault	= msc_mmap_fault,
  };
  
  static int intel_th_msc_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	unsigned long size = vma->vm_end - vma->vm_start;
  	struct msc_iter *iter = vma->vm_file->private_data;
  	struct msc *msc = iter->msc;
  	int ret = -EINVAL;
  
  	if (!size || offset_in_page(size))
  		return -EINVAL;
  
  	if (vma->vm_pgoff)
  		return -EINVAL;
  
  	/* grab user_count once per mmap; drop in msc_mmap_close() */
  	if (!atomic_inc_unless_negative(&msc->user_count))
  		return -EINVAL;
  
  	if (msc->mode != MSC_MODE_SINGLE &&
  	    msc->mode != MSC_MODE_MULTI)
  		goto out;
  
  	if (size >> PAGE_SHIFT != msc->nr_pages)
  		goto out;
  
  	atomic_set(&msc->mmap_count, 1);
  	ret = 0;
  
  out:
  	if (ret)
  		atomic_dec(&msc->user_count);
  
  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
  	vma->vm_flags |= VM_DONTEXPAND | VM_DONTCOPY;
  	vma->vm_ops = &msc_mmap_ops;
  	return ret;
  }
  
  static const struct file_operations intel_th_msc_fops = {
  	.open		= intel_th_msc_open,
  	.release	= intel_th_msc_release,
  	.read		= intel_th_msc_read,
  	.mmap		= intel_th_msc_mmap,
  	.llseek		= no_llseek,
  };
  
  static int intel_th_msc_init(struct msc *msc)
  {
  	atomic_set(&msc->user_count, -1);
  
  	msc->mode = MSC_MODE_MULTI;
  	mutex_init(&msc->buf_mutex);
  	INIT_LIST_HEAD(&msc->win_list);
  
  	mutex_init(&msc->iter_mutex);
  	INIT_LIST_HEAD(&msc->iter_list);
  
  	msc->burst_len =
  		(ioread32(msc->reg_base + REG_MSU_MSC0CTL) & MSC_LEN) >>
  		__ffs(MSC_LEN);
  
  	return 0;
  }
  
  static const char * const msc_mode[] = {
  	[MSC_MODE_SINGLE]	= "single",
  	[MSC_MODE_MULTI]	= "multi",
  	[MSC_MODE_EXI]		= "ExI",
  	[MSC_MODE_DEBUG]	= "debug",
  };
  
  static ssize_t
  wrap_show(struct device *dev, struct device_attribute *attr, char *buf)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  
  	return scnprintf(buf, PAGE_SIZE, "%d
  ", msc->wrap);
  }
  
  static ssize_t
  wrap_store(struct device *dev, struct device_attribute *attr, const char *buf,
  	   size_t size)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  	unsigned long val;
  	int ret;
  
  	ret = kstrtoul(buf, 10, &val);
  	if (ret)
  		return ret;
  
  	msc->wrap = !!val;
  
  	return size;
  }
  
  static DEVICE_ATTR_RW(wrap);
  
  static ssize_t
  mode_show(struct device *dev, struct device_attribute *attr, char *buf)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  
  	return scnprintf(buf, PAGE_SIZE, "%s
  ", msc_mode[msc->mode]);
  }
  
  static ssize_t
  mode_store(struct device *dev, struct device_attribute *attr, const char *buf,
  	   size_t size)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  	size_t len = size;
  	char *cp;
  	int i, ret;
  
  	if (!capable(CAP_SYS_RAWIO))
  		return -EPERM;
  
  	cp = memchr(buf, '
  ', len);
  	if (cp)
  		len = cp - buf;
  
  	for (i = 0; i < ARRAY_SIZE(msc_mode); i++)
  		if (!strncmp(msc_mode[i], buf, len))
  			goto found;
  
  	return -EINVAL;
  
  found:
  	mutex_lock(&msc->buf_mutex);
  	ret = msc_buffer_unlocked_free_unless_used(msc);
  	if (!ret)
  		msc->mode = i;
  	mutex_unlock(&msc->buf_mutex);
  
  	return ret ? ret : size;
  }
  
  static DEVICE_ATTR_RW(mode);
  
  static ssize_t
  nr_pages_show(struct device *dev, struct device_attribute *attr, char *buf)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  	struct msc_window *win;
  	size_t count = 0;
  
  	mutex_lock(&msc->buf_mutex);
  
  	if (msc->mode == MSC_MODE_SINGLE)
  		count = scnprintf(buf, PAGE_SIZE, "%ld
  ", msc->nr_pages);
  	else if (msc->mode == MSC_MODE_MULTI) {
  		list_for_each_entry(win, &msc->win_list, entry) {
  			count += scnprintf(buf + count, PAGE_SIZE - count,
  					   "%d%c", win->nr_blocks,
  					   msc_is_last_win(win) ? '
  ' : ',');
  		}
  	} else {
  		count = scnprintf(buf, PAGE_SIZE, "unsupported
  ");
  	}
  
  	mutex_unlock(&msc->buf_mutex);
  
  	return count;
  }
  
  static ssize_t
  nr_pages_store(struct device *dev, struct device_attribute *attr,
  	       const char *buf, size_t size)
  {
  	struct msc *msc = dev_get_drvdata(dev);
  	unsigned long val, *win = NULL, *rewin;
  	size_t len = size;
  	const char *p = buf;
  	char *end, *s;
  	int ret, nr_wins = 0;
  
  	if (!capable(CAP_SYS_RAWIO))
  		return -EPERM;
  
  	ret = msc_buffer_free_unless_used(msc);
  	if (ret)
  		return ret;
  
  	/* scan the comma-separated list of allocation sizes */
  	end = memchr(buf, '
  ', len);
  	if (end)
  		len = end - buf;
  
  	do {
  		end = memchr(p, ',', len);
  		s = kstrndup(p, end ? end - p : len, GFP_KERNEL);
  		ret = kstrtoul(s, 10, &val);
  		kfree(s);
  
  		if (ret || !val)
  			goto free_win;
  
  		if (nr_wins && msc->mode == MSC_MODE_SINGLE) {
  			ret = -EINVAL;
  			goto free_win;
  		}
  
  		nr_wins++;
  		rewin = krealloc(win, sizeof(*win) * nr_wins, GFP_KERNEL);
  		if (!rewin) {
  			kfree(win);
  			return -ENOMEM;
  		}
  
  		win = rewin;
  		win[nr_wins - 1] = val;
  
  		if (!end)
  			break;
  
  		len -= end - p;
  		p = end + 1;
  	} while (len);
  
  	mutex_lock(&msc->buf_mutex);
  	ret = msc_buffer_alloc(msc, win, nr_wins);
  	mutex_unlock(&msc->buf_mutex);
  
  free_win:
  	kfree(win);
  
  	return ret ? ret : size;
  }
  
  static DEVICE_ATTR_RW(nr_pages);
  
  static struct attribute *msc_output_attrs[] = {
  	&dev_attr_wrap.attr,
  	&dev_attr_mode.attr,
  	&dev_attr_nr_pages.attr,
  	NULL,
  };
  
  static struct attribute_group msc_output_group = {
  	.attrs	= msc_output_attrs,
  };
  
  static int intel_th_msc_probe(struct intel_th_device *thdev)
  {
  	struct device *dev = &thdev->dev;
  	struct resource *res;
  	struct msc *msc;
  	void __iomem *base;
  	int err;
  
  	res = intel_th_device_get_resource(thdev, IORESOURCE_MEM, 0);
  	if (!res)
  		return -ENODEV;
  
  	base = devm_ioremap(dev, res->start, resource_size(res));
  	if (!base)
  		return -ENOMEM;
  
  	msc = devm_kzalloc(dev, sizeof(*msc), GFP_KERNEL);
  	if (!msc)
  		return -ENOMEM;
  
  	msc->index = thdev->id;
  
  	msc->thdev = thdev;
  	msc->reg_base = base + msc->index * 0x100;
  
  	err = intel_th_msc_init(msc);
  	if (err)
  		return err;
  
  	err = sysfs_create_group(&dev->kobj, &msc_output_group);
  	if (err)
  		return err;
  
  	dev_set_drvdata(dev, msc);
  
  	return 0;
  }
  
  static void intel_th_msc_remove(struct intel_th_device *thdev)
  {
  	sysfs_remove_group(&thdev->dev.kobj, &msc_output_group);
  }
  
  static struct intel_th_driver intel_th_msc_driver = {
  	.probe	= intel_th_msc_probe,
  	.remove	= intel_th_msc_remove,
  	.activate	= intel_th_msc_activate,
  	.deactivate	= intel_th_msc_deactivate,
  	.fops	= &intel_th_msc_fops,
  	.driver	= {
  		.name	= "msc",
  		.owner	= THIS_MODULE,
  	},
  };
  
  module_driver(intel_th_msc_driver,
  	      intel_th_driver_register,
  	      intel_th_driver_unregister);
  
  MODULE_LICENSE("GPL v2");
  MODULE_DESCRIPTION("Intel(R) Trace Hub Memory Storage Unit driver");
  MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");